Effect of Some Cucumber Cultivars on Biological and Population Growth Parameters of Aphis gossypii (Glover) and Functional Response of Chrysoperla carnea (Stephens)

The melon aphid, Aphis gossypii Glover is a polyphagous pest that causes serious damage to various crops including vegetables. This insect is one of the most important pests of cucumber plant in greenhouses throughout the world. Biological control is one of the alternative or complementary methods for chemical control that can be used in IPM programs. The use of natural enemies can be very effective in reducing the population of invasive pests. Among biological control agents, Chrysoperla carnea (Stepehns) has attracted the most attention as an effective pest control agent. Also, using resistant cultivars is one of the important methods for pest control management. Therefore, the use of resistant cultivars with effective biological control agents plays an important role in pest control. The aim of this study was to investigate the effect of some cucumber cultivars on biological and population growth parameters of A. gossypii and the functional response of C. carnea.

Four cucumber cultivars including Arshia, Caspian, Danito and Tarom were used in this study. Life table experiments were performed using 50 first instar nymphs (< 24 h old) for each cucumber cultivar. The nymphs were separately reared on the leaves of each cultivar. After emergence of adults, their fecundity and survival were recorded daily until all of them were dead. The parameters were estimated using TWOSEX-MS Chart, life table procedure. In the functional response experiment, different densities (2, 4, 8, 16, 32, 64 and 128) of 3- and 4-d- old aphid nymphs were separately offered to the third instar larvae of C. carnea, which were starved for 16 h before the test. The number of consumed preys was recorded after 24 h. The experiment was repeated 10 times for each aphid density and cucumber cultivar. Logistic regression analysis and nonlinear least square regression procedure were used to determine the type of functional response and estimate the parameters, respectively. The experiments were carried out in a greenhouse at 25±2 °C, 65±5% RH and a photoperiod of 16:8 (L: D) h.

Based on the results, the highest values of intrinsic rate of increase (rm) and net reproductive rate (R0) of the aphid were estimated on Tarom (0.443 ± 0.009 and 30.14 ± 2.05, resp.) and the lowest values were on Caspian (0.297 ± 0.009 and 16.78 ± 1.55, resp.) and Danito (0.305 ± 0.011 d-1 and 16.62 ± 1.60 per generation, respectively). The finite rate of increase (λ) ranged from 1.346 ± 0.013 on Caspian to 1.557 ± 0.015 d-1 on Tarom. The lowest values for mean generation time (T) and doubling time (DT) of the aphid were estimated on Arshia and Tarom cultivars. In the second experiment, the predator exhibited functional response type III on all cucumber cultivars. The attack constant (b) for the third instar C. carnea varied from 0.00121 to 0.00168 and its handling time (Th) ranged from 0.3145 to 0.4596 h on different cucumber cultivars.

Comparison of the biological parameters showed that Tarom cultivar with the highest values of rm and λ is a relatively desirable cultivar for the growth and feeding of A. gossypii. In contrast, Caspian cultivar is less desirable for A. gossypii. Also, according to the parameters of attack constant (b) and handling time (Th), it seems that Caspian and Danito are more suitable cultivars for biological control of A. gossypii than other two cultivars. However, additional studies under greenhouse conditions are needed to provide further details of different cucumber cultivars, A. gossypii and C. carnea.