Bulletin of Insectology (2017) 70, 49-55

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Luca Picciau, Chiara Ferracini and Alberto Alma (2017)
Reproductive traits in Torymus sinensis, biocontrol agent of the Asian chestnut gall wasp: implications for biological control success
Bulletin of Insectology 70 (1), 49-55
Abstract: Torymus sinensis Kamijo is the main parasitoid associated with the Asian chestnut gall wasp Dryocosmus kuriphilus Yasumatsu. It was released as biocontrol agent in Asia and many European countries in order to contain the gall wasp outbreaks. It is reported as univoltine, but it also exhibits a prolonged diapause mainly as late instar larva. In the two-year period (2014-2015) we investigated longevity, egg load, ovigeny strategy, and body metrics of T. sinensis under laboratory conditions in order to assess the potential fecundity and the effects of age on the egg load, considering univoltine and diapausing adult wasps. T. sinensis females reached a maximum age of 102 days as univoltine and 73 days as diapausing adults. Newly emerged adult wasps contained 0.5 ± 0.31 and 0.9 ± 0.60 mature eggs in the univoltine and diapausing population, respectively. The total mean egg load (mature + immature oocytes) recorded for the univoltine females at day 0 was 215 ± 2.43 whilst for the diapausing females was 240 ± 2.31. The ovigeny index calculated for univoltine wasps was 0.0023 and 0.0041 for diapausing ones, indicating for both populations an extremely synovigenic behaviour. Except for the first two weeks, diapausing females had a higher egg load that univoltine. Univoltine males, females and their eggs showed to be significantly larger than diapausing ones. A decrease in egg load with an increase in adult female age was found in both populations, probably due to egg resorption. This study demonstrates that the aging of parasitoids plays an important role concerning the egg load, influencing the effectiveness of T. sinensis in the context of biological control programs, and suggesting that 2-3 week-old females have to be preferred during the release stage in order to maximize parasitism. Implications of these reproductive traits for the success of T. sinensis as biological control agents are discussed.
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Database assignments for author(s): Alberto Alma

Research topic(s) for pests/diseases/weeds:
biocontrol - natural enemies
Research topic(s) for beneficials or antagonists:
general biology - morphology - evolution

Pest and/or beneficial records:

Beneficial Pest/Disease/Weed Crop/Product Country Quarant.

Dryocosmus kuriphilus Chestnut (Castanea) Italy
Torymus sinensis (parasitoid) Dryocosmus kuriphilus Chestnut (Castanea) Italy