The western corn rootworm Diabrotica virgifera virgifera (WCR), and the wireworm Agriotes sordidus (WW), whose eggs and first instar larvae develop in the first few centimeters of soil, are major crop pests. As soil-dwelling predatory mites are known as potential biocontrol agents against many pests, we investigated the predation capacity of Stratiolaelaps scimitus, Gaeolaelaps aculeifer and Macrocheles robustulus on immature stages of WCR and WW in a laboratory setting. While eggs of WCR and WW were never consumed, all three predator species attacked both WCR and WW first instar larvae. While these results need to be confirmed in natural conditions, our work identifies the early larval stage instead of the egg stage as the most vulnerable stage for control against WCR and WW with soil-dwelling predatory mites.

Western Corn Rootworm is a pest of maize that mostly damages roots. Many alternative strategies have been explored to control this species, with little or non-lasting success, and it remains a threat to maize production worldwide. Gaeolaelaps aculeifer, a soil-dwelling predatory mite that inhabits the first few centimeters of the soil, showed high predatory potential against WCR larvae in the laboratory. In this study, we explored the efficiency of G. aculeifer against WCR in more realistic contexts. First, we infested maize plants isolated in pots in a greenhouse with WCR, and tested the impact of different densities of mites on plant protection. Using standard indicators of WCR population presence and impact, we confirmed that G. aculeifer has the potential to control WCR at densities starting from 100 mites/plant. Then, considering that the release of a large amount of biocontrol agents at WCR emergence might be too costly and constraining for large-scale implementation, we tested the efficiency of a predator-in-first strategy in a maize field infested by WCR. The goal was to introduce fewer G. aculeifer combined with Aleuroglyphus ovatus eggs as an alternative food source in order to let the mite population grow in the field and reach sufficient density at the critical stage for protection. This strategy gave comparable results to pesticide on all indicators examined in our field trial, highlighting the potential to sustainably manage this pest.

No abstract

Soil-dwelling predatory mites already proved their efficiency as biocontrol agents against many pests (Carrillo et al. 2015). Western Corn Rootworm (WCR), (Diabrotica virgifera virgifera) and Wireworm (WW) (Agriotes sordidus) are important pests of various crops (Furlan et al. 2002;Krysan et al., 1986;Ritter and Richter 2013; Wesseler and Fall 2010) whose eggs and first instar larvae also inhabit the first centimeters of soil (Furlan 2004;Vidal et al., 2005). In order to evaluate the potential of predatory mites as biological control agents against WCR and WW, we investigated the predation capacity of Stratiolaelaps scimitus, Gaeolaelaps aculeifer and Macrocheles robustulus on immature stages of these two prey species. First, we observed if one or more species could feed upon eggs and first instar larvae as Prischmann et al. (2011) suggested for WCR. We then explored their predation abilities through time using a survival analysis to identify the best biocontrol agent among the species tested.Surprisingly, none of the predator species tested identified WCR or WW eggs as preys. However, at least 50% of WCR and WW first instar larvae have been attacked by G. aculeifer and M. robustulus. Stratiolaelaps scimitus showing a slightly lower efficiency (30% of preys attacked). The survival analysis confirmed this trend with slower predation dynamics for S. scimitus.These results show a potential of soil-dwelling predatory mites as biocontrol agents against WCR and WW. Furthermore, targeting the neonate stage instead of the egg stage in pest management strategies seems necessary for maximizing efficiency.