Use of gamma radiation for improving the mass production of Trichogramma chilonis and Chrysoperla carnea

Abstract

Gamma radiation studies were conducted to improve the existing mass rearing capabilities for an egg parasitoid, Trichogramma chilonis Ishii and a predator, Chrysoperla carnea Stephens as part of a program to achieve an area-wide control of cotton and sugarcane pests. The suitability of host (Sitotroga cerealella Olivier) eggs for parasitization by T. chilonis was restored and prolonged from 3 to 7 days pre-hatching with the application of gamma radiation in the range of 5–55 Gy. The findings indicated that all treatment doses were effective but varied significantly in parasitization of eggs. This effect was similar during the first 2 days ranging from 78 to 94% parasitization, but it decreased drastically at lower doses (5 and 15 Gy) in succeeding days. High doses were better than low doses. For the highest treatment dose (55 Gy), successful parasitization declined only gradually, resulting in 45% parasitization even after 7 days. This finding would allow for reliable supply of viable host eggs to small insectaries in remote areas. Studies on C. carnea showed that feeding of irradiated prey eggs increased larval survival, fecundity and female sex ratio. Larval survival improved by 89% over the control when C. carnea was fed eggs irradiated with a dose of 45 Gy. The effects of radiation-treated prey eggs on survival and fecundity of C. carnea persisted in successive generations, but were considerably less in the F2 than in the F1 and P generations. At 45 Gy, fecundity was highest with 444 eggs/female in the parent, 397 in F1, and 311 in F2 generations, whereas it decreased significantly at lower doses and in untreated eggs.