Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2016
Publication Date: 8/12/2016
Citation: Pitts Singer, T., Barbour, J.D. 2016. Effects of residual novaluron on reproduction in alfalfa leafcutting bees, Megachile rotundata F. (Megachilidae). Pest Management Science. doi: 10.1002/ps.4356.

Interpretive Summary: Knowledge of lethal and sublethal pesticide effects on pollinators allows for prudent decision-making in cropping systems that require pollination. The insect growth regulator novaluron is used to control certain coleopteran, lepidopteran, hemipteran, and dipteran pests. Although novaluron is considered a reduced risk insecticide because it disrupts an insect’s ability to molt and leads to death of only immature stages, some exposed adult beneficial insects produce fewer eggs and experience suppressed egg hatch. Novaluron can be used to suppress pests in the alfalfa seed production system, but can have negative impacts on the reproductive success of the primary managed alfalfa pollinator Megachile rotundata, the alfalfa leafcutting bee. This study was performed to assess the persistence of novaluron effects on leafcutting bees and to better understand novaluron exposure routes for eggs and larvae. Bees nested in field cages where they were exposed to alfalfa that had not been treated with novaluron (control cages), had recently been sprayed, or had been sprayed one- and two-weeks earlier. Compared to the control, we found greater proportions of cells with dead eggs and larvae and lower proportions of live prepupae, regardless of whether nesting female bees were exposed to one- or two-week old novaluron residues, revealing lingering effects of this pesticide. Beyond pollen and nectar serving as direct routes of pesticide exposure, other routes were considered. First, the mother bee becomes contaminated internally through ingestion or direct contact. Second, the pollen-nectar provision becomes contaminated 1) with novaluron that is on or within the leaf pieces that surround the provision or 2) with novaluron carried on the mother bee’s body that transfers to the provision. Both exposure routes explain outcomes in this study. Understanding all possible routes of pesticide exposure to crop-pollinating leafcutting bees will enhance decision-making for maintaining bee health and reproductive success while protecting the crop from pests.

Technical Abstract: Knowledge of lethal and sublethal pesticide effects on pollinators allows for prudent decision-making in cropping systems that require pollination. The chitin synthesis inhibitor novaluron is used to control certain coleopteran, lepidopteran, hemipteran, and dipteran pests. Although novaluron is considered a reduced risk insecticide because it disrupts insect ecdysis and leads to death of only immature stages, some exposed adult beneficial insects produce fewer eggs and experience suppressed egg hatch. Novaluron can be used to suppress pests in the alfalfa seed production system, but can have negative impacts on the reproductive success of the primary managed alfalfa pollinator Megachile rotundata F. (Hymenoptera: Megachilidae). This study was performed to assess the persistence of novaluron effects on M. rotundata and to better understand novaluron exposure routes for eggs and larvae. Bees nested in field cages where they were exposed to alfalfa that had not been treated with novaluron (control cages), had recently been sprayed, or had been sprayed one- and two-weeks earlier. Compared to the control, we found greater proportions of cells with dead eggs and larvae and lower proportions of live prepupae, regardless of whether nesting female bees were exposed to one- or two-week old novaluron residues, revealing lingering effects of this pesticide. Beyond pollen and nectar serving as direct routes of pesticide exposure, other routes were considered. First, the mother bee become contaminated internally through ingestion or direct contact. Second, the pollen-nectar provision become contaminated 1) with novaluron that is on or within the leaf pieces that surround the provision or 2) with novaluron carried on the mother bee’s body that transfers to the provision. Both exposure routes explain outcomes in this study. Understanding all possible routes of pesticide exposure to crop-pollinating M. rotundata will enhance decision-making for maintaining bee health and reproductive success while protecting the crop from pests.