Evaluating the effect of previous rhizophagy on intra-specific competitors belowground: a methodological proposal to Diabrotica speciosa (Germar)

Abstract

The cucurbit beetle, Diabrotica speciosa larvae are subterraneous and feed on plant roots, mainly Poaceae and Solanaceae. Although they are not gregarious, these larvae are often grouped in the root, triggering holes and galleries. The rhizophagy carried out by D. speciosa larvae induces the plant defense mechanisms, which can modify the behavior and development of other belowground larvae. Here, we present an induction method by natural rhizophagy of D. speciosa, which separates groups of insects into different parts of the root system. This methodology allows the prior rhizophagy by a larval group and the subsequent behavioral and performance evaluation of a larval group late affected. We cultivated maize plants in voile bags, into which 8-day-old Diabrotica speciosa larvae were inoculated. In order to determine the efficiency of the system, the weight of the larvae was measured before and after inoculation into the system. The proposed system enables normal root development of maize plants, even after their roots are wrapped in voile bags, which is possible given the porosity of the fabric used. Concerning the insects that fed on the roots inside and outside the voile bags, the fact that they presented similar weight gain indicates that they did not undergo food restriction and that the portion of the root they fed on did not influence their development during the evaluation period. Thus, insect feeding occurred normally, even if they consumed different portions of the roots. Our methodology can be used in any system that needs the simulation of rhizophagy by larvae of D. speciosa, needing to separate individuals that cause plant induction from those individuals that will be exposed to the effects of rhizophagy.