Studies on the biology of Encarsia pergandiella Howard, a solitary, arrhenotokous endoparasite, revealed that fertilized eggs, which give rise to females, are deposited in whitefly nymphs preferably in second, third or fourth instar, while unfertilized eggs, which give rise to males, are deposited in Encarsia larvae at whose expense they develop. The parasite adults were observed to feed on body fluids of whitefly nymphs. Both sexes have a pupal and three larval stages, and development from egg to adult at approximately 75° F. takes 15 days for the females and 13 to 14 days for the males. Mean longevity of the females at constant and fluctuating temperatures was studied. Actual mean fecundity at 75 ± 4° F. was 48.5 eggs per female, all of which were deposited during the first 70% of her life, provided hosts were abundant. Field observations revealed that E. pergandiella was present throughout the year, reaching highest numbers in the spring and summer. The parasite does not have an obligatory period of dormancy for all of its individuals. E. pergandiella was not able to prevent whiteflies from causing heavy damage to plants. The reason may be in the discrepancy between the rate of increase of the whitefly and the parasite.
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