Functional Response of Diaeretiella rapae (Hymenoptera: Braconidae) to Myzus persicae Density on Canola

Abstract

Quantification of host–parasitoid interactions involving Diaeretiella rapae (Hymenoptera: Braconidae) and Myzus persicae on canola (Brassica napus L.) was conducted to determine functional response type and parasitization efficiency across varying aphid densities under controlled laboratory conditions. Third-instar and adult aphids were exposed to a range of initial densities, and parasitism rates, handling time, and attack rates were estimated using nonlinear regression models. Results indicated a density-dependent increase in parasitism up to a saturation threshold, consistent with a Type II functional response, where parasitism rate decelerated at higher host densities due to increased handling time constraints. Estimated parameters revealed high searching efficiency at low aphid densities, demonstrating the parasitoid’s effectiveness in early infestation suppression. However, reduced marginal parasitism at elevated prey densities suggests limitations in outbreak scenarios without complementary control measures. The regression model provided a strong fit to observed data, validating the applicability of Holling’s disc equation for describing this interaction system. Environmental conditions such as temperature and host plant quality influenced parasitoid performance, with improved attack rates observed under optimal canola growth stages. Findings highlight the ecological potential of D. rapae as a biological control agent in integrated pest management programs targeting aphid populations in oilseed crops. Understanding functional response dynamics enhances predictive modeling of biological control outcomes and supports deployment strategies for augmentative releases in field conditions. These results contribute to refining sustainable pest suppression strategies in Brassica agroecosystems under variable infestation pressures. Further field validation under multi-location conditions is recommended to strengthen applicability across diverse agro-climatic regions globally.