Facilitated harvesting of eggs from laboratory-reared Chrysoperla externa (Neuroptera: Chrysopidae)

Abstract

Chrysoperla externa (Neuroptera: Chrysopidae) eggs are attached to the oviposition substrate by long silk stalks. The complete removal of these stalks is crucial for efficient egg release in biological control programs. The present study aimed at establishing an appropriate oviposition substrate and determining the best embryonic stage for submission of C. externa eggs to manual destalking and harvesting. Eggs oviposited on bond or chamois paper substrates were transferred from rearing cages and incubated in a growth chamber under controlled conditions for 24, 48, 72 or 96 hours according to the embryonic stage development required. Substrates were positioned in an inclined tray and softly brushed with a folded rectangle of soft muslin cloth. Destalked eggs were placed individually in microtiter plates and incubated in a growth chamber until hatching. Egg destruction at all embryonic stages and oviposition on the chamois substrate were considerably higher as compared to those from bond paper. Young eggs harvested from chamois paper were particularly susceptible and exhibited 88 % destruction, whereas eggs aged 48, 72 or 96 hours showed < 10 % destruction on both substrates. Viability of eggs collected at 24 hours for both substrates was significantly different from the observed for the other embryonic stages. The method described will contribute to improve the efficiency of manual harvesting of C. externa eggs and can be employed as an alternative to chemical techniques of destalking in mass rearing.