The driedfruit moth (Vitula edmandsae), and the indianmeal moth (Plodia interpunctella) are two destructive scavengers sometimes associated with cavity-nesting bees. Both cause damage in their larval stage by feeding on nectar-pollen provisions and bee larvae. In the process of tunneling between cells, the moth larva may destroy multiple cocoons, and may even chew through the walls of Styrofoam nests. Fecal pellets, massive amounts of silk webbing, and cast skins are typical signs of infestation.
Driedfruit moth adults have a wingspan of about 3⁄4 inch (19 millimeters), and are light grey with irregular grey wing markings. Females typically live up to 20 days as adults, with males only living around 10 days. Mating occurs shortly after adult emergence, and females lay up to 325 eggs beginning three days later. The cream-colored eggs are often laid in cracks and crevices around bee nests, and hatch within four to six days.
Nest invasion occurs through uncapped tunnels and along the sides of nest blocks that are drilled all the way through. From there, larvae move between nest tunnels via the back of the nest block. The larvae pass through five or six instars over a 30-day period. As it feeds, a moth larva constructs a silk-like webbed tunnel, and when disturbed will retreat into this webbing. Upon maturity the moth larvae often exit the nest and congregate in webbed clusters of up to several hundred individuals, usually located in the back or corners of nest shelters. Pupation lasts for about eleven days, and several generations can occur in a single year.
Indianmeal moth adults are reddish-brown with a metallic sheen over most of their wings, which span about 5⁄8 inch (~16 millimeters). Their body length is typically 1⁄2 inch (12.7 millimeters). Females may lay up to 400 eggs, with a lifecycle nearly identical to that of the driedfruit moth. Damage is also nearly identical to that of the driedfruit moth, and is also accompanied by feces and silk webbing. In fact, distinguishing between immature stages of the two species can be difficult for a layperson.
Control measures for both moths include tumbling of loose cells to remove moth pupae and the use of light traps during bee incubation. If nest blocks are drilled all the way through, the backing material should be held securely in place. Pheromone traps, which can be used for control of minor infestations, are also commercially available.