Lifetime egg maturation by host-deprived Venturia canescens

The study investigated egg maturation and deposition by the endoparasitoid wasp Venturia canescens under conditions of host deprivation. Female V canescens maintained without hosts began to deposit eggs onto the sides of the culture vessel on the day of eclosion. The maturation of additional eggs was not inhibited once the maximum oviduct egg load was reached but rather continued for the duration of the experiment (up to 39 days), at a rate of around 5.8% of the remaining unmatured eggs per day. Following host access, wasps matured additional eggs at an increased rate. Artificial damage to the ovipositor resulted in a reduced rate of egg maturation even though the oviducts were partly egg depleted, while damage to the auxiliary valvulae had no effect. These results suggest two conclusions. Under conditions of host deprivation, the rate at which eggs are matured is determined by the rate of synthesis of precursors by the fat body that in turn is modified by feedback from the ovipositor, induced by physical stimulation. Further, the discarding of eggs is due to the involuntary unidirectional movement of eggs down the oviduct, facilitated by the ongoing maturation of additional eggs. (C) 2003 Elsevier Ltd. All rights reserved.