Estimation of the expected maximal defoliation and yield loss caused by cereal leaf beetle (Oulema melanopus L.) larvae in winter wheat (Triticum aestivum L.)

Abstract

The larvae of the cereal leaf beetle (Oulema melanopus L., CLB) are one of the major pests of small grains in the Northern Hemisphere. Besides other cereals, winter wheat (Triticum aestivum L.) is among the preferred host plants of CLB larvae. In this two-year study, which was carried out in central Hungary, we examined the influence of an increasing initial number of CLB larvae on the extent of both flag leaf and all-leaf defoliation and the effects of this defoliation on the yield of winter wheat cultivars ‘Alcantara’ and ‘Altigo’. We used asymptotic nonlinear regression models for analysing the impact of the initial number of CLB larvae on flag leaf and all-leaf defoliation, and linear regression models to quantify the effect of defoliation on the yield. The asymptotic nonlinear regression models predicted mean maximal defoliation values of ca. 25% for flag leaves and ca. 20% for all leaves. In 2017, CLB defoliation had a severe impact on the yield, with 10% flag leaf defoliation causing ca. 0.17 g and 10% all-leaf defoliation causing ca. 0.241 g reduction in yield per ear for both cultivar types. However, CLB defoliation did not have any significant effects on the yield in the following study year. The predicted mean maximal defoliation levels are consistent with results reported in previous studies, whereas the strong negative effect on the yield found in 2017 is considerably higher than yield losses reported in previously published studies. Our results suggest that even high abundances of CLB larvae only cause rather low degrees of defoliation, but can still generate severe yield losses in winter wheat. However, the biological mechanisms behind both phenomena are yet unknown and highlight the need for further research.