Peter C. Ellsworth, Virginia Barkley, Tim Dennehy, Ben DeGain, Bob Ellingson, Steve Naranjo 1 , Maria Sims
University of Arizona, Arizona Pest Management Center & 1 USDA-ARS-ALARC
Abstract
When a product performs better or worse than expectations, there are many biological, ecological, and operational factors that must be examined. Genetic resistance to the pesticide itself is often a concern. The control interval depends on the ecological impact of biotic (e.g., presence and function of natural enemies) and abiotic (e.g., frequency and severity of storms) factors. Timing, rates, and application methods used are also key factors affecting product performance.
A four-year study to evaluate pyriproxyfen (Knack ® ) field performance in Arizona was initiated in 2004, after levels of whitefly susceptibility in statewide surveys were observed to be decreasing. Grower sites in Maricopa, Buckeye, Wellton, and Marana were used. We controlled for major operational factors by using a common timing, rate, and aerial application for each Knack spray. Resistance bio-assays were conducted on progeny of field-collected adults, pre- and postspray. New eggs were marked in-field prior to spraying and examined in the field and lab in order to isolate Knack-associated mortality caused by direct toxicity as well as by ecological factors (e.g., bioresidual). Nymphal bioassays were used to evaluate metamorphosis inhibition. Population trends were estimated using standard sampling methods. Appropriate check plots were compared to the Knack treatment.
Study results suggest Knack field performance and pyriproxyfen resistance has not changed significantly among the years or locations examined to date. In 2005, many struggled to gain control over whitefly populations. This work indicated that
Knack performance and resistance parameters were within the range expected for the last several years. However, operational and ecological barriers to the performance of Knack and other chemistry were in play. Late planted conditions, lush winter vegetation capable of hosting whiteflies, poor growing conditions, and an extended period of extreme immigration pressure were all factors that diminished the impact of Knack and other products in 2005. In contrast, the winter preceding 2006 was among the driest on record followed by a very active monsoon season in central Arizona. High winds and dust movement, and a very active natural enemy community helped to continually lower whitefly populations. The result was a whitefly season characterized as light, with overall foliar insecticide usage setting a 28-yr record low for Arizona cotton. Barring all other operational and ecological factors at work, control intervals should have been similar each year. Yet, observed intervals have been different (e.g., 2005 vs. 2006) and point to the importance of these external factors in assessing product performance.
Work will continue in 2007 to identify factors that contribute to whitefly outbreak conditions. These data will be key to understanding any performance changes, either due to operational or ecological factors mentioned above or due to innate
Arizona Cotton Report (P-151) July 2007 167

changes in whitefly susceptibility. This will be important in advising growers about the risk factors associated with whitefly outbreaks and should lead to recommendations for minimizing these risks.
Introduction
After laboratory bioassays showed disturbing trends towards decreased levels of whitefly ( Bemisia tabaci ) susceptibility to pyriproxyfen in certain locales in Arizona in 2003, we initiated a comprehensive assessment of pyriproxyfen field performance against whitefly in cotton in 2004 with major support for these pilot studies from Arizona Cotton Growers
Association (ACGA) and initial seed-support from Valent USA, and continued in 2005-2006 with a grant from AZ
Cotton Research and Protection Council (ACRPC) provided by Valent USA. Knack Insect Growth Regulator ® has been a key to the stabilization of whitefly management in Arizona since 1996 and to the continued prevention of any
“stickiness” episodes over the last decade (Ellsworth & Martinez-Carrillo 2001).
Our field performance assessment includes a detailed monitoring of multiple field sites distributed throughout Arizona and representing the relative risks of pyriproxyfen resistance identified in laboratory bioassays. Each site included, at a minimum, significant acreages that were treated with Knack in contrast to acreages left untreated. We used the following procedures: 1) detailed monitoring of whitefly population dynamics; 2) monitoring of the associated natural enemy complex; 3) pre- and post-spray resistance monitoring of whiteflies to pyriproxyfen (by Dennehy et al.); and 4) in-field evaluations of the bio- and chemical residual of pyriproxyfen. These latter methods will be key to understanding any performance losses that might be associated with lower susceptibilities identified through conventional resistance monitoring, which currently uses laboratory bioassays to determine whitefly susceptibilities to Knack concentrations of 0.1 ug / ml.
For this study, currently the third year of a four-year study, Knack performance was compared across sites to determine any geographical differences in whitefly control. This study should 1) help assess and quantify the reliability of Knack for whitefly control, 2) identify any performance-eroding changes in susceptibility, providing valuable insight into the conditions where product failures might become likely, and 3) allow us to advise growers about potential options in whitefly management. Armed with this information and new understanding of these relationships, we hope to be able to better advise growers about the consequences of lowered susceptibilities in their area and to recommend best management practices for avoiding altogether or managing resistance present in whitefly populations.
Materials & Methods
Generalized Approaches to Field Design and Maintenance (2004–2006)
Each field site consisted of a large (≥ ca. 0.7 A; > 4 A at commercial sites) block of cotton to which Knack was applied aerially when B. tabaci populations exceeded established IGR thresholds of 3-5 adults per 5th main-stem leaf with 1 large nymph per quarter-sized disk (or 40%:40% on the binomial system; Diehl et al. 1996; Ellsworth et al.
1995, 1996a,b, 2006). In 2006, populations were exceptionally low, and a spray was initiated prior to threshold being reached [1.3 adults per leaf (12%) with 0.4 large nymphs per disk (28%)]. At each site, an adjacent block of similar area was left as an untreated control. Where possible, fields were selected where no previous sprays had been made which targeted or otherwise impacted whitefly populations, where no sprays were made against whiteflies in either plot until the whitefly threshold had been re-reached, and where sprays against other pests were not necessary for at least 8 days after the initial Knack application. In 2006 Wellton site, the pest control advisor elected to spray a broadspectrum insecticide ca. 2 weeks after the initiation of the study (endosulfan @ 1.5 lbs ai / A). This did not impact the bioassays, because they had already been removed from the field. Bt cotton is preferred and has been used in all sites so far with only one exception (2006 Wellton).
Three commercial sites were used for the 2004-2006 programs, Wellton, Buckeye, and Maricopa. In 2004, an additional site in Marana was used as well. The Maricopa site was located at the Maricopa Agricultural Center Demonstration
Farm. The experimental design for this site was an 18 A site consisting of a randomized complete block with four
Arizona Cotton Report (P-151) July 2007 168

replicates (Fig. 1). The Wellton site included one large commercial area (140 A) subdivided into 16 individual fields
(each ca. 9 A in size). Two fields were treated with Knack (8 oz/A) by air and two were left untreated. Other commercial compounds (Oberon, Intruder, Courier, and Venom) were used by air in some of the other fields. The Buckeye site was one large commercial field (75 A) divided into two replicate halves. The grower had spent ca. 2 weeks planting this field, and the eastern half was decidedly more advanced in plant growth than the western half. Each replicate contained two treatments, Knack by air and an untreated check (UTC). An upper and lower 50 ft buffer was established around the field to eliminate edge effects; this buffer was treated with Intruder (2.3 oz / A) at the same time that the test was initiated. In addition, un-replicated plots were established for other commercial products in the area between the two replicates. Only the Knack and UTC plots are detailed here. Knack was applied by air at 8 oz / A and 5 GPA at all
3 sites by commercial aircraft. Knack was also applied in replicate plots by ground (15 GPA) at the Maricopa site.
Both the Wellton and Buckeye sites were replicated twice; Maricopa four times. As in 2004 and 2005, Dennehy et al. conducted resistance monitoring at all three sites (data not shown), just prior to the first spray and then at least 30 days later. The 2005 sites were also conducted at Maricopa Agricultural Center, Buckeye, and Wellton. The Maricopa experimental design consisted of a randomized complete block with six treatments replicated four times with similar application methods used in 2006. Wellton included one large commercial field split in half, one side treated with
Knack (8 oz/A) by air and the other side left untreated. The Buckeye site was one large commercial field split into four plots, including one each for Knack and the UTC. In 2004, sites in Maricopa, Buckeye, Wellton and Marana were used. The Maricopa Agricultural Center site was approximately 18 A comprised of 6 large ground sprayed blocks and
3 aerial sprayed blocks. The Buckeye experimental design was identical to the one in 2005. The 2004 Wellton was close to the site used in the subsequent year and was split into four 10 A plots. The Marana site in 2004 consisted of
19
N
2006 Whitefly Efficacy Evaluations
Airstrip
Field 25 Benches 4 and 3
Ditch a b
120x120, 0.3A
10
9 b a rotation split B b a
11 a b
12 c a d b
14 d b
78 rows c a
13 b a
15 a b
16
30 ft turn-around b a a b
26 a b
25
27 a b
28 b a
30 a b
29 c a
31 c
32 b
20 ft d b a d
120 ft
2 b a a b
1
32 rows a b
6 b a
5
36 rows
7 b a a b
18 a b
19 b a
21 c a
20
6 row skips b d b d
22 c a
40 ft alleys c d
3
120x260, 0.72 A a b d c
4 a b b a
8 a b
17 a b
23 a b
24
680 ft
N
I
U
K
O
C
1. Knack -G
0.054 lbs ai / A
15 GPA
2. Knack -A
0.054 lbs ai / A
5 GPA
3. Oberon -G
0.188 lbs ai / A
15 GPA
4. Oberon -A
0.125 lbs ai / A
5 GPA
5. Courier
0.35 lbs ai / A
15 GPA
6. NNI0101
0.045 lbs ai / A
15 GPA
7. Intruder
0.10 lbs / A
15 GPA
8. UTC
Test
Planted 4/13/06 - 4/14/06 with
DP 449BR and irrigated on
4/17/06 - 4/18/06.
Plot Design
Four replicates of eight treatments.
Ground sprayed plots 36 rows x 120 ft.
Aerial sprayed plots 78 rows x 120 ft.
Split rotation of 4 treatments within aerial plots.
Total of 24 ground and 8 aerial plots.
6 row skips between plots with 40 ft. alleys.
Figure 1.
Plot map for the 2006 whitefly evaluations in Maricopa, AZ.
12/17/06 pce
Figure 1. 2006 plot plan, Maricopa, AZ (06F25wf).
As in 2004, the field bioassays consisted of three basic approaches (more detailed methods provided in the next section); however, a modification was made in 2005 and continued in 2006 to address logistical efficiencies . In 2004, we followed these procedures: a) egg bioassays established prior to the Knack application and left in the field for a period of ca. 7 days, b) egg bioassays established immediately after Knack was applied in the field on excised leaves brought to the lab, and c) nymphal bioassays established on a companion set of leaves also brought into the lab. In
Arizona Cotton Report (P-151) July 2007 169

2005 and 2006, (b) was modified such that all eggs were identified in the field just prior to application (along with the eggs used in (a). They were then retrieved from the field immediately after the application (within 24 hrs) and held in the lab as in the 2004 assays. The nymph bioassays tell us specific information about the impact of pyriproxyfen on whitefly metamorphosis, an area in which we have little historical information. The two egg bioassays parse out the overall field mortality possible (i.e., bioresidual) in Knack regimes versus what is caused by Knack alone (i.e., chemical residual).
Bioassays
In Situ Egg Bioresidual Bioassays—Field Cohort
No more than 24 h prior to Knack application, a minimum of 200 newly-deposited (white) B. tabaci eggs were located on 4th main-stem leaves within each of the two (three at MAC) treatments (Knack, UTC) per site. To avoid edge effects, only rows comprising the central 50% of each plot were used, and no sampling was conducted nearer than 25 m from plot margins. Efforts were made to collect samples spatially representative of this central area. Crews used
15x hand lenses to locate suitable eggs that were circled using a fine-tipped permanent non-toxic pen and specially constructed 8x hand lenses. No more than five eggs were referenced on any single leaf. To facilitate leaf recovery, paper tags were attached to petioles of leaves containing referenced eggs, and survey flagging attached to the internode just below the tagged leaf. Prior to exiting each plot, suitability of referenced eggs were verified with 22x hand lenses by Bob Ellingson (2004), Peter Ellsworth (2004, 2005, & 2006), and Maria Sims (2006), at which time petiole tags were sequentially numbered to facilitate complete recovery of referenced eggs.
At ca. 7 DAT, the remaining marked leaves (see next procedure) were removed, placed individually within ziplock bags, and returned to the laboratory for inspection. Untreated plots were, as a general rule, sampled prior to Knack-treated plots to avoid secondary transfer or contamination. Additionally, separate coolers were used to transport materials harvested from each treatment. Dedicated Knack and Knack-free coolers were designated for these purposes. All laboratory procedures, when applicable, exercised similar precautions (e.g. UTC material handled first with dedicated
Knack-free equipment). Upon arrival to the lab, leaf blades were trimmed to a rectangular shape; petioles were freshly cut and leaf bioassay arenas transferred to individual Aquapiks ® and held at 75–85°F until inspection could be performed under high powered dissecting microscope. Once egg hatch reached its maximum in the UTC, marked eggs were characterized as being either eclosed normally, dislodged (missing), preyed upon (by sucking or chewing predators), or intact but inviable. A minuten was used to facilitate manipulation and examination of egg tissues.
Egg Chemical Residual Bioassays of Direct Effects of Knack—Laboratory Cohort
Another ca. 200 eggs per treatment were set-up along with eggs in the field cohort, but then collected within 24 h following Knack field application (i.e., in contrast to the field cohort that remained in the field for 7 d). These 4th main-stem leaves contained our marked B. tabaci eggs (2005–2006; or were marked after collection in the lab in
2004), as well as a population of 1 st – 4 th instars. Leaves were placed individually within ziplock bags, and returned to the laboratory, where all predators were removed and leaves prepared in Aquapiks as described above. A nymphal cohort was also established on these leaves in the lab (see below). Eggs were inspected and characterized as either eclosed normally, or intact but inviable as described above. Other losses to predators or leaf desiccation in the lab were excluded from the analyses.
Nymphal Cohort Bioassays of Direct Effects of Knack (Metamorphosis Inhibition)
Cohorts of at least ca. 50 nymphs each for instars 1, 2 and 3 as well as a small number of putatively non-susceptible
4 th instars were marked on leaves of each treatment using a non-toxic felt-tip pen. These nymphs were regularly inspected for any change in their mortality status. Final categories included normal adult emergence, dead (inviable), or parasitized. Other losses to predators or leaf desiccation in the lab were excluded from the analyses.
Resistance Monitoring Bioassays
The resistance monitoring procedure is established by EARML protocols and already conducted as part of a larger
Arizona Cotton Report (P-151) July 2007 170

