Effect of Certain Cucumber Varieties on the Biology of Aphis gossypii (Homoptera : Aphididae). By Nashat A. Hafiz Ali Abstract. Development, reproduction, and population growth parameters of the melon aphid, Aphis gossypii (Glover), on seven cucumber varieties were evaluated under greenhouse conditions. Melon aphids had faster nymphal development on Tamra 761, Rawa- F1- RS and F1hybrid Beit alpha MR (5.2, 5.4 and 5.4 d) respectively, compared with the other varieties (5.8 6.1 d). Aphids reared on Rawa- F1- RS had the highest fecundity (59.3 offspring/aphid) and daily reproduction (3.8 offspring/aphid/day). The net reproductive rate (50.4 offspring/aphid/generation) on Rawa- F1- RS was 18 %, 25 %, 38 %, 10 %, 35 %, and 47 % higher and the population doubling time (2.31d) was 7 %, 25 %, 15 %, 15 %, 10 %, and 11 % faster than those parameters on Beit alpha MR, F1- hybrid Beit alpha MR, Beth alpha MR, Beth alpha MR hybrid, Hezera 480, and Tamra 761, respectively. The intrinsic rate of increase indicated that a population of 10 females of A. gossypii could increase to become 59, 66, 66, 59, 53, and 77 individuals on Beth alpha MR, Tamra 761, Hezera 480, Beth alpha MR hybrid, Beit alpha MR, F1- hybrid Beit alpha MR, and Rawa- F1- RS, respectively. Key words: melon aphid, life table, population growth, cucurbits The melon aphid, Aphis gossypii (Glover), is a serious pest of cucumber plants in Egypt. This aphid causes economic damage to cucumber plants by direct injury to the plants and vectors viral diseases, such as CMV. At present, insecticides are relied upon for control of aphids in cucumber. The use of insect resistant varieties has been a major successful control tactic against vegetable pests, often resorted to because of the difficulty of using pesticides on these edible plants (Chambliss and Jones, 1966; Da Costa and Jones, 1971a; Hafiz and Hagag, 1997; Howe et al., 1976; Kooistra, 1971). Knowledge of host plant effects on the biological parameters of the melon aphid is essential for population dynamics studies. Consequently, experiments were conducted to examine the effects of seven cucumber varieties on the development, longevity, and reproduction of melon aphid collected in Assuit, Egypt. Materials and Methods Aphid source. Laboratory colonies of melon aphid were established with field-collected aphids from cucumber and cotton plants. The colonies were maintained on potted seedlings of cucumber plants in an environmental chamber (maintained at 25 ± 2 0C and 70 ± 5% RH) at the A.R.E. Egypt, Assuit, Insect Research Laboratory. Experimental procedures. Seven cucumber varieties, Cucumis sativus L., were used for the experiments: F1- hybrid Beit alpha MR, Beit alpha MR, Beth alpha MR F1- hybrid, Beth alpha MR, Rawa- F1- RS, Hezera 480, and Tamra 761. The cucumber varieties were grown under controlled conditions in the greenhouse at 25 ± 2 0C and 70 ± 5% RH. Each plant was grown in a 15-cm-diameter plastic pot in a mixture of loam, sand, peat, and fertilizer. The pots were watered on alternate days. The soil was fertilized every two weeks with a standard dilution of fertilizer 15-30-15 (NPK). Five apterous adult melon aphids were transferred from the stock colonies (maintained on each cucumber variety for at least two generations) to one seedling and were allowed to reproduce for 6 hr. The adult aphids and all but one newborn nymph were then removed. Each seedling with one newborn nymph was placed in a pot (9 cm × 6 cm). The pots were placed at 25 ± 1 0C, 60-80 % RH, and photoperiod of 14:10 (L:D) h. The seedlings were replaced every 3 d. Individual nymphs were observed daily for molting and survival. The presence of exuviae was used to determine molting. After the immatures became adult, they were observed daily for reproduction and survival, and all newborn nymphs were removed. Observations continued until all of the aphids were dead. Development times for each nymphal instar, duration of adult pre-reproductive, reproductive, and postreproductive periods, lifetime fecundity, and average daily reproduction were calculated for each aphid. Thirty aphids were tested for each cucumber variety, but only those individuals that completed development to the adult stage were included in nymphal development time calculations, and individual adults that escaped or were damaged during transfer were excluded from reproduction and survival rate analyses. Data analysis and statistics. Effects of host plant on population growth of melon aphid were assessed by constructing a life table, using age-specific survival rates (Lx) and fecundity (mx) for each age interval (x) per day (Andrewartha and Birch 1954). Growth reproductive rate (GRR) =∑ Lxmx, the number of times a population will multiply per generation, was measured in offspring/aphid/generation. Intrinsic rate of increase (rm) describes the growth potential of a population under a given set of environmental condition and was calculated by iteratively solving the equation ∑e-rmx Lxmx =1. Finite capacity for increase (λ) = erm, the number of times the population will multiply itself per unit of time, was measured in offspring/aphid/d). Mean generation time (T) = ln R0/rm, the mean time required for a given population to finish one generation, was measured in days. Doubling time (DT) (days) = ln 2/rm, the time required for a given population to double its numbers, was measured in days. Data on nymphal development times, adult life spans, fecundity, and daily reproduction for seven cucumber variety-treatment cohorts were analyzed by analysis of variance (ANOVA) and treatment differences were determined by t-test. Results and Discussion Total development time of nymphs showed significant differences within the group of cucumber varieties tested, although the differences for each instar were not always significant. Nymphal development on Tamra 761, Rawa- F1- RS, and F1- hybrid Beit alpha MR was ≈ 1 d shorter compared with that on Hezera 480 and Beth alpha MR. Pre-reproductive period and postreproductive periods of adults were not significantly different among the seven cucumber varieties. However, total adult longevity varied significantly between cucumber varieties, and the aphids reared on Rawa-F1- RS had the longest adult longevity. Both daily reproduction and total fecundity of A. gossypii were significantly different among the tested cucumber varieties, and were highest on Rawa-F1- RS followed by F1- hybrid Beit alpha MR, Beit alpha MR, Hezera 480, Tamra 761, Beth alpha MR, and Beth alpha MR hybrid (Table 1). Cucumber varieties influenced melon aphid population growth parameters (Table 2). Overall population growth rates of melon aphid were highest on Rawa-F1- RS followed by Beit alpha MR, F1- hybrid Beit alpha MR, Beth alpha MR, Beth alpha MR hybrid, Hezera 480, and Tamra 761. The net reproductive rate (R0) on Rawa-F1-Rs was 18 %, 25 %, 38 %, 10 %, 35 %, and 47 % higher and population doubling time (DT) was 7 %, 25 %, 15 %, 15 %, 10 %, and 11 % shorter than these of Beit alpha MR, F1- hybrid Beit alpha MR, Beth alpha MR, Beth alpha MR hybrid, Hezera 480, and Tamra 761, respectively. The values of rm increased markedly more on all the tested varieties than on Beth alpha MR (Table 2). The intrinsic rate of increase (rm) was used in a comparative manner to estimate the degree of fitness of various genotypes to their environment (Ayaia, 1968; Birch et al., 1963; Ohba, 1987). When the values of intrinsic rate of increase (rm) were converted into finite rate of increase (λ) it was clear that the population of A. gossypii had the capacity to multiply about 1.32, 1.27, 1.29, 1.29, 1.34, 1.31, and 1.31 per day on tested varieties (Table 2). This finding indicated that a population of 10 females