Field survival analyses of adult Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae)
2015
Toepfer, Stefan | Zellner, Michael | Szalai, Mark | Kuhlmann, Ulrich
The western corn rootworm (Diabrotica virgifera virgifera; Coleoptera: Chrysomelidae) is a major maize pest in North America and Europe. For developing population models to better understand this key pest, survival rates need to be known. In contrast to the reported field survival of eggs, the three larval instars, and pupae, the survival of the adults had not been assessed under field conditions. Weekly survival of adults was studied in large walk-in gauze cages in two fields in Hungary between 2009 and 2011. Each cage contained a combination of maize with two out of nine other crops. The number of adult beetles rapidly decreased with time following an exponential-like survivorship curve, with a weekly mortality varying between 31 and 61 %. This is in contrast to laboratory experiments, where populations decreased with time following a linear-like curve. The average lifespan was only 19 days with a maximum of 84 days. After 14 days, 55 % of adults had died, thus, having had no chance to lay eggs because of the pre-oviposition period required. Maize appeared to be the most appropriate crop for survival. Combining maize with other crops that could serve as alternative food did not enhance survivorship, and many combinations were in fact disadvantageous. Crop and weed coverage played a minor role in influencing survival, and only few weeds appeared slightly advantageous. It is argued that the role of alternative food sources for D. v. virgifera adults might be overestimated. Survivorship equations are suggested to support modelling of population dynamics of this pest and to support timing of direct control measures against the adults to prevent their egg laying and therefore damage to maize roots the following year.
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