Abstract
Body size is a standard criterion of quality control in insect rearing and often assumed to correlate with fitness in parasi- toid wasps, but various metrics of body size can be used. The purpose of this study was to determine which morphological feature provides the best correlation with body size and egg load in a thelytokous population of the parasitoid wasp, Lysiphlebus fabarum (Marshall), when reared on Aphis fabae Scopoli under standardized conditions in a growth chamber (21 ± 1°C, 60-70% RH, and 16L : 8D). Candidate metrics included head width, length and width of the pronotum, length and width of the right forewing, and length of the right hind tibia. In the first experiment, correlations were determined between these measurements and overall wasp body length. As head width and hind tibia length emerged as the most suitable proxies for total body length, the next experiment these two variables as proxies for egg load in females reared from different nymphal instars of the host aphid. There was a non-linear relationship between body size and egg load of wasps emerging from hosts parasitized in different nymphal instars. Egg load increased linearly with body size across all host growth stages, but the second nymphal instar was the most suitable stage for para- sitism when speed of development was factored in. The results suggest that head width is a suitable morphometric for monitoring quality control in mass-reared cultures of this wasp.
Highlights
Lack of quality control procedures during the mass production of natural enemies may lead to failures in biological pest control (Calkins & Ashley, 1989)
Parasitoid size is determined by the total amount of nutritional resources available during larval development (Jervis et al, 2008). These nutritional resources vary as a function of host quality, which in turn depends on species (Harvey & Vet, 1997; Sampaio et al, 2008), age or growth stage (Sequeira & Mackauer, 1992a, b) and environmental conditions (Li & Mills, 2004; Xu et al, 2008)
This paper reports the results of experiments that were designed to assess the relative utility of various morphological measurements as predictors of body size and egg load, as well as the relative suitability of different host growth stages, in Lysiphlebus fabarum (Marshall) (Hymenoptera: Aphidiinae), a solitary koinobiont parasitoid that commonly parasitizes Aphis fabae Scopoli in Iran (Rakhshani et al, 2006; Talebi et al, 2009)
Summary
Lack of quality control procedures during the mass production of natural enemies may lead to failures in biological pest control (Calkins & Ashley, 1989). Body size is one of the standard elements of quality control (van Lenteren et al, 2003), as it can have important effects on components of parasitoid fitness (i.e. mating success in males and egg load, egg size and longevity in females) (Godfray, 1994). Parasitoid size is determined by the total amount of nutritional resources available during larval development (Jervis et al, 2008). These nutritional resources vary as a function of host quality, which in turn depends on species (Harvey & Vet, 1997; Sampaio et al, 2008), age or growth stage (Sequeira & Mackauer, 1992a, b) and environmental conditions (Li & Mills, 2004; Xu et al, 2008). The best morphological indicators of parasitoid fitness probably vary among species
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