The solitary pupal parasitoid Diadromus pulchellus was released in 2010 as a classical biological control agent against leek moth, Acrolepiopsis assectella, an important new pest of onion crops, Allium spp. in Eastern North America. Postrelease monitoring using sentinel leek moth pupae revealed that the facultative hyperparasitoid Conura albifrons was attacking leek moth and potentially D. pulchellus as well. We used laboratory choice and no-choice tests to assess the potential impact of C. albifrons on leek moth and D. pulchellus. C. albifrons is capable of developing in newly formed leek moth pupae and leek moth pupae containing first instar D. pulchellus, as well as in fully developed D. pulchellus pupae. Survivorship of both leek moth and D. pulchellus exposed to C. albifrons was significantly lower than that of unexposed controls. In choice trials, prior host experience significantly influenced host choice by C. albifrons. These results suggest that C. albifrons could impact the establishment of D. pulchellus through both competition and intraguild predation, and that the impact has the potential to change as the relative frequency of the two hosts shifts in field populations.
We report successful overwintering of Diadromus pulchellus in North America (Ontario) following introduction of this species from Europe to control the leek moth, Acrolepiopsis assectella, a recently established alien species. Field rearing revealed that the native Diadromus subtilicornis emerged only from diamondback moth, Plutella xylostella, whereas D. pulchellus was reared almost exclusively from leek moth. The single D. pulchellus reared from diamondback moth was anticipated because host range studies found this species could develop on both leek moth and diamondback moth in the laboratory, although, it had not been previously reported from diamondback moth in the field in Europe. DNA barcoding of specimens of both Diadromus spp. confirmed their species status and novel morphological characters are presented to distinguish D. pulchellus from D. subtilicornis. In addition, DNA from specimens of D. subtilicornis from Europe clustered with DNA from specimens across Canada, confirming that it is a single Holarctic species. Finally, a new host association for D. subtilicornis is recorded from the dame's rocket moth: Pseudoplutella porrectella.
Resources added to agroecosystems to enhance biological control are potentially available to multiple members of the resident insect community—not only the biological control agents for which the resources are intended. Many studies have examined the effects of sugar feeding on the efficacy of biological control agents. However, such information is lacking for other, interacting species such as facultative hyperparasitoids, which may contribute to pest suppression but can also interfere with introduced biological control agents. Under greenhouse conditions, we tested the direct effects of sugar and nectar provisioning on the longevity, host‐killing impact and offspring production of two pupal parasitoids associated with leek moth, Acrolepiopsis assectella: the introduced biological control agent, Diadromus pulchellus, and the native facultative hyperparasitoid, Conura albifrons. Adding sucrose, buckwheat or a combination of buckwheat and common vetch to a sugar‐deprived system (potted leek plants in cages) increased parasitoid longevity and resulted in higher leek moth parasitism and mortality compared to water or common vetch treatments. However, the two parasitoid species exhibited a distinct temporal response to the treatments, likely influenced by differences in their life histories. This study provides insight into how integrating conservation biological control techniques could affect the success of a classical biological control programme.
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