Influence of different densities and nymphal instars of Aphis gossypii (Hemiptera: Aphididae) on developmental time and feeding rate of larvae of Episyrphus balteatus (Diptera: Syrphidae) under greenhouse conditions

Several aphidophagous insects such as predators and parasitoids are known to respond positively to aphid infested plants. This study was intended to evaluate the effect of different densities (40, 60, 80, 100) and nymphal instars (1st, 2nd, 3rd, 4th) of the cotton aphid Aphis gossypii Glover (Hemiptera: Aphididae) as prey on developmental time and feeding rate of the larvae of the syrphid fly Episyrphus balteatus DeGeer on cucumber leaves. The experiment was conducted at the greenhouse condition (22± 5°C, 55± 10% RH and 14L: 10 D h photoperiod) with 10 replications. Our study indicated that lower density and poor quality of prey caused higher larval mortality. Feeding on 3rd and 4th nymphal instars and higher density of prey (80 and 100 prey/day) caused shorter developmental time of E. balteatus. The larvae fed on densities of 40 and 60 prey, even though fed on higher nymphal instars, failed to complete their larval development. It is concluded that higher prey densities (80 and 100 prey) were highly suitable for predator's larval development and significantly reduced the developmental period of E. balteatus. These findings provide further evidence that E. balteatus has high predation capacity on aphids, and therefore can be used as a successful biocontrol agent against A. gossypii.