Effect of Temperature and Aphid-Host Plant Variety on Performance and Thermal Requirments of Coccinella undecimpunctata L. and Cheilomenes propinqua isis (mulsant)

Abstract

In this study, the single and common effects of temperature (20, 25 and 30 ± 1˚C) and eggplant varieties (Classic, 0111, and Anan) on the developmental performance and heat requirements of Coccinella undecimpunctata L. and Cheilomenes propinqua isis (Mulsant) were examined. The predators were fed upon Aphis gossypii Glover that reared on the three eggplant Solanum melongena (L.) varieties. The two-way ANOVA showed that there was significant effects of temperature and host plant varieties on the total developmental times of both predators. However, the interaction between temperature and host plant variety interaction had only significant effect on the total developmental times of C. undecimpunctata. The results also revealed that the developmental times (DT) of both predators were decreased with increasing the temperature, whereas the developmental rates increased. Based on lower developmental threshold (T0) values, the more tolerant stage for coldness was the pupal stage of both C. undecimpunctata and C. propinqua isis on the three eggplant varieties. On the contrary, the more sensitive stage for low temperature degrees differed for both species: the eggs stage for C. undecimpunctata and the larval stage for C. propinqua isis. The minimum (T0) values for the entire development of both predators were recorded on Classic variety. The heat units (degree-days, DD’s) estimated for each stage showed that aphids produced on Classic variety lowered the amount of heat required by both predator species to complete their development. Further, the larval stage of both predatory species required more heat units to develop at each aphid-host plant variety combination than other stages. These results suggest that eggplant var. Classic has to be considered, in mass rearing programs, to produce a high nutritional prey for both predator species. This might maximize the population of these predators. As well, 30 °C would multiply the population of both predators under the same rearing conditions, and thus has to be generalized.