Biology and control of the fruit borer, Conopomorpha sinensis Bradley on litchi (Litchi chinensis Sonn.) in northern Thailand

Fruit and leaf shoot of litchi (Litchi chinensis) infestation by naturally occurring populations of the fruit borer, Conopomorpha sinensis larvae and C. sinensis parasitization rates were determined in litchi orchards in northern Thailand at high (ca. 1 400 m ASL) and low (ca. 800 m ASL) elevations with different, non-over-lapping fruiting seasons. In addition, spray applications of Bacillus thuringiensis var. aizawai, the natural compound spinosad and the chemical pesticide imidacloprid were conducted in the field to test the effects of these agents on C. sinensis fruit infestation rate. Fruit infestation rate and fruit growth, studied in a low elevation orchard, were sigmoidal and showed a highly significant positive correlation (P· 0.01). Leaf shoot infestation rate in the low elevation orchard decreased in the course of the fruiting season (March until May), but increased in the high elevation orchard, where no fruits were present within the same period of time. Together, these results indicate that females of C. sinensis clearly prefer fruits over shoots for oviposition. If no fruits are available, which was the case in the high elevation orchard during that time, they are constrained to lay their eggs on shoots. The parasitization rate of C. sinensis larvae in untreated fruits was 54.3%. The parasitoid species were Chelonus chailini (90.8%) and Phanerotoma sp. (9.2%). In the leaf shoots, C. sinensis was found to be parasitized by Phanerotoma sp. and Apanteles briareus. The applications of the different active agents had no significant effect on C. sinensis fruit infestation compared to the untreated control. Besides the cryptic life of the larvae, this is most probably explained by the fact that C. sinensis has several generations during the fruiting season. Because of the high parasitization rates recorded, an alternative and more effective control measure than the application of pesticides might be the augmentative release of parasitoids.