Effect of different feeding sources on lifespan and fecundity in the biocontrol agent Torymus sinensis

Abstract

Torymus sinensis Kamijo (Hymenoptera, Torymidae) is a biocontrol agent released to control outbreaks of the Asian chestnut gall wasp, Dryocosmus kuriphilus Yasumatsu (Hymenoptera, Cynipidae). This wasp is mass reared in controlled conditions in order to be released on a large scale in chestnut orchards and coppices, thus factors such as food quality may deeply influence the effectiveness of parasitoids. To identify different diets that could be used to increase mass rearing, performance, longevity and fecundity of T. sinensis were assessed using honey (diet 1), honey plus pollen (diet 2), pollen (diet 3), and water (diet 4), compared to unfed wasps (control) in laboratory experiments.In the present study diet quality greatly influenced survival and reproductive output in T. sinensis. Adults using honey plus pollen as food had the longest life span, and significantly increased fecundity compared to pollen alone, water, and unfed wasps. Median lifespan (day at which 50% of the initial number of wasps are still alive) was 31, 31, 2.5, 4, 1.5 days, in the honey, honey plus pollen, pollen, water, control, respectively.The egg production in wasps fed with honey and honey plus pollen observed over lifetime showed that the newly emerged specimens had an average of 2.40 ± 0.21 and 0.14 ± 0.12, respectively at day 0. The number of mature eggs increased rapidly reaching in diet 1 the highest average number, 26.60 ± 2.48, at day 6, and 30.2 ± 1.59 at day 7 in diet 2. No significant difference in the mean number of mature eggs between diets 1 and 2 was observed during all 13 weeks except for week 11. The mean number of reabsorbed eggs was 0 both in diet 1 and 2 at day 0. The mean number increased till 2.80 ± 0.66 at day 10 and 1.40 ± 0.24 at day 14 in diet 1 and 2, respectively.The cumulative lifetime mean egg load was 1012.67 and 1095.82 for honey and honey plus pollen, respectively, which was significantly higher than 32.40 for pollen, 58.40 for water and 43.57 for control.Based on our studies, feeding the female wasps with honey and pollen increased lifespan by 33-fold, and fecundity by 2.3-fold at day 4 over unfed wasps.This work contributes to a better understanding of the influence of different diets on lifespan and fecundity in the parasitoid wasp T. sinensis, to the refinement of mass rearing in controlled conditions, and to the optimization of classical biocontrol programs. Prior to the field release, it seems advisable to supply insects with sugar-rich diets to improve their performance in fields and to enhance parasitoid egg expenditure.