of A. gossypii could increase in a week to become 69, 53, 59, 59, 77, 66, and 66 individuals (Table 2). Cucumber varieties had a significant effect on melon aphid development and reproduction. RawaF1- RS, Beit alpha MR and Tamra 761 were more suitable for melon aphid than other cucumber varieties with respect to development time, adult longevity, reproduction, and population growth. From the obtained results it could be concluded that the length of the pre-reproductive period of aphids and their reduced fecundity may be attributed to the presence of antibiosis in Beth alpha F1 variety (Table 2). Similar results on the turnip aphid have been reported (Kennedy and AbouGhadir 1979). They stated that the population of the turnip aphid Lipaphis erysimi (Kaltenbach) reared on PTWG (susceptible turnip cultivar) was three times larger than that on ‘Shogoin’ (resistant turnip cultivar). The greenhouse studies indicated that this difference was due primarily to reduced reproduction by turnip aphid on ‘Shogoin’, although a significantly longer prereproduction period on the resistant variety also was involved. The presence of cucurbitacins has been associated with the toxic effect of cucumber leaves, which proved that cucurbitacins evolved in wild cucurbits as a mechanism to protect them from generalized herbivores such as Tetranychus urticae (Koch) (Andeweg and De Bruyin, 1959; Da Costa and Jones, 1971b). Table 1: Average development and reproduction of A. gossypii on seven cucumber varieties under greenhouse conditions. Beit alpha MR Nymph 1st instar 2nd instar 3rd instar 4th instar Total Adult Pre-reproductive period Reproductive period Post-Reproductive period Longevity F1- hybrid Beit alpha MR Beth alpha MR Beth alpha MR hybrid Rawa F1-Rs Hezera 480 Tamra 761 Development time (days ± SE)* 1.7 ± 0.6a 1.5 ± 0.6a 1.4 ± 0.6a 1.5 ± 0.7a 5.9 ± 1.2ab 1.7 ± 0.6a 1.5 ± 0.6a 1.2 ± 0.6c 1.1 ± 0.6b 5.4 ±0.9a 1.6 ± 0.6a 1.7 ± 0.6ab 1.6 ± 0.7a 1.2 ± 0.4b 6.0 ± 1.0b 1.5 ± 0.6ab 1.4 ± 0.6a 1.6 ± 0.6a 1.3 ± 0.6b 5.8 ± 0.9ab 1.4 ± 0.6b 1.3 ± 0.5a 1.4 ± 0.6a 1.3 ± 0.4b 5.4 ± 0.9a 1.6 ± 0.6a 1.8 ± 0.6b 1.8 ± 0.6b 1.6 ± 0.6a 6.1 ± 1.2ab 1.2 ± 0.4c 1.4 ± 0.4a 1.0 ± 0.4c 1.3 ± 0.4b 5.2 ± 0.9a 1.1 ± 0.7a 16.4 ± 0.9a 0.9 ± 0.1a 18.4 ± 0.1a 1.6 ± 0.6b 15.8 ± 0.1a 1.0 ± 0.8a 18.4 ± 0.1b 1.2 ± 0.1a 9.9 ± 0.8b 1.0 ± 0.8a 12.1 ± 0.1c 0.9 ± 0.1a 16.2 ± 0.1a 1.0 ± 0.1a 18.1 ± 0.1a 0.7 ± 0.6a 15.6 ± 0.8a 0.8 ± 0.1a 17.1 ± 0.1a 0.7 ± 0.6a 14.5 ± 0.1a 0.9 ± 0.1a 16.1 ± 0.9ab 0.8 ± 0.1a 15.2 ± 0.1a 1.0 ± 0.1a 17.0 ± 0.1ab 40.6 ± 2.6b 3.3 ± 0.1b 40.2 ± 3.1b 2.6 ± 0.1a Reproduction (offspring/female ± SE)* Total fecundity Daily reproduction 52.5 ± 2.4a 3.2 ± 0.1a 47.4 ± 2.1a 3.0 ± 0.1a 42.5 ± 2.9b 3.6 ± 0.1a 50.5 ± 3.2c 3.4 ± 0.1a 59.3 ± 2.8b 3.8 ± 0.1b * Mean within a row sharing the same letter are not significantly different (α = 0.05, t-test). Table 2: Life table parameters of A. gossypii reared on seven cucumber varieties under greenhouse conditions. Varieties Parameters Growth reproduction rate (GRR) Net reproductive rate (R0) Generation time (T) Doubling time (DT) Intrinsic rate of increase (rm) Finite capacity for increase (λ) Population increase of 10 females in 1 week Beit alpha MR F1- hybrid Beit alpha Beth alpha MR Beth alpha MR hybrid Rawa F1-Rs Hezera 480 Tamra 761 52.5 42.6 13.4 2.48 0.28 1.32 69 47.4 40.2 15.4 2.89 0.24 1.27 53 42.5 36.5 13.8 2.67 0.26 1.29 59 50.5 45.6 14.7 2.67 0.26 1.29 59 59.3 50.4 13.06 2.31 0.30 1.34 77 40.6 37.3 13.4 2.56 0.27 1.31 66 40.2 34.2 13.08 2.57 0.27 1.31 66 Hafiz- cucurbits- oral- Entomology- GFC. Literature Cited Andeweg, J.N., and J.W. De Bruyin. 1959. Breeding for non-bitter cucumbers. Euphytica 8:1320. Andrewartha, H.G., and L. G. Birch. 1954. The distribution and abundance of animals. University of Chicago Press. Chicago, Illinois. Ayaia, F.J. 1968. 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