Use of Dichlorvos Resin Strips to Reduce Parasitism of Alfalfa Leafcutter Bee (Hymenoptera: Megachilidae) Cocoons During Incubation

Uninfested cocoons of the alfalfa leafcutter bee, Megachile rotundata (F.), bare prepupae, and cocoons infested with the chalcidoid, Pteromalus venustus Walker, were exposed to vapor from dichlorvos resin strips at rates of 0.16, 0.37, 0.71, and 0.99 strip per 28.3 m3 during 4 days of incubation. For uninfested cocoons, there was no significant reduction in leafcutter bee survival at the dichlorvos rates tested. For bare prepupae, there was a significant linear trend of reduced survival with increased dichlorvos rate. Cocoons apparently protect the bees from dichlorvos vapor. For infested cocoons, 0.71 strip per 28.3 m3 reduced the parasitism from 40 to 13% which significantly increased bee survival. Adult parasites were placed in different housing environments and exposed to the 0.71 strip per 28.3 m3 rate. When parasites were directly exposed to dichlorvos vapor, mortality occurred within 2 h. When parasites were shielded by layers of cocoons, mortality was delayed 7 to 10 h. Because 25% parasitism can occur within 4 h of P. venustus emergence, it is unlikely that dichlorvos resin strips alone will totally control parasitism in a commercial operation.