FOREST ANT COMPOSITION AND FORAGING FOLLOWING AERIAL SPRAYING OF CARBARYL TO SUPPRESS WESTERN SPRUCE BUDWORM
AbstractAn outbreak of western spruce bud worm, Choristoneura occidentalis Freeman, in the Blue Mountains of eastern Oregon, USA, was treated with helicopter-applied carbaryl. Effects on forest ants were determined from pre- and post-spray samples taken from replicated 0.75-ha sprayed and unsprayed plots. Arboreally foraging ants were sampled with sticky drop traps placed under trees. Ground-foraging ants were sampled from food-baited boards. During 8 weeks of sampling, 13 225 ants from seven genera and 19 species were collected. Seven species were known budworm predators. After spraying, ant species diversity decreased in sprayed plots. Post-spray foraging decreased in all plots, but the decrease was more rapid and pronounced in sprayed plots. Among ground-foragers, budworm predators were clearly affected by spraying. Arboreal foragers, nearly all budworm predators, showed a significantly lower foraging rate in sprayed plots. Varying effects on different species were noted. Overall ant foraging remained depressed for at least 6 weeks after spraying, long enough for budworm development to be completed. Reduced ant predation on sparse budworm populations after spraying may contribute to budworm resurgence.