SPRUCE BUDWORM (LEPIDOPTERA: TORTRICIDAE) MOTH FLIGHT AND DISPERSAL: NEW UNDERSTANDING FROM CANOPY OBSERