Assessing Larval Rootworm Behavior after Contacting Maize Roots: Impact of Germplasm, Rootworm Species, and Diapause Status

Authors: Prischmann, Deirdre; Dashiell, Kenton; Hibbard, Bruce

Submitted to: Journal of Applied Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/17/2008
Publication Date: 8/27/2008
Citation: Prischmann, D.A., Dashiell, K.E., Hibbard, B.E. 2009. Assessing Larval Rootworm Behavior after Contacting Maize Roots: Impact of Germplasm, Rootworm Species, and Diapause Status. Journal of Applied Entomology. 133:21-31.

Interpretive Summary: 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 labor and cost constraints associated with field trials, alternative evaluation methods are desirable. We used a previously developed behavioral bioassay to: 1) investigate the host search behavior of rootworm larvae after contact with 14 maize genotypes, 2) compare the behavior 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 versus resistant maize genotypes. The majority of rootworm larvae engaged in intensive (local search) behavior after exposure to maize roots, whereas larvae continued to exhibit extensive (ranging) behavior 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 between genotypes, and only differed between specific maize lines and controls. Notably, there were differences in host search behavior between 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 behavioral differences between maize lines with a range of susceptibility levels, we concluded that this bioassay is not useful in screening maize germplasm for rootworm resistance.

Technical Abstract: 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 labor and cost constraints associated with field trials, alternative evaluation methods are desirable. We used a previously developed behavioral bioassay to: 1) investigate the host search behavior of rootworm larvae after contact with 14 maize genotypes, 2) compare the behavior 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 versus resistant maize genotypes. The majority of rootworm larvae engaged in intensive (local search) behavior after exposure to maize roots, whereas larvae continued to exhibit extensive (ranging) behavior 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 between genotypes, and only differed between specific maize lines and controls. Notably, there were differences in host search behavior between 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 behavioral differences between maize lines with a range of susceptibility levels, we concluded that this bioassay is not useful in screening maize germplasm for rootworm resistance.