Modelling movement and stage-specific habitat preferences of a polyphagous insect pest

Abstract

Background: The feeding preferences of Diabrotica speciosa (Coleoptera: Chrysomelidae) cause a parent-offspring conflict, as providing the best host for the offspring development is detrimental to adult survival and fecundity. Understanding the implications of this conflict could help entomologists to implement pest-management programs. With this in mind, the foraging behaviour of D. speciosa was investigated using an individual-based model in two distinct scenarios. Methods: In an intercropping scenario, parent-offspring conflict was simulated when adult insects exploit two crops (corn and soybean) that provide different nutritional advantages for each insect stage. First, we compared three hypothetical types of adult dispersal, considering a continuous oviposition over time: Diffusion, attracted to a fixed host and alternating the preference between hosts with frequency 1 τ 1/4 1τ, where τ is the time in days spent foraging for each host. We also simulated two principles: "mother knows best" (adult females foraging for corn during the oviposition period) and "optimal bad motherhood" (adult females remain foraging for soybean to maximise their own fitness during the oviposition period), but considering the existence of a pre-oviposition period. In a landscape scenario, we investigated the population dynamics in an area composed by 4 crop plots that change over time. Results: Among dispersal types considering continuous oviposition, the crop-alternating movement a-3 performed best, when close to an optimal τ. Additionally, τ was predicted to be influenced mainly by the width of crop rows. We also verified that the "mother knows best" strategy is better for the population growth than the "optimal bad motherhood". In the landscape scenario, we observed that including fallow periods in the crop calendar and adopting a more-heterogeneous arrangement of crop plots reduced the density of this insect. Conclusion: Both the continuous and sequential oviposition simulations indicate that foraging involving switching of target crop benefits population fitness. In the landscape scenario, arranging crop plots more heterogeneously and avoiding vast areas of soybean can help farmers to control this insect pest. Additionally, fallow periods can also reduce significantly D. speciosa populations.