effort to track resistances of whiteflies to various chemistries in Arizona by Dennehy et al. In relation to this study,
EARML personnel were alerted as to when a target field was approaching the IGR-threshold. Usually ca. 24 h prior to the Knack spray, EARML personnel collected a pre-spray adult population from each of the plots identified in the target field. These mass collections gave rise to eggs in the laboratory that were then subjected to standard concentrations of pyriproxyfen for establishing resistance responses. Then, ca. 30 days after the Knack field spray, EARML personnel returned to the target field and made new collections of adults to be handled in the same manner for a post-spray evaluation. Where possible, appropriate replication was followed throughout.
Analyses
Mortality can be calculated and examined in a variety of ways, including apparent and marginal mortality rates,
Abbott’s or Schneider corrected mortality, or by other appropriate means for comparing populations.
For the Maricopa site (2004–2006), where physically replicated plots were available, these plots served as replicates, four in total. At Wellton and Buckeye, rows where different members of the crew were setting up the in situ assays served as the unit of replication (N=3). Apparent rates of egg inviability (unhatched) were calculated excluding individuals lost to predation or dislodgement (missing). Because these losses were so small over the 24 h that the eggs were in the field for the lab cohort, this approximates the sum of apparent inviability due to natural causes (background rates of sterility in untreated eggs) plus the chemical sterilization effects of Knack. Marginal mortality rates were calculated for the relevant factors using standard methods (Naranjo & Ellsworth, 2005).
Calculation of mortalities derived from these types of studies can be methodologically diverse. Further, because of the methodological change in the lab cohort bioassays, there were some small changes in the approach to calculation of mortalities (marginal and/or “corrected” mortalities). In 2005 & 2006, eggs from the lab cohort were left in the field for up to 24 hrs during which eggs were subject to mortality factors theoretically not present in the laboratory (i.e., predation and dislodgement). The rates of losses over this less than 24 h period were quite small; however, they were excluded from certain calculations as a result. In addition, as in 2004, a certain fraction of our cohort was lost in the laboratory either due to predation (i.e., from predators brought in with the samples and not excluded) or to losses in leaf quality. These individuals were excluded from all analyses.
Key to assessing Knack performance is parsing out the chemical effects from the biological residual of the regime in the field. There are a number of ways this can be done. In the cohort that was isolated from the field but held in the laboratory, the chemical effects of Knack on egg viability can, in theory, be directly measured when compared to appropriate controls (UTC). Using the inviability rates identified above, Schneider’s correction for the UTC provides rates of mortality associated with Knack. Abbott’s correction was also used. These two corrections are probably our best approach to parsing out chemical effects in the laboratory cohorts, though the latter is very sensitive to unequal sample sizes as occurs at times in these studies.
For the field cohorts, mortality due directly to the chemical effects of Knack is confounded by all the other mortality factors operating in the field simultaneously. Thus, the analytic approach here is to calculate the rate of egg inviability in the UTC and subtract that value from the rate present in the Knack regimes. This gives rise to an adjusted rate for egg inviability found in Knack regimes in excess of “background” inviability present in the UTC. However, it does not properly estimate the potential rate of egg mortality due to Knack per se because of the other factors present (i.e., missing and predation). Thus, marginal rates for “insecticide” (M insecticide
) can be calculated from apparent rates for
“missing” (A m
) and “predation” (A p
) as well as for the Knack-adjusted rate of inviability (A k-adj
):
M insecticide
= A k-adj
/ [1-(A m
+ A p
)].
Rates for the nymphal cohorts from each location for all years were adjusted using Schneider’s or Abbott’s corrections.
However, survival of nymphs (2006) in Knack-treated regimes were so low—10, 2, and 3 individuals surviving to adulthood in Buckeye, Maricopa, and Wellton, respectively—that the inferences drawn from these values should be guarded. Numbers of survivors for the 2005 nymphal cohorts were also quite low. Similar observations were made for 2004, with one marked exception of 19 survivors from the Marana Knack treated field. A category of “dead adult” further confounds interpretation. At times, we found high rates of practically eclosed adults that failed to properly
Arizona Cotton Report (P-151) July 2007 171

develop and move from the exuviae.
Results
Maricopa
At Maricopa (2006), populations were at historic lows. Because threshold conditions were not expected to occur prior to crop cut-out, we elected to treat with all compounds prior to threshold (< 0.5 large nymphs per disk & < 2 adults per leaf). This was in stark contrast to 2005, when populations grew at unprecedented rates and area-wide pressure was extreme. Historically, a typical pattern of population development is as follows (Fig. 2). Once threshold is reached,
Knack is applied; populations continue to increase for an additional 1–2 weeks (based on large nymphs per disk); populations then collapse; and in general, a protracted interval of sub-threshold suppression follows for an additional
2–6 weeks. This trend was not evident in 2003 when applications were intentionally delayed after the threshold was reached. In 2004, a later planted field was subjected to a hailstorm that broke off the upper portions of many plants and partially defoliated or injured leaves throughout. The resulting plant growth and whitefly distribution was unusual and applications were delayed by as much as 15 d. “Control” was satisfactory in 2003 but not so in 2004, no matter what chemistry was used (Fig. 3). In 2005 (Fig. 3), cotton was once again planted late (i.e., in May) and the resulting
“control” interval and outcomes were not satisfactory no matter what compound was used. Conversely, in 2006, all chemistry was used very early (relative to established thresholds) and populations were maintained well below threshold season-long thereafter including in the UTC (Fig. 4).
3
2
1
0
1996
1997 7
1998
8 9
6 0
6
0
2000 1999
7
2002
6 6
6
9 7
6
0
2 8
0
2 7
2
9
6
8
2
6
9
8
6
9
0
7
2
0
6
7
6
6
2
0
8
2
6
6
9
2
0 8
7
2
6 6
9
0
8
7
2
6
9
6
9
8 7
9
8
2 2
7 2
9
8
6
7
9
8
6
June July August September
Figure 2.
Population dynamics of whitefly large nymphs (3rd and 4th instars per
6
9
8
(1996–2000, 2002), Knack (@ 8 oz / A) was ground-applied to cotton according to Extension guidelines at 1 large nymph per disk (and 3–5 adults per leaf, not shown). Population responses are noticeably
Population responses are noticeably consistent—increases after applications to
29
Arizona Cotton Report (P-151) July 2007 172

5
5
16
14
12
10
8
6
4
2
0
2005
5
2004
4
4
5
6
2
6
6
2
6
9 7
6
0
2
8
6
7
0
8
5
3
2
9
5
8
0
3
4
7
0
4
9
6
4
5
4
4
7
9
8
5
6
0
9
3
6
8
3
9
6
2 0
6
8
4
7
3
2
6
4
3
9
0 8
3
7
2
6
3
0 8 7
2
6 9
3
6 9
8 7
6
3
5
5
9
8
6
9
8
June July August September
Figure 16. In 2003 (red) and 2004 (purple), the Knack application was delayed by 10 and 15 d, respectively. The population trend was different from our historical standards. The 2004 & 2005 planting
3
2.5
2
1.5
1
0.5
0 and indicate timing of Knack application. [2005: replicated large plots; 2003-4: unreplicated, commercial demonstrations; Note change in scale from Fig. 2].
9 8
0
4
7
3
6
6
0
3
2.5
4
7
5
6
5
3 0
6
3
2
3
2
8
6
9
5
6 0
2
7
5
6
6
0
9 7
4
6
6 1.5
5
6
3
6 6
3
8
2
0
2
7
2
9
8
6
7
3
1
2 2
9 7
2
8
9
6
8
9
0
0
2
5 0
0.5
June July
6
5
Figure 17. Enlargement of scale from figure 15 for comparisons of
6
0
7
0 2 2
2 2
9 7
8 7
9
8 7
9
8 population patterns around the time of first application with Knack.
6
8
0
4
9
4
7
5
3
8
4
2
6
9
8
0
7
5
6
9
3
2
0
6
8
3
5
7
6
2
0
9
6
8
4
Figure 4.
Enlargement of scale from Fig. 3 and inclusion of 2006 data (dark green with bullet symbols) for comparisons of population patterns around the time of first application with Knack. Numbered points represent last digit of year of study; arrows color-coded by year and indicate timing of Knack application.
Nearly 1500 eggs were marked and examined in field and laboratory-held bioassays for 2006 (Table 1 & 2). Unlike the anomalous 2005 and 2004 results where we saw a high rate of viability (i.e., low rates of egg inviability) that may have been a contributing factor to the explosive population growth seen after initial treatment, we saw background rates of inviability more typical of the past (Table 2); marginal rates for the UTC were ca. 28%. This is about average for our studies prior to this study (Naranjo & Ellsworth 2005). That is, there are generally very significant rates of background inviability of eggs in cotton during the summer. This return to more normal rates of inviability may have contributed to the sub-threshold status of the populations this past year.
Arizona Cotton Report (P-151) July 2007 173

Table 1. Summary egg (laboratory cohort) mortality statistics for 2004–2006 field studies in Maricopa, AZ.
Year Trt
2004 UTC
2005 UTC
2006 UTC
2004 Knack, 8 oz, by air
2005 Knack, 8 oz, by air
N %Inviable* %Live Schneider Abbott's
160
257
170
172
221
12%
18%
21%
67%
66%
84%
75%
48%
31%
32%
63.1%
58.3%
60.0%
63.4%
Marginal
(Inviable)
1 1.6%
18.1%
20.6%
65.5%
65.9%
2006 Knack, 8 oz, by air
2004 Knack, 8 oz, by ground
2005 Knack, 8 oz, by ground
314
173
235
70%
86%
62%
17%
13%
34%
61.9%
84.3%
54.0%
34.6%
83.0%
55.7%
69.7%
82.7%
60.9%
2006 Knack, 8 oz, by ground 200 82% 11% 76.7% 72.8% 80.8%
*%Inviable excluding "missing", "predation", and "dead 1st"; %Live includes these factors in N;
Marginal (inviable) rates corrected for missing and predation.
Marginal
(Insecticide)
54.2%
48.1%
47.5%
71.4%
43.0%
60.2%
Table 2.
Summary egg (field cohort) mortality statistics for 2004–2006 field studies in Maricopa, AZ.
Marginal Marginal
Year T rt
2004 UTC
N
400
%Inviable %Live Schneider Abbott's
11% 49%
(Inviable)
9.8%
(Predation)
6.6%
2005 UTC
2006 UTC
2004 Knack, 8 oz, by air
2005 Knack, 8 oz, by air
2006
2004
Knack, 8 oz, by air
Knack, 8 oz, by ground
2005 Knack, 8 oz, by ground
2006 Knack, 8 oz, by ground
334
179
329
272
333
318
247
232
4%
28%
56%
68%
68%
86%
77%
87%
59%
34%
23%
21%
17%
8%
15%
6%
49.9%
66.3%
55.2%
83.8%
76.2%
82.0%
61.2%
70.6%
5.0%
87.2%
81.7%
75.0%
4.4%
27.7%
49.2%
67.8%
67.6%
77.6%
77.2%
86.2%
8.4%
37.6%
2.0%
5.8%
32.3%
5.0%
6.0%
35.2%
*%Inviable excluding "missing", "predation", and "dead 1st"; %Live includes these factors in N;
Marginal (Inviable) rates corrected for missing and predation; Marginal (Predation) rates corrected for missing.
Marginal
(Insecticide)
38.6%
63.7%
43.3%
67.3%
73.0%
60.5%
Buckeye
At Buckeye (2006), populations reached threshold consistent with average trends for the area (Fig. 5), and like the year before, plant growth was again somewhat delayed over historical averages. The first and only insecticide spray was made on 13 July. Populations did continue to increase and the UTC began to show extreme signs of whitefly damage
(i.e., excess sugars and sooty mold growth on leaves). The treated plots and this field would be characterized as very well controlled with very little risk for stickiness, despite pressures seen in the UTC exceeding 2–3 large nymphs per disk, a very high level any time but particularly difficult in mid-July.
Over 1800 eggs were marked and examined in field and laboratory-held bioassays (Table 3 & 4). Unlike Maricopa, background rates of inviability were much lower (i.e., in the UTC). In addition, rates of missing eggs and preyed upon eggs were lower at the Buckeye location, similar to what was observed in 2005 and 2004. The result was a higher survival rate in the UTC and again significant capacity for the population to grow. The Maricopa population never had this capacity. Nonetheless, even at Buckeye, frequent monsoonal storms in 2006 helped to mitigate numbers throughout the test. While the UTC remained quite high by the end of our sampling interval (>3 large nymphs / disk), populations were much reduced towards the end of the season. The grower elected never to spray the UTC plot areas.
Table 3.
Summary egg (laboratory cohort) mortality statistics for 2004–2006 field studies in Buckeye, AZ.
Mar ginal Mar ginal
(Insecticide) Year Trt
2004 UTC
2005 UTC
2006 UTC
2004 Knack, 8 oz, by air
2005 Knack, 8 oz, by air
N
30
265
472
33
355
%Inviable*
18%
22%
12%
77%
66%
%Live
47%
66%
68%
18%
29%
Schneider
72.0%
56.1%
Abbott's
57.1%
38.6%
(Inviable)
11.5%
21.8%
12.1%
74.1%
64.6%
2006 Knack, 8 oz, by air 441 50% 35% 43.5% 52.0% 50.2%
*%Inviable excluding "missing", "predation", and "dead 1st"; %Live includes these factors in N;
Mar ginal (inviable) rates corrected for missing and predation.
61.9%
43.1%
36.9%
Arizona Cotton Report (P-151) July 2007 174

Table 4. Summary egg (field cohort) mortality statistics for 2004–2006 field studies in Buckeye, AZ.
Year
2004
2005
T rt
UTC
UTC
N
89
296
%Inviable*
8%
21%
%Live
69%
70%
Schneider Abbott's
Mar ginal
(Inviable)
7.5%
21.1%
Mar ginal
(Predation)
6.9%
4.3%
2006 UTC
2004
2005
Knack, 8 oz, by air
Knack, 8 oz, by air
510
70
358
7%
68%
78%
66%
20%
17%
65.6%
72.6%
77.0%
65.6%
6.9%
66.7%
75.8%
2006 Knack, 8 oz, by air 435 65% 25% 62.7% 68.1% 65.3%
*%Inviable excluding "missing", "predation", and "dead 1st"; %Live includes these factors in N;
15.7%
6.3%
2.9%
19.6%
Mar ginal (Inviable) rates corrected for missing and predation; Marginal (Predation) rates corrected for missing.
Mar ginal
(Insecticide)
57.9%
53.1%
58.3%
14
14
12
K K
K
K
12
10
10 8
6
8
6
4
2
C
0
14-Jul
O
I
4
2
3.5
O
3
I
C
I
I
0
2.5
k
3.5
1.5
3
2.5
1
I C
0.5
0
14-Jul o
I k
K
C
I
O
I
14-Aug
I
K
C
I
I k
C o
I o
14-Aug
C I k
I
14-Sep
O
I
O
I
C
14-Aug
I o
14-Sep
2
1.5
1
C
I
0.5
0
14-Jul o k
I
I
C Courier
K Knack k
O
Oberon o
UTC
Sprays
Intruder
I
14-Sep
5
4.5
4
C
5
4.5
3.5
3
4
2.5
2
1.5
1
0.5
0
14-Jul
N
3.5
k
I o k
3
2
1.5
C
I
I k
C o k o
I o
14-Aug k
I o
12
1
I
0.5
10
8
6
4
2
0
14-Jul
I o
10
I o
8
0
14-Jul
N
12
I
C
I C o
14-Aug
I k
I
C o
I o
14-Sep o
I
14-Aug o
I
I
14-Sep
I o
14-Sep
6
C k
4 k o
C
I
I
I
C o o k
2
I
I o
I
I C k
C o
I o
I o
14-Aug 14-Sep
0
14-Jul 14-Aug
Figure 5.
Population dynamics (eggs, small nymphs, large nymphs per disk, and adults per leaf) of whiteflies at the Buckeye commercial location, where four different compounds were sprayed once.
o
I
14-Sep
Wellton
The 2006 Wellton location was the earliest planted site and required initiation of sprays on 27 June. Over 800 eggs were bioassayed at this location (Table 5 & 6). This site had low marginal rates of predation, similar to rates observed in 2005 and 2004, significantly lower than the Buckeye and Maricopa sites. The entire site was under a large amount of water stress (due to lack of water and root-pruning from a recent cultivation) and competition from weeds at the initiation of this trial. This may have impacted the quality of our bioassays. The pest control advisor (PCA) had treated the southeastern portion of our test with Lorsban ® several weeks before trial initiation. Because the PCA elected to overspray the entire trial with a full rate of endosulfan, we are not able to adequately assess the progress of the control interval possible with the array of chemistry tested. The PCA was concerned about Lygus and pink bollworm levels
Arizona Cotton Report (P-151) July 2007 175

in our test fields, as well as whiteflies in the remaining fields, which had not been sprayed at the same time as our initiation of our trial.
Table 5.
Summary egg (laboratory cohort) mortality statistics for 2004–2006 field studies in Wellton, AZ.
Marginal Marginal
(Insecticide) Year Trt
2004 UTC
N %Inviable* %Live Schneider Abbott's
71 14% 76%
(Inviable)
13.6%
2005 UTC
2006 UTC
2004 Knack, 8 oz, by air
191
130
91
15%
12%
60%
69%
71%
38% 35.2%
77.4%
15.2%
15.3%
12.4%
63.4%
2005 Knack, 8 oz, by air
2006 Knack, 8 oz, by air
176
185
78%
49%
16%
42%
53.1%
74.4%
41.4%
77.8%
48.7%
*%Inviable excluding "missing", "predation", and "dead 1st"; %Live includes these factors in N;
Marginal (inviable) rates corrected for missing and predation.
49.3%
61.4%
36.5%
Table 6.
Summary egg (field cohort) mortality statistics for 2004–2006 field studies in W ellton, AZ.
Mar ginal Mar ginal
Year T rt
2004 UTC
2005 UTC
2006 UTC
2004 Knack, 8 oz, by air
2005 Knack, 8 oz, by air
N
267
271
238
298
198
%Inviable*
13%
10%
12%
64%
78%
%Live
71%
70%
61%
30%
17%
Schneider
58.4%
75.7%
Abbott's
52.4%
82.7%
(Inviable)
12.0%
9.4%
1 1.7%
60.6%
77.1%
(Predation)
5.1%
1.8%
7.4%
4.4%
0.6%
2006 Knack, 8 oz, by air 252 49% 37% 41.8% 35.4% 48.6%
*%Inviable excluding "missing", "predation", and "dead 1st"; %Live includes these factors in N;
8.6%
Mar ginal (Inviable) rates corrected for missing and predation; Marginal (Predation) rates corrected for missing.
Mar ginal
(Insecticide)
49.0%
67.1%
37.5%
Marana
This site was evaluated only once in 2004 during the three period of this study (Tables 7 & 8). Marana had comparative marginal rates for the other three sites evaluated that same year.
Table 7.
Summary egg (laboratory cohort) mortality statistics for 2004 field studies in Marana, AZ.
Marginal
Year Trt N %Inviable* %Live Schneider Abbott's (Inviable)
2004 UTC
2004 Knack, 8 oz, by air
36
81
11%
93%
86%
4% 92.1% 90.3%
11.4%
50.0%
*%Inviable excluding "missing", "predation", and "dead 1st"; %Live includes these factors in N;
Marginal (inviable) rates corrected for missing and predation.
Marginal
(Insecticide)
38.8%
Table 8.
Summary egg (field cohort) mortality statistics for 2004 field studies in Marana, AZ.
Marginal Marginal
Year T rt N %Inviable* %Live Schneider Abbott's (Inviable)
2004 UTC
2004 Knack, 8 oz, by air
186
310
12%
81%
58%
13% 78.5% 61.7%
11.1%
77.4%
*%Inviable excluding "missing", "predation", and "dead 1st"; %Live includes these factors in N;
(Predation)
4.5%
2.2%
Marginal (Inviable) rates corrected for missing and predation; Marginal (Predation) rates corrected for missing.
Marginal
(Insecticide)
67.1%
Nymph Mortality
The nymph mortality at each site for this three year period was evaluated in bioassays held in the lab (Tables 9–
12). Background rates of nymphal mortality tend to be very high (i.e., in the UTC). The specific reasons for this are unknown, but may in part relate to the bioassay conditions such as poor leaf quality, handler technique, etc.
Nevertheless, higher rates of survival were observed in 4 th instar nymphal bioassays (data not shown), even in the
Knack regimes. Presumably, nymphal development was too advanced and Knack delivered too late to impact these fourth instars directly.
The high rates of nymphal inviability bias the corrected estimates of insecticide mortality greatly. With high rates of
Arizona Cotton Report (P-151) July 2007 176

