C.Q. Ruan C. Sengonca  B. Liu
Prey consumption of Geocoris ochropterus in response
to prey densities, stages and species
Abstract Geocoris ochropterus is polyphagous predatory bug abundant in vegetable field of
southern China. It is a new promising biological control agent against pest thrips Frankliniella
occidentalis. But little is known about its response to the change in prey density and to the
coexistence of different prey ages as well as different prey species. Therefore, the present
research focused on the prey consumption of G. ochropterus with changing number of F.
occidentalis offered as prey, and its preference for different stages of F. occidentalis as well as
for different prey species. All experiments were carried out at a constant temperature of 25 oC
under laboratory conditions. The results showed that G. ochropterus adapted smoothly to
fluctuating prey availability. The mean daily prey consumption was higher at a prey density of
50 L2 of F. occidentalis than at 10 or 5 L2/day. In contrast, most individuals in lower prey
densities were killed. As all prey densities were changed to 30 L2/day, the prey consumption
decreased in the trial where the prey density was previously 50 L2/day before change, while a
considerable increase in prey consumption was noted in the other trials where the prey density
was previously 10 or 5 L2/day before change. When exposed to the mixture of L1, L2 and
female adults of F. occidentalis, N2 instar of G. ochropterus, after having molted for 3 days,
preferred adult thrips to the larval ones. It daily consumed a mean of 1.0-1.2 L1, 0.9-1.1 L2
and 2.3-2.9 adult thrips per predator. N4 and female adults of G. ochropterus also preferred the
adult of F. occidentalis. The mean daily prey consumption was 1.2-3.2 L1, 2.8-5.1 L2 and
Ruan  C. Sengonca ()
Department of Entomology and Plant Protection,
INRES-Phytomedicine, University of Bonn,
Nussallee 9, 53115 Bonn, Germany
E-mail: C.Sengonca@uni-bonn.de
C.Q.
B. Liu
Institute of Agro-Biological resources,
Fujian Academy of Agricultural Sciences,
Fuzhou, Fujian, 350003, China
3.8-11.6 adult thrips by N4, while 4.8-6.1 L1, 6.5-10.6 L2 and 18.1-30.1 adult thrips by the
predatory adult. The experiments on prey-species preference, where F. occidentalis (♀),
Thrips tabaci (♀), Bemisia tabaci (puparia), Aphis gossipii (1-2 days old) and Tetranychus
urticae (♀) were offered together as prey, revealed that G. ochropterus of all the tested stages
significantly preferred the two thrips species. The N2 predator consumed a daily mean of
2.2-3.7 T. tabaci and 1.2-2.8 F. occidentalis, while it only killed 0.5-1.7 T. urticae, 0.3-1.1 B.
tabaci and 0.1-0.2 A. gossipii in the trials. N4 and female adult of G. ochropterus consumed a
daily mean of 4.6-7.9 and 8.7-9.9 individuals from each thrips species, respectively. In
contrast, they killed a daily mean of only 0.0-1.4 individuals from B. tabaci or A. gossypii.
The predator preferred T. tabaci to F. occidentalis except that N4 showed no significant
difference between the two thrips species.
Keywords Geocoris ochropterus  Prey consumption  Frankliniella occidentalis  Thrips
tabaci
Introduction
The western flower thrips, Frankliniella occidentalis, originated in western North America
and has now spread to all continents, becoming a worldwide insect pest for greenhouse and
field crops (Tygges 1991, Karnkowski and Trdan 2002). It can infest about 219 plant species
belonging to 59 genera, which include vegetables and ornamental crops (Brdsgaard 1989,
van Dijken et al. 1994). F. occidentalis not only directly damage host plants by destructively
feeding on flowers, fruits and foliages, but also cause indirect damage by transmitting viral
pathogens to host plants (Stormsmm et al. 2002). Its occurrence usually leads to tremendous
loss of crops (Blaeser et al. 2004).
Managing F. occidentalis is challenging for several reasons. Short life cycle, high
reproduction and years of exposure to insecticides have made the thrips high resistant against
many insecticides (Frey 1990, Zhao et al. 1994; Kontsedalov et al. 1998). The pest thrips
preferring to live inside flower structures also reduces the efficacy of chemical control
program (Bene & Gargani 1989). In addition, the extensive use of pesticides can promote
negative impacts on human health and on ecosystems (Etienne et al., 1990). Therefore, it
seems promising to develop biological control methods using predators and parasitoids for
pest suppression.
