Responses of Parasitoids (Hymenoptera) of Diaspis boisduvalii (Hemiptera: Diaspididae) to Insecticides and Herbicides in Costa Rican banana plantations.

Abstract

Abstract Armored scale insects (Hemiptera: Diaspididae) have been identified as pests worldwide. In Costa Rica, various armored scale insects are economically important in the production of agricultural and horticultural products for exportation. Diaspis boisduvalii Signoret is a primary insect pest in banana plantations, causing substantial economic losses and high control costs. In order to determine the effect of insecticide and herbicide use on percent parasitism of D. boisduvalii on banana (Musa AAA “Cavendish”) in Costa Rica, six commercial plantations with varying insecticide and herbicide use were sampled over a five-month period. Pseudopetioles from the oldest pseudoleaf of banana plants infested with scale insects were collected monthly at each site. Each pseudopetiole fragment (55 cm2) was stored in a well-ventilated glass tube and monitored daily for parasitoid emergence, percent parasitism, and sex ratio. Four parasitoid species from two families were identified. A gregarious ectoparasitoid Aphytis sp., a solitary endoparasitoid Coccobius sp. and a very rare hyperparasitoid Ablerus sp. (Aphelinidae), and a solitary endoparasitoid Plagiomerus peruviensis (Girault) (Encyrtidae). The study revealed a significant negative impact of insecticides (p < .001), but species-specific responses to herbicides. Rather suprisingly, P. peruviensis showed a higher percent parasitism in plantations with herbicides than without herbicides, unlike the other parasitoids. Results from sex ratios suggest that P. peruviensis reproduces via thelytokous parthenogenesis.