nymphal mortality in the UTC, it is difficult to assess the mortality in the Knack regimes. In Buckeye, we noted a large fraction of the nymphal population that resulted in eclosed, yet dead adults. This seemed to occur at slightly higher rates in the Knack treatment. However, these were counted as survivors and may have been in part responsible for the abnormally low rates of corrected mortality observed for Knack. Higher sample sizes or improved bioassay conditions may be necessary to increase detection of susceptibility changes.
Table 9.
Summary nymph mortality statistics for 2004–2006 field studies in Maricopa, AZ.
Y ear Trt N %Inviable Schneider Abbott's
2004
2004
Knack
Knack, 8 oz, by ground
216
101
84.7%
99.0%
82.3%
98.9%
63.3%
98.9%
67.8% 64.4% 2004
2004
2005
2005
2005
2005
Knack, 8 oz, by air
UTC
Knack
Knack, 8 oz, by ground
Knack, 8 oz, by air
UTC
104
115
330
102
153
177
72.2%
13.5%
99.4%
100.0%
98.9%
91.2%
93.1%
100.0%
87.2%
77.8%
100.0%
77.8%
2006
2006
2006
2006
Knack
Knack, 8 oz, by ground
Knack, 8 oz, by air
UTC
258
87
171
58
98.8%
98.9%
98.8%
89.7%
88.8%
88.9%
88.7%
50.0%
83.3%
66.7%
Table 10.
Summary nymph mortality statistics for 2004–2006 field studies in Buckeye, AZ.
Year
2004
2004 UTC
Trt
Knack, 8 oz, by air
N
34
26
%Inviable
100.0%
61.5%
Schneider
100.0%
Abbott's
100.0%
96.4% 95.2% 2005
2005
2006
2006
Knack, 8 oz, by air
UTC
Knack, 8 oz, by air
UTC
190
143
184
179
99.5%
85.3%
87.5%
82.7%
27.8% 25.8%
Table 11. Summary nymph mortality statistics for 2004–2006 field studies in W ellton, AZ.
Y ear Trt N %Inviable Schneider Abbott's
100.0% 100.0% 2004
2004
2005
Knack, 8 oz, by air
UTC
Knack, 8 oz, by air
50
56
163
100.0%
33.9%
97.5% 96.5% 95.8%
2005
2006
2006
UTC
Knack, 8 oz, by air
UTC
136
72
57
30.1%
94.4%
54.4%
87.8% 84.6%
Table 12. Summary nymph mortality statistics for 2004 field studies in Marana, AZ.
Y ear
2004
2004
Trt
Knack, 8 oz, by air
UTC
N Rows
20
26
%Inviable
90.0%
30.8%
Schneider
85.6%
Abbott's
88.9%
Estimates of Direct Knack Effects on Egg Viability
As noted previously, there are a number of ways one can assess the insecticidal action of Knack on egg survival in these studies. No one approach is “right”. However, the general trends can be examined comparatively over geographic locations and years. Studies by Naranjo & Ellsworth (2005; and unpubl. data) can be used as a historical reference standard for Knack performance. Life table data collected 1997–1999 was prior to any indications of susceptibility shifts to Knack in resistance bioassays performed by Dennehy et al. Calculated rates of insecticide mortality in eggs
(Table 13) were quite variable, although 1998 was considered an outlier year because of the extremely high rates of overall mortality that skew marginal calculations. That year aside, rates of Knack-insecticide mortality in eggs at the time of initial Knack application were ca. 40–60% on average. Our 2004–2006 studies place a similarly derived estimate for egg mortality at ca. 60–70% for the Maricopa site (Table 13). Note, direct comparisons to the other locations conducted in 2004 and 2005 are not possible because these sites had Knack applied aerially, whereas the previous work was all done under ground-applied conditions. However, under aerially-applied conditions, we can
Arizona Cotton Report (P-151) July 2007 177

examine any variations over regions and years in Table 14. In 2004, Maricopa had the lowest rate of egg mortality associated with Knack (ca. 38%) though not significantly lower than determined in the ground-applied trials done previously. In 2004, rates of egg mortality due to Knack were about 38–67%. The comparative rates in 2005 were in general much higher, ca. 53–67%, for each location. Within 2005, Buckeye had the lowest survival, yet the longest control interval. This underscores the dynamic nature of IGR-based (and other selective agents) control systems for whiteflies in cotton. That is, the control interval is some product of chemical and biological residual of the regime.
Interestingly, Dennehy et al. (data not shown) reported that the Buckeye location had the lowest susceptibility to pyriproxyfen after the 30 d field selection period in 2005 (i.e., from collections made > 30 DAT there). In 2006, rates were once again in the same range at about 37%–58%, somewhat lower than in 2005. Ironically, consultants and growers found 2006 to be a much easier year for controlling whiteflies (Ellsworth, unpubl. data).
Table 13.
Historical comparison of marginal rates of insecticide field egg mortality associated with Knack, Maricopa, AZ.
Trt 1997 1998 1999 2004 2005
Knack, 8 oz, by ground 0.5617
0.0929
0.3764
0.6400
0.7300
2006
0.6025
Table 14.
Geographic comparison of mar ginal rates of insecticide field egg mortality associated with Knack, 2004–06.
Trt
Knack, 8 oz, by air
Knack, 8 oz, by air
Knack, 8 oz, by air
Year
2004
2005
2006
Wellton
0.4898
0.6710
0.3750
Buckeye
0.5793
0.5311
0.5834
Maricopa
0.3857
0.6371
0.4330
Marana
0.6711
-
-
Because of the complex relationship of insecticide-related mortality with other sources of mortality in the field under the Knack regime, it is informative to also examine the insecticide-isolated mortalities identified in the laboratoryhoused bioassays (Table 15). In 2006, Schneider’s corrected mortalities due to Knack show Wellton and Buckeye as being very similar around 42% and Maricopa with somewhat higher mortality. Abbott’s corrected mortalities are less stable because of unequal sample sizes in these studies. Compared to 2005, egg mortality due directly to Knack insecticide was lower at Wellton and Buckeye, and the same or somewhat higher in Maricopa (for ground and air, respectively) in 2006. In 2004, the Buckeye and Wellton sites had higher egg mortality than their 2006 counterparts
(Table 15). Mortalities for both ground and aerial application at Maricopa for 2004 were greater than what was observed in 2006. Furthermore, the Marana site had the highest level of mortality overall when compared to all other sites evaluated both geographically and historically. The control interval in the field was very long for both Buckeye and Maricopa.
Table 15.
Geographic comparison of Schneider (left) and Abbott's (right) corrected rates of insecticide egg mortality directly measured (lab cohort) for Knack, 2004-06.
Trt
Knack, 8 oz, by air
Year
2004
Knack, 8 oz, by ground 2004
Wellton
0.5307
-
Buckeye
0.7198
-
Maricopa
0.6313
0.8430
Marana
0.9212
-
Wellton Buckeye Maricopa Marana
0.3519
0.5714
0.6000
0.9032
0.8296
-
Knack, 8 oz, by air 2005 0.7442
Knack, 8 oz, by ground 2005 -
Knack, 8 oz, by air 2006 0.4143
Knack, 8 oz, by ground 2006 -
0.5605
-
0.4351
-
0.5830
0.5398
0.6186
0.7672
-
-
-
0.7744
-
0.1522
-
0.3864
-
0.5202
-
0.6340
0.5567
0.3457
0.7284
-
-
-
-
Resistance Monitoring Data
Dr. Tim Dennehy’s laboratory was responsible for all resistance monitoring in this project (Table 16–18). Based on historical trends, their data would suggest that a significant shift in bioassay response of Arizona’s whitefly populations occurred several years ago. Specifically, at 0.1 μg concentration of pyriproxyfen, egg mortalities were originally in the 90+% range. More recently, the response at this concentration declined to around 60%. The suggestion is that resistance levels increased to this point. Further selection as was seen in the 2004 data from this project seemed to push mortalities as low as 40% or so for this concentration.
In 2006 in Maricopa (Table 16), the average pre-treatment response at this critical concentration was 63%. The posttreatment levels in the UTC were reduced by ca. 13%, whereas the reductions were ca. 15% in the aerial Knack treatment. However, the level of mortality increased post-treatment in the ground Knack treatment by about 13%.
Arizona Cotton Report (P-151) July 2007 178