Geocoris ochropterus (Heteroptera: Lygaeidae) is abundant in vegetable fields in southern
China. It is polyphagous predatory bug to prey pest species. However the knowledge of G.
ochropterus still lacks in literature. The author’s previous experiments showed that G.
ochropterus is a promising biological control agent against F. occidentalis. To use a predator
for a biological control program, some factors in agro-ecosystem must be taken into account.
In vegetable plantation, the population of a pest insect is changing with different instars
coexisting. In addition, there are naturally several pest species, which might serve as potential
prey for the predator. Accordingly, it is important to know the adaptation of G. ochropterus to
fluctuating prey availability, as well as its affinity toward a certain developmental stage of the
target pest and even the pest species.
Therefore, the present laboratory work was aimed to investigate the prey consumption of
G. ochropterus in response to a changing number of F. occidentalis offered as a prey, as well
as the predator’s affinity to prey stages and different pest species as prey in the laboratory.
Materials and methods
All insect rearing and experiments were conducted at 25±1 oC temperature, 60±10% RH, 16:8
h (L:D) photoperiod and a light intensity of about 4,000 lx.
Rearing of G. ochropterus was initiated with a few individuals, which were collected from
soybean plantation in Fuzhou City of the southern China. The stock culture was reared on
pepper plants, infested with F. occidentalis as a prey, in meshed cages (80×50×60 cm). For a
regular prey supply, pepper plants were replaced with fresh ones, infested with F. occidentalis
whenever needed.
Pest species, including F. occidentalis, Thrips tabaci, Bemisia tabaci, Aphis gossipii and
Tetranychus urticae, were obtained from the original stock cultures at the Institute of Crop
Science and Resource Conservation, University of Bonn, Germany. F. occidentalis was
exclusively reared on bean plants in an exclusive climatic chamber. T. tabaci was maintained
on onion plants in another climatic chamber. B. tabaci was kept on cucumber plants in a
meshed cage. A. gossipii and T. urticae were maintained on cotton and bean plants,
respectively.
In order to obtain the desired stages of G. ochropterus and the pest species for the
experiments, round Plexiglas cages (11 cm diameter× 3 cm height) were prepared for rearing
insect in incubators. The cages were partially filled with 0.5 cm thick agar gel layer and the
lid of each had three holes covered with mesh to allow aeration. To rear the desired stages of
G. ochropterus, the bean leaves, which infested with F. occidentalis of different life stages,
were placed upside down onto the agar gel layer in the Plexiglas cages. Thereafter, five
female and two male adults of G. ochropterus were transferred from the stock culture into
each of the Plexiglas cages. The cages then were kept in an incubator for G. ochropterus to lay
eggs at the same climatic condition as above. 24 h later, the adults were removed and the
newly laid eggs in the cages were reared until they reach the desirable life stages for
experiments. To acquire the desired stages of F. occidentalis, 20-30 female adults were
collected from the stock culture and transferred onto the bean leaves, which were placed with
upside down on the agar gel layer in the Plexiglas cages. The Plexiglas cages were then kept
in incubator for the thrips to lay eggs. After 24 h, the thrips adults were removed and the eggs
were kept for further development. To obtain the desired life stage of T. tabaci, the same
procedure as for F. occidentalis was used, except that the bean leaves were replaced with leek
leaves. To obtain the desired stage of A. gossipii, 20 female adults were picked up from the
stock culture and transferred onto the cucumber leaves, which were put upside down on the
agar gel layer in the round Plexiglas cages. The adult A. gossipii were removed after 24 h and
the newly laid nymphs in the cages were reared. To obtain uniformly aged B. tabaci,
cucumber plants were exposed to B. tabaci infestation in the stock culture cages for 12 h and
then incubated until the required stage for the experiments was reached. The desired stage
from T. urticae was identified under a binocular microscope on leaves obtained from the bean
plants in the stock culture of T. urticae.
All experiments were carried out in an arena, a round Plexiglas cage 3.6 cm in diameter
and 1.5 cm in height. They were partially filled with 0.5-cm-thick agar gel layer and the lid of
each had a hole covered with mesh to allow aeration.
A set of experiments were conducted to determine the prey consumption of G. ochropterus
with the changing number of F. occidentalis offered as prey. 7-day-old adult females of the
predator were used over a period of 3 weeks. Each female was placed singly on cucumber leaf
disc (3 cm in diameter) in the arenas and offered daily 50, 20, 10 or 5 L2 larvae of F.
occidentalis during the 1st experimental week. During the 2nd week of the experimental week,
the number of prey offered to each predator was changed to 30 L2 larvae/day, while in 3rd
experimental week it was 50, 20, 10 or 5 L2 larvae/day. The females of G. ochropterus were
transferred daily to new cages, containing the appropriated number of L2 larvae of F.
occidentalis. The number of consumed prey, which were emptied of fluid and easily
distinguished from those of natural mortality, was counted under a binocular microscope. All
the experiments were replicated ten times.
In the experiments to determine the preferred prey stage, N2, N4 and 10-day-old adult
females of G. ochropterus were observed. The predatory individuals were singly transferred
onto the cucumber leaf discs in the arenas. 30 individuals from each of L1, L2 and female
adults of F. occidentalis were offered together as prey. Afterwards, the arenas were kept in an
incubator at the same climatic condition as the above. The predatory individuals were
transferred daily to new arenas containing fresh prey stages of F. occidentalis. The number of
killed prey from the three stages was determined daily under a binocular microscope. The
experiments were conducted throughout the entire developmental period of N2 and N4 instars
and for three days with the adult females. Ten replications were set for the experiments.
In the experiments to investigate the preferred prey species by G. ochropterus, five pest
species such as F. occidentalis (♀), Thrips tabaci (♀), Bemisia tabaci (puparia), Aphis
gossipii (1-2 days old) and Tetranychus urticae (♀) were used as prey. To establish the
experiments, cucumber leaves infested with pupae of B. tabaci were excised to make leaf
discs (3 cm in diameter). The whitefly pupae on each leaf disc were removed with camel-hair
brush until 20 pupae were remained. The prepared leaf discs were placed upside down onto
the agar gel layers in the arenas, one leaf disc for one arena. 20 individuals from each of the
rest pest species were also transferred into each of the arenas. Thereafter, N2, N4 and
10-day-old adult females of G. ochropterus were singly introduced into the arenas. The
treatments were kept in an incubator at the same climatic condition as above. 24 h later, the
predatory individuals were transferred to new arenas containing fresh prey from the five
different species. The number of killed prey of each species was recorded. The experiments
were conducted throughout the entire developmental period of N2 and N4 instars and for three
days with the adult females. Ten replications were set for the experiments.
For the statistical comparison among several means, one-factor analysis of variance was
conducted. Significant differences were determined utilizing LSD test at p ≤ 0.05. t-test was
utilized for comparisons between only two means (Winstat 1996).
Results
Prey consumption by changing prey offer
Figure 1 shows the results of experiments on the prey consumption by female adults of G.
ochropterus, where a changing number of F. occidentalis at the second instar were offered as
prey. During the 1st week, when the daily prey offer was 50 thrips/day, a mean of 19.8-21.0
thrips/day were consumed. While a mean of 14.2-17.2 and 6.4-8.9 thrips/day were consumed
when 20 and 10 thrips/day were offered, respectively. Least prey consumption of 2.0-4.1
thrips/day was recorded when 5 thrips/day were offered.
The prey consumption decreased during the second experimental week in the trial, before
which 50 thrips/day had been offered. While in the other trials, before which 20, 10 and 5
thrips/day were offered, the prey consumption increased. Such increase was clearer in the
trials before which 5, 10 thrips/day were offered. During this week, the prey consumption by
a female adult of G. ochropterus was a mean ranging between 16.9 and 25.1 thrips/day.
In the 3rd experimental week, the daily prey offer was altered again to 50, 20, 10 and 5
thrips/day. In the first trial, with a daily prey offer of 50 thrips, an adult of G. ochropterus
consumed 19.3-24.7 thrips/day, considerably more than that during the week before. In the
other trials, the prey consumption showed remarkable decrease especially in the trials, in
which 10 and 5 thrips/day had been offered, where a mean of 5.8-8.3 and 2.1-4.2 thrips/day
were consumed by an predator, respectively.
50 larvae/day
30 larvae/day
Mean daily number of consumed F. occidentalis
30
25
20
15
10
5
0
7
9
11
13
20 larvae/day
30
25
20
15
10
5
0
7
9
11
7
9
11
13
7
9
11
19
21
15
17
19
13
15
17
19
21
15
17
19
25
27
23
25
27
10 larvae/day
21
30 larvae/day
13
23
20 larvae/day
30 larvae/day
5 larvae/day
30
25
20
15
10
5
0
17
30 larvae/day
10 larvae/day
30
25
20
15
10
5
0
15
50 larvae/day
23
25
27
5 larvae/day
21
23
25
27
Days after adult emergence
Fig. 1 Mean daily prey consumption by 7-day-old females of Geocoris ochropterus
with a changing number of the second instar larvae of Frankliniella occidentalis as
prey offer on cucumber leaf discs at 25±1 oC
Preference for different stages of Frankliniella occidentalis
Figure 2 illustrates the prey-stage preference by N2, N4 instars and 10-day-old female adults
of G. ochropterus with L1, L2 instars and female adults of F. occidentalis as prey. During the
first 3 days after molting, N2 instar of G. ochropterus showed no preference for life stages of F.
occidentalis. However, after having molted for 3 days, the predatory nymphs preferred adult
thrips to the larval prey, where they daily consumed a mean of 1.0-1.2 L1, 0.9-1.1 L2 and
2.3-2.9 adult thrips per predator. For N4 instar and female adults of G. ochropterus, the adult
of F. occidentalis was more preferred than the other two prey ages. The daily prey
consumption by the N4 nymphs was a mean of 1.2-3.2 L1, 2.8-5.1 L2 and 3.8-11.6 adult thrips.
It was 4.8-6.1 L1, 6.5-10.6 L2 and 18.1-30.1 adult thrips for a 10-day-old female adult of G.
ochropterus.
10
8
6
4
2
0
L1
L2
Adults
N2
Mean no. of consumed F. occidentalis
1
25
20
15
10
5
0
a
a
a
a
a
a
a
a
a
a
a
a
a
b
b
2
3
4
Developmental period of N2 (days)
5
N4
a
a
a
b
a
a
1
2
a
a
b
b
c
b
a
a
3
4
a
a
b
b
5
6
Developmental period of N4 (days)
40
32
24
16
8
0
Adult ♀♀
a
a
a
b
1
2
a
a
a
b
b
3
Days after ten days of adult emergence
( daysby) second instar (N2), fourth instar nymph (N4) and
Fig. 2 Prey consumption
10-day-old adult females of Geocoris ochropterus by feeding on first instar (L1),
second instar larvae (L2) and adult females of Frankliniella occidentalis as prey on
leaves of Phaseolus vulgaris at 25±1°C temperature.
Preference for different species of prey
Figure 3 represents the preference by N2, N4 and 10-day-old female adults of G. ochropterus
for different pest species: F. occidentalis (♀), T. tabaci (♀), B. tabaci (puparia), A. gossipii
(1-2 days old) and T. urticae (♀). All G. ochropterus stages tested significantly preferred F.
occidentalis and T. tabaci to the other three pest species. N2 instar of G. ochropterus showed a
significantly higher preference for T. tabaci over F. occidentalis. A daily mean of 2.2-3.7 T.
tabaci per predator and 1.2-2.8 F. occidentalis per predator was consumed. At the same time,
the predatory N2 nymphs daily consumed the other pest species with means of 0.5-1.7 T.
urticae, 0.3-1.1 B. tabaci and 0.1-0.2 A. gossipii per predator. When the predator was in N4
instar, it showed familiar preference for the both thrips species, consuming 4.6-7.9
thrips/predator. Meanwhile the predatory N4 daily consumed 2.5-4.3, 0.4-0.5 and 0.2-0.8
individuals/predator from T. urticae, B. tabaci and A. gossipii, respectively. When 10-day-old
female adults of G. ochropterus were used as predatory individuals, T. tabaci was more
preferred than F. occidentalis. The predatory adults daily consumed 9.0-9.9, 8.7-9.7, 4.7-6.1,
0.0-0.1 and 0.2-1.4 individuals/predator from T. tabaci, F. occidentalis, T. urticae, B. tabaci
and A. gossypii, respectively.
N2
8
a
ab
b
6
4
a
a
a
a
b
b
2
b
a
a
a
a
a
a
b
b
c
b
A. gossypii
B. tabaci
T. urticae
F. occidentalis
T. tabaci
a
a
a
b
b
0
Average daily no. of preys consumed
1
25
2
3
4
Developmental period (days)
N4
20
a
a
15
a
ab
c
10
5
c
5
a
a
b
b
b
b
c
c
c
c
c
c
c
c
a
b
0
1
30
25
20
2
3
4
5
Developmental period (days)
6
Adult ♀♀
b
a
c
15
d
10
5
d
a
a
b
b
c
c
d
d
0
1
2
3
Days after ten days of adult emergence
Fig. 3
Prey consumption by second instar (N2), forth intar (N4) and 10-day-old adult
females of Geocoris ochropterus by feeding on mixed population of 5 different
prey species offered together on leaves of cucumber leaf at 25±1°C temperature.
[Different small letters within the same bar indicate significant differences in the prey consumption
of the different prey species at p<5% (One-factor analysis of variance ).
Discussion
In the present experiments, it was shown that the examined predator, G. ochropterus, was able
to adapt to the fluctuation in prey availability. Its daily prey consumption increased with prey
density. But at lower prey density, the predator could kill most of the offered prey individuals.
Although the response of G. ochropterus to changing prey density was not previously
documented, its related species, G. punctipes, was reported to kill more eggs of cotton
bollworm (Helicoverpa zea) in relation to the prey density (Parajulee, et al 2006). The present
results also agree with Alvarado et al. (1997), who revealed that the prey consumption of
Dicyphus tamaninii increase until satiation as more prey individuals was offered. The
response of the entomophagous ladybird Serangium parcesetosum to fluctuating prey density,
which was reported by Sengonca et al. (2005), was in the same pattern as that of G.
ochropterus too.
G. ochropterus of the three tested stages were able to prey on each of L1, L2 and female
adults of F. occidentalis, which were simultaneously offered as prey in present studies.
However, all of them showed the preference for the adult over the larval of F. occidentalis,
except that the early second stage nymphs presented no prey-stage preference. There were no
previous studies on the preference of G. ochropterus for different stages of thrips. In its related
species, G. punctipes was also reported to showed preference for the adult whitefly over the
immature ones when the adult predator was exposed to a choice of different prey
stages(Hagler et al. 2004). But no more knowledge was available on prey-stage preference of
predatory species in genus Geocoris. On other predators of thrips, Nagai et al. (2000) reported
that preference between T. palmi adults and larvae changed with the development of Orius
sauteri. This is different from the prey-stage preference of G. ochropterus which was revealed
in present research.
Present research revealed that G. ochropterus predated all the five tested prey species with
apparent prey preference. F. occidentalis and T. tabaci were more preferred than the other
three prey species by all the tested predatory stages. Furthermore, G. ochropterus preferred T.
tabaci to F. occidentalis except it was in N4 stage, during which it showed no preference
between the two thrips species. In literatures, G. ochropterus was reported not only a predator
of some thrips (Kumarn et al. 1985) but also a predator of whitefly B. tabaci (Kapadia et al.
1991). In present research, the predatory bug predated the two prey species too. However, no
knowledge was available for the prey species preference of G. ochropterus. Hagler et al.
(2004) reported that another related predatory bug, G. punctipes, also showed a significant
preference when it was expose to a choice of Lygus hesperus, A. nerii, Heliothis zea, H.
virescens and Spodoptera exigua as preys. Another research indicated that G. punctipes
preferred T. urticae to A. gossipii (Silvia et al. 2004). In present research, G. ochropterus also
preferred T. urticae to A. gossipii as well as B. tabaci, except that the predator was in N2 stage
when it showed no preference for prey species.
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