Keep an eye on natural enemies: What Aphidius on sticky traps tells us about aphid pest population dynamics

Abstract

Monitoring pest population development in crops is crucial for determining action thresholds and evaluating the efficacy of pest control measures in greenhouse integrated pest management. Yellow sticky traps are a popular choice for trapping various pests; however, they may not be effective in capturing wingless or immature pests. For instance, winged aphids can only be trapped during their dispersal activities; thus, relying solely on sticky traps for monitoring can be insufficient and may result in an inaccurate estimation of population density. Therefore, we investigated a new approach for the indirect monitoring of the cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), on cucumbers, Cucumis sativus L. (Cucurbitaceae) by monitoring the natural enemies on sticky traps. The study aimed to assess aphid population density in crops via the foraging activities of Aphidius colemani Viereck (Hymenoptera: Braconidae). In theory, the patch time allocation of parasitoids should increase with increasing host density, whereas the probability of trapping parasitoids on sticky traps should decrease. To test this hypothesis, we infested cucumber crops in greenhouse cabins with different aphid densities and hung yellow sticky traps before releasing A. colemani. Insects were counted weekly on the plants and sticky traps, and their relationships were analyzed using correlation modeling. The trap catches strongly correlated with aphid population density in the crops, but this correlation was positive, contrary to our expectations. Nevertheless, in the absence of winged aphids, indirect assessments could be a valuable tool for monitoring pest populations. Furthermore, our study confirms that monitoring winged aphids on yellow sticky traps is not a reliable method for the surveillance of the actual aphid population density in the crops. The possibilities of the biological control and monitoring of non‐flying insects are discussed.