Biological control (biocontrol) of crop pests is a sustainable alternative to the use of biodiversity and organismal health‐harming chemical pesticides. Aphids can be biologically controlled with parasitoid wasps; however, variable results of parasitoid‐based aphid biocontrol in greenhouses are reported. Aphids may display genetically encoded (endogenous) defences that increase aphid resistance against parasitoids as under high parasitoid pressure there will be selection for parasitoid‐resistant aphids, potentially affecting the success of parasitoid‐based aphid biocontrol in greenhouses. Additionally, aphids may carry secondary bacterial endosymbionts that protect them against parasitoids. We studied whether there is variation in either of these heritable elements in aphids in greenhouses of sweet pepper, an agro‐economically important crop in the Netherlands that is prone to aphid pests and where pest management heavily relies on biocontrol. We sampled aphid populations in organic (biocontrol only) and conventional (biocontrol and pesticides) sweet pepper greenhouses in the Netherlands during the 2019 crop growth season. We assessed the aphid microbiome through both diagnostic PCR and 16S rRNA sequencing and did not detect any secondary endosymbionts in the two most encountered aphid species, Myzus persicae and Aulacorthum solani. We also compared multiple aphid lines collected from different greenhouses for variation in levels of endogenous‐based resistance against the parasitoids commonly used as biocontrol agents. We found no differences in the levels of endogenous‐based resistance between different aphid lines. This study does not support the hypothesis that protective endosymbionts or the presence of endogenous resistant aphid lines affects the success of parasitoid‐based biocontrol of aphids in Dutch greenhouses. Future investigations will need to address what is causing the variable successes of aphid biocontrol and what (biological and management‐related) lessons can be learned for aphid control in other crops, and biocontrol in general.

Anthropogenic global warming and attendant effects like heatwaves affect the biology and ecology of both individuals and species within and across different trophic levels. Here, we examined the effects of a simulated heatwave on development of and competition between two hyperparasitoid wasps, Lysibia nana and Acrolyta nens when attacking the same host, cocoons of the primary parasitoid, Cotesia glomerata. Parasitized hosts were exposed to three different day and night temperature regimes (low, medium and high) that reflect cool, normal and heatwave conditions in the Netherlands. We found that higher temperatures decreased survival to eclosion more strongly in the hyperparasitoids than in their host. Heatwave conditions also shortened development time and led to the production of smaller adult wasps of both hyperparasitoid species in singly parasitized hosts. In multiparasitized hosts, L. nana won most of the contests when it oviposited first, irrespective of the time interval between the first and second parasitism, whereas A. nens only dominated when it had a 24 h head start or longer. Most importantly, our results show that L. nana in particular benefited in competition at higher temperatures, perhaps due to an increase in the metabolic rate and more rapid egg and/or larval development. This may potentially reduce opportunities for coexistence following heat waves. Our results suggest that heatwaves associated with global warming will enhance the rate of development, but negatively affect survival and other fitness‐related traits in (hyper)parasitoids. Moreover, the outcome of larval competition may be determined via physiological responses that are species‐specific and thus influence phenology.

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