Overall, there was almost no change pre- and post-treatment at this site.
In Buckeye this year (Table 17), the initial response in the pre-treatment plots was around 63%, same as measured at
Maricopa. After treatment, the UTC showed a decline in response of around 9%, while the Knack treatment showed a decline by about 12%. The average for this site post-treatment was around 56%, and seems rather similar to the pretreatment response.
At Wellton this year (Table 18), the mortality at this concentration of pyriproxyfen was very high, perhaps as high as we have seen in the past three years. The pre-treatment average response was around 91%, well above the Maricopa and Buckeye sites. Post-treatment, the UTC declined by nearly 5% and the Knack treatment by nearly 12%. The average post-treatment was around 83%, well above the pre-treatment levels seen at the other sites.
Overall, the declines in susceptibility from pre- and post-treatment samples, whether they were from the UTC or the Knack-treated plots, did not seem to be large or consistent with a Knack-associated trend. Interestingly, the highest susceptibilities in this year’s resistance monitoring data (i.e., for Wellton) were associated with the lowest measurements for performance monitoring (Tables 14 and 15).
Table 16. Summary of mortalities (% ± sd) for 2006 pyriproxyfen resistance monitoring data, Maricopa, AZ.
Pre-Treatment Post-Treatment
Trt
UTC
UTC
Knack8ozA
Knack8ozA
Knack8ozG
Knack8ozG
Field Rep
Rep 3
Rep 4
Rep 3
Rep 4
Rep 3
Rep 4
Conc.
0
0.1
1
10
0
0.1
1
10
0
0.1
1
10
0
0.1
1
10
0
0.1
1
10
0
0.1
1
10
Corrected
Mean
99.76
11.76
76.51
93.32
98.45
4.47
61.52
88.19
99.88
4.77
54.92
95.87
99.22
11.34
59.93
91.38
97.84
7.41
61.48
94.14
99.01
9.2
65.43
96.93
Corrected
StDev
0.58
12.18
9.71
4.17
2.41
3.35
4.58
5.69
0.28
4.74
24.87
5.3
1.25
6.41
13.18
3.05
4.29
3.88
7.53
2.09
0.71
7.77
11.83
3.05
Corrected
Mean
99.23
0.85
60.36
90.3
98.68
7.24
69.26
88.59
99.85
8.28
62.57
96.59
99.44
6.81
60.73
83.62
98.34
3.14
43.61
86.64
97.43
2.68
58.91
88.09
Corrected
StDev
1.47
1.47
10.56
5.15
1.2
5.51
7.72
10.03
0.36
2.62
20.8
2.6
1.15
4.47
11.68
9.02
1.94
3.3
10.2
1.88
0.93
2.4
5.49
5.81
From Dennehy & DeGain, unpubl. data
Arizona Cotton Report (P-151) July 2007 179

Table 17. Summary of mortalities (% ± sd) for 2006 pyriproxyfen resistance monitoring data, Buckeye, AZ.
Pre-Treatment Post-Treatment
Trt Conc.
Corrected
Mean
Corrected
StDev
Corrected
Mean
Corrected
StDev
UTC
UTC
Knack8ozA
Knack8ozA
Rep 1
Rep 2
Rep 1
Rep 2
0
0.1
1
10
0
0.1
1
10
0
0.1
1
10
0
0.1
1
10
8.47
65.66
94.86
99.31
10.72
57.6
93.58
99.64
6.71
63.65
95.93
99.82
6.54
64.48
92.84
99.84
7.35
8.04
2.91
1.07
5.49
12.28
3.4
0.63
4.72
11.12
1.6
0.45
5.42
13.59
3.42
0.39
8.25
54.25
83.83
99
4.71
57.51
86.72
98.86
2.16
57.11
90.44
98.61
4.64
55.85
91.4
99.44
8.79
7.28
15.87
1.88
3.93
10.49
11.82
1.5
2.04
13.23
4.85
1.76
9.11
19.8
8.66
0.87
From Dennehy & DeGain, unpubl. data
Table 18. Summary of mortalities (% ± sd) for 2006 pyriproxyfen resistance monitoring data, Wellton, AZ.
Pre-Treatment Post-Treatment
Trt Conc.
Corrected
Mean
Corrected
StDev
Corrected
Mean
Corrected
StDev
UTC
UTC
Knack8ozA
Knack8ozA
Rep 1
Rep 2
Rep 1
Rep 2
0
0.1
1
10
0
0.1
1
10
0
0.1
1
10
0
0.1
1
10
8.91
88.48
97.28
100
11.83
93.51
98.78
100
8.96
91.14
99.53
99.51
7.72
89.76
96.16
100
5.19
6.37
3.1
0
7.64
2.09
1.74
0
7.1
5.67
0.85
1.19
4.86
5.76
2.8
0
7.45
85.99
92.03
99.9
8.19
87.4
97.54
99.76
1.93
77.73
96.73
99.15
6.31
81.92
98.01
99.3
3.62
8.54
2.45
0.25
6.47
10.07
5.05
0.59
1.66
6.09
4.37
2.08
6.1
6.03
3.21
0.96
From Dennehy & DeGain, unpubl. data
Conclusions
What a difference a year makes! In 2005, most pest managers struggled to gain control over their whitefly populations in cotton. It would be under these conditions of extreme pressure that we would expect various product complaints including claims of resistance. Our work last year seemed to indicate that performance parameters for Knack and resistance parameters for pyriproxyfen were well within the range expected for the last several years. Further, these levels should have translated to more or less “normal” performance of the product. However, operational barriers to the performance of Knack and other chemistry were in play. Late planting conditions, lush winter vegetation capable of hosting whiteflies, poor growing conditions, and an extended period of extreme immigration pressure were all factors that diminished the impact of Knack and many other products in 2005.
Arizona Cotton Report (P-151) July 2007 180

