Movement of plum curculio adults toward host trees and traps: flight versus walking

Adult plum curculios, Conotrachelus nenuphar (Herbst), were dislodged from branches of apple trees by tapping on 14 days between blossom petal fall and 3 weeks thereafter. They fell onto a small square of framed white cloth that was quickly but carefully moved to a position beneath or adjacent to the canopy of another apple tree.There, adults were observed for 50-min periods from 0800–1950 h for propensity to fly from or walk off the cloth or move to hide beneath foliage on the cloth. At each position, the mean time from observation initiation until flight, walking off or hiding did not differ significantly among these behaviors (averaging 21–30 min), but significantly more flew (31–40%) than crawled off (16–19%) or hid (18–20%). Substantial walking off but no flights occurred at air temperatures below 20 °C, whereas at temperatures of 20 °C or greater, propensity for flight was usually significantly greater than that for walking off.Flights were predominantly toward the tree canopy or inter-tree space, with only a small proportion (17% or less) toward the tree trunk or (in a parallel study) toward an unbaited black pyramid trap (mimicking a tree trunk). Walking was overwhelmingly toward the tree trunk or a black pyramid trap adjacent to the trunk. Our observations lead us to conclude that unbaited black pyramid traps next to trunks of host trees (the most attractive position) can be effective at air temperatures below 20 °C by attracting plum curculio adults that would have entered host trees by walking toward and up tree trunks.Such traps appear to be less effective at 20 °C or greater because under such conditions, adults tend to enter host trees by flight into the canopy.