Assessing larval rootworm behaviour after contacting maize roots: impact of germplasm,rootworm species and diapause status

Current methods of screening maize (Zea mays L.) germplasm for susceptibility or resistance to corn rootworms (Coleoptera: Chrysomelidae) rely primarily on information from large‐scale field experiments. Due to labour and cost constraints associated with field trials, alternative evaluation methods are desirable. We used a previously developed behavioural bioassay to: (1) investigate the host search behaviour of rootworm larvae after contact with 14 maize genotypes, (2) compare the behaviour of non‐diapausing Diabrotica virgifera virgifera LeConte, diapausing D. v. virgifera, and diapausing D. barberi Smith & Lawrence and (3) determine if this technique can be used to separate susceptible vs. resistant maize genotypes. The majority of rootworm larvae engaged in intensive (local search) behaviour after exposure to maize roots, whereas larvae continued to exhibit extensive (ranging) behaviour after contact with negative controls. Even though a transgenic hybrid with resistance to D. v. virgifera was included in analyses, quantitative path measurements were similar among genotypes and only differed between specific maize lines and controls. Notably, there were differences in host search behaviour among rootworm groups, with non‐diapausing D. v. virgifera having more convoluted paths and engaging in intensive search more frequently than diapausing rootworms. Correlations between larval path measurements and historic root damage ratings were not significant, although there were weak positive correlations between historic adult emergence densities and measures of path linearity. However, due to the lack of significant behavioural differences among maize lines with a range of susceptibility levels, we concluded that this bioassay is not useful in screening maize germplasm for rootworm resistance.