Efficacy of entomopathogenic nematodes used for control of stable flies (Stomoxys calcitrans) at round bale feeding sites in pastures

Stable flies (Stomoxys calcitrans), are one of the most important pests of pastured cattle. Sites where round bales are fed have shown to be significant habitat for stable fly development during spring and summer. Two species of nematodes, (Steinernema glaseria and Heterorhabditis heliothidis), were administered to the feeding location. Five replications (1 control, 4 treatments) were constructed at four locations. Cone traps at the feeding sites were seeded with 500 fly eggs in early June and 100 first to second instar larvae in early July. Nematode treatments were administered one day after seeding with four separate ratios of nematodes totaling 75,000 infective juveniles in one liter of water. The emergence of stable flies from each site was sampled twice weekly from June 1st to late July. Nematodes used in the trial are naturally occurring species in the region, and are not host specific predators. Nematodes enter the fly larvae and introduce Xenorhabdus spp. bacterium, which attacks the entrails of the larvae. They then feed on the bacteria and reproduce; once the host is consumed generations of infective juveniles emerge and begin the search for new hosts. By increasing the population of nematodes at the feeding sites, a decrease in adult flies is expected.