The effects of periodic warming on the survival and fecundity ofDiadromus pulchellusduring long-term storage

Abstract

Biological control strategies capitalise on natural mechanisms such as predation and parasitism to reduce the need for chemical applications to control insect pests. In Canada, the parasitic wasp Diadromus pulchellus Wesmael (Hymenoptera: Ichneumonidae) is being investigated for its use in the biological control of an invasive crop pest, the leek moth, Acrolepiopsis assectella (Zeller) (Lepidoptera: Acrolepiidae). Large numbers of insects will be needed for releases to ensure that populations of D. pulchellus establish quickly and impact leek moth populations. Since the current culture is not producing the number of insects required for largescale releases, the accumulation and storage of D. pulchellus might be a viable option to obtain ideal numbers. Currently, little is known about the optimal conditions for the long-term storage and release of D. pulchellus, which overwinter in nature as adults. Using insects from the active culture, the effect of intermittent, short-term warming on cold-stored adults was evaluated for survivorship and fecundity. In accordance with previous findings, females survived cold storage more readily than males. However, the warming regimes employed had no significant impacts on overall survivorship. Cold-stored females had reduced fecundity compared to females maintained in the culture, though no significant differences were noted between the treatments. In addition, the offspring sex-ratio for all treatments was male skewed. Thus, the warming procedures utilised provided no advantages over current techniques for the long-term storage of D. pulchellus intended for release.

Mechanisms underpinning the beneficial effects of fluctuating thermal regimes in insect cold tolerance

“…In another case, FTR slightly reduced adult longevity (Ismail et al, 2013), which could reduce lifetime fecundity if that species continues to reproduce throughout the adult stage. However, in another study using Diadromus pulchellus, there was no effect of FTR on the number of mated females or fecundity compared with CLT (Murdoch et al, 2013). The rationale for the existence of a fitness cost is that, during recurrent warm periods of FTR, the overshoot in metabolic rate (Lalouette et al, 2011;Yocum et al, 2011;Boardman et al, 2013) may progressively consume more energy stores than under CLT.…”

Effects of fluctuating thermal regimes on cold survival and life history traits of the spotted wing Drosophila (Drosophila suzukii)

“…Ismail et al (2010) did not observe any fecundity decrease after FTR exposition in Aphidius ervi females. Likewise, Murdoch et al (2013) tested the effect of warming interruptions applied once or thrice during a cold storage period of 8-week and found no differences between constant or fluctuating storage on fecundity of the leek moth Diadromus pulchellus. Allocation of limited energy often results in life-history trade-offs, for instance between reproduction and longevity (Zera & Harshman, 2001;Attisano et al, 2012).…”

Effects of Temperature and Wildflower Strips on Survival and Macronutrient Stores of the Alfalfa Leafcutting Bee (Hymenoptera: Megachilidae) Under Extended Cold Storage

“…Compared to STR, FTR has been associated with lower lipid content, body mass, fecundity, and longevity of some insects ( Carroll and Quiring 1993 ; Ismail et al 2010 ; Marshall and Sinclair 2010 ; Basson et al 2012 ). For other insects, no differences in fecundity ( Murdoch et al 2013 ) or flight performance and metabolism ( Bennett et al 2013 ) have been observed. Comparative studies that track macronutrient stores through overwintering may help us better understand the net benefits and costs of FTR and the role nutrition plays in overwintering success.…”