Abstract
Several studies have demonstrated that the invasive ladybird Harmonia axyridis is a strong intra-guild predator of native species of ladybird. Laboratory studies have shown that H. axyridis can be an intra-guild predator of aphid predators other than coccinellids, including the hoverfly Episyrphus balteatus and lacewing Chrysoperla carnea. However, little is known about the effect of intra-guild predation (IGP) by H. axyridis on hoverfly and lacewing populations in the field. In the present study molecular analyses were used to detect the DNA of E. balteatus and C. carnea in the gut contents of H. axyridis. Primers for the syrphid and chrysopid prey were designed and feeding experiments performed to determine how long prey DNA remains detectable in the guts of this ladybird. DNA detection was influenced by the life stage of the predator and species of prey. Meal size did not affect detection time, except when fourth instar individuals of H. axyridis were fed 10 eggs or one second instar of C. carnea. Predator weight, sex and morpho-type (melanic/non-melanic) did not influence DNA detection. The half-life of the time for which the DNA of the prey remained detectable was calculated for each predator-prey combination, and ranged from 8.9 to 52.4 h. This method can be used to study the ecological importance of IGP by H. axyridis on aphidophagous predators other than coccinellids in the field.
Highlights
Intra-guild predation (IGP) is a widespread phenomenon, which occurs when one predator consumes another that is competing for the same prey
Except for Platycheirus peltatus Meigen, the bands for the other hoverflies were of similar size and intensity as that for E. balteatus (Fig. 1)
The primers for C. carnea fulfilled these requirements, those for E. balteatus were not entirely species-specific, as they amplified DNA of a few other species of hoverfly. These primers may still be useful for assessing the incidence of intra-guild predation (IGP) in the field under certain circumstances, for example, if E. balteatus outnumbers other hoverfly species at the investigated site
Summary
Intra-guild predation (IGP) is a widespread phenomenon, which occurs when one predator consumes another that is competing for the same prey. It differs from classical predation because it reduces the incidence of scramble competition (Polis et al, 1989). IGP occurs in a variety of ecosystems at different trophic levels It affects the distribution, abundance and evolution of the intraguild predator, intra-guild prey and their common prey (Polis et al, 1989; Arim & Marquet, 2004). In the UK, Belgium and Switzerland, invasion by H. axyridis is associated with the decline in the abundance of several native species of ladybird (Brown et al, 2011a; Roy et al, 2012), ostensibly due to direct competition and IGP
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