There is currently a great deal of concern about population declines in pollinating insects. Many potential threats have been identified which may adversely affect the behaviour and health of both honey bees and bumble bees: these include pesticide exposure, and parasites and pathogens.
Whether biological pest control agents adversely affect bees has been much less well studied: it is generally assumed that biological agents are safer for wildlife than chemical pesticides. The aim of this study was to test whether... nematodes sold as biological pest control products could potentially have adverse effects on the bumble bee... One product was a broad spectrum pest control agent... the other product was specifically for weevil control...
Both nematode products caused ≥80% mortality within the 96 h test period when bees were exposed to soil containing... nematodes at the recommended field concentration... Of particular concern is the fact that nematodes from the broad spectrum product could proliferate in the carcasses of dead bees, and therefore potentially infect a whole bee colony or spread to the wider environment.
https://dx.doi.org/10.7717/peerj.1413
Via Alexander J. Stein