In 2006, the preceding winter was among the driest on record with over 180 d without moisture. Late planted conditions were common, though perhaps not as late as in 2005. Crop growth conditions were also marginal for some mid-summer.
However, a very active monsoon season delivered regular storms, both dry and wet, all season long in central Arizona.
These conditions of high winds and dust movement helped to continually lower whitefly populations. In addition, and for some of the same reasons, Lygus densities were among the lowest ever seen in Arizona. This translated into very few sprays against this pest statewide. Also, central and eastern Arizona were under a new pink bollworm eradication program. As a result, Bt cotton was adopted on a much wider acreage (ca. 94.6% v. historic levels closer to 80% for this area). No early sprays were needed on these acreages for pink bollworm. These suspended broad-spectrum Lygus and pink bollworm sprays provided for a very hospitable environment for beneficial arthropods. Their activity was evident in most central Arizona fields this year, in contrast to 2005 when levels of natural enemies were lower or at least much later to develop than in 2006.
In the absence of these objective measures, it would be easy for a grower to “blame” or credit a product’s performance in these situations. In 2005, there was more “blame” and in 2006 there is likely more “credit” to distribute. Our objective measures of Knack performance and of pyriproxyfen resistance seem to be conveying a consistent message.
Not much has changed among the years or locations studied thus far. What levels of performance we have measured have been similar throughout the study period thus far. The resistance data have also failed to point to a consistent or additional change in susceptibility as the result of Knack field applications. Thus, barring all the other external operational and environmental factors at work, we would have expected similar intervals of control in each year. Yet, observed intervals have been different (e.g., 2005 vs. 2006) and this fact points to the importance of these external factors in assessing product performance or in inferring potential resistance issues.
Work will continue in 2007 to identify factors that contribute to whitefly outbreak conditions and errors in estimating population densities. In addition, we will continue these performance-monitoring studies to identify conditions where
Knack performance is reduced and/or where susceptibilities are in significant decline based on resistance monitoring data. In these cases, these data will be key to understanding these performance changes, i.e., either due to operational factors mentioned above or due to innate changes in whitefly susceptibility. These data will be important in advising growers about the risk factors associated with whitefly outbreaks and should lead to recommendations for minimizing these risks.
Acknowledgments
We gratefully acknowledge funding from ACGA, ACRPC, and Valent. In particular thanks to Todd Mayhew, Art
Anderson and Jeff Smith (Valent); Larry Antilla (ACRPC); and Bob Nichols (CI). The authors wish to express their appreciation to our grower and PCA cooperators Matt Philips, Greg Hogue, John Boelts, Gary Mayfield, Rick
Ladra, Chess Haley, Clint Osborn, and Jim Osborn. Thanks also to MAC & USDA personnel Francisco Borjorquez,
Marion Borjorquez, Vianey Borjorquez, Korrina Duffy, Kristen Duffy, Adam Gibson, Matt Hagler, Jose Luis Partida,
Andreanna Thacker, Julianne Trejo, and Bailey Stuart.
References
Diehl, J.W., P.C. Ellsworth & S.E. Naranjo. 1997. Whiteflies in Arizona No. 11: Binomial Sampling of Nymphs. The
University of Arizona, Cooperative Extension. 2 pp. URL: http://ag.arizona.edu/crops/cotton/insects/wf/wfly11.pdf
Ellsworth, P.C., J.W. Diehl, T.J. Dennehy, and S.E. Naranjo. 1995. Sampling Sweetpotato Whiteflies in Cotton.
IPM Series No. 2. Publ. No. 194023. University of Arizona, College of Agriculture and Life Sciences, Cooperative
Extension, Tucson, Arizona. URL: http://cals.arizona.edu/crops/cotton/insects/wf/wfsampl.html
Ellsworth, P.C., T.J. Dennehy, and R.L. Nichols. 1996a. Whitefly Management in Arizona, 1996. IPM Series No. 3.
Publ. No. 196004. University of Arizona, College of Agriculture and Life Sciences, Cooperative Extension, Tucson,
Arizona. URL: http://cals.arizona.edu/crops/cotton/insects/wf/cibroch.html
Arizona Cotton Report (P-151) July 2007 181

Ellsworth, P.C., J.W. Diehl, and S.E. Naranjo. 1996b. Sampling Sweetpotato Whitefly Nymphs in Cotton. IPM Series
No.6. Publ. No. 196006. University of Arizona, College of Agriculture and Life Sciences, Cooperative Extension,
Tucson, Arizona. URL: http://cals.arizona.edu/crops/cotton/insects/wf/ipm6.html
Ellsworth, P.C., R. Tronstad, J. Leser, P.B. Goodell, L.D. Godfrey, T.J. Henneberry, D. Hendrix, D. Brushwood, S.E.
Naranjo, S. Castle, and R.L. Nichols. 1999. Sticky Cotton Sources & Solutions . IPM Series No. 13. Publ. No.
AZ1156. University of Arizona, College of Agriculture and Life Sciences, Cooperative Extension, Tucson, Arizona. 4 pp. URL: http://cals.arizona.edu/crops/cotton/insects/wf/stickycss.pdf
Ellsworth, P.C. & J.L. Martinez-Carrillo. 2001. IPM for Bemisia tabaci in North America: A Case Study. In S. E.
Naranjo and P. C. Ellsworth (Eds.), Special Issue: Challenges and Opportunities for Pest Management of Bemisia tabaci in the New Century. Crop Protection 20: 853–869.
Ellsworth, P.C., J.C. Palumbo, S.E. Naranjo, T.J. Dennehy, and R.L. Nichols. 2006. Whitefly Management in Arizona
Cotton 2006. IPM Series 18. Publ. No. AZ1404. University of Arizona, College of Agriculture and Life Sciences,
Cooperative Extension, Tucson, Arizona. 4 pp. URL: http://cals.arizona.edu/pubs/insects/az1404.pdf
Naranjo, S. E. & D. Akey. 2005. Conservation of natural enemies in cotton: Comparative selectivity of acetamiprid in the management of Bemisia tabaci. Pest Manage. Sci. 61: 555-566.
Naranjo, S.E. & P.C. Ellsworth. 2005. Mortality dynamics and population regulation in Bemisia tabaci. Entomologia
Experimentalis et Applicata. 116: 93-108.
Palumbo, J.C., Horowitz, A.R. and Prabhaker, N. 2001. Insecticidal control and resistance management for Bemisia tabaci. In S. E. Naranjo and P. C. Ellsworth (Eds.), Special Issue: Challenges and Opportunities for Pest Management of Bemisia tabaci in the New Century. Crop Protection 20(9): 739-765.
Palumbo, J.C., P.C. Ellsworth, T.J. Dennehy, and R.L. Nichols. 2003. Cross-Commodity Guidelines for Neoneonicotinoid
Insecticides in Arizona. IPM Series 17. Publ. No. AZ1319. University of Arizona, College of Agriculture and Life
Sciences, Cooperative Extension, Tucson, Arizona. 4 pp. URL: http://cals.arizona.edu/pubs/insects/az1319.pdf
Arizona Cotton Report (P-151) July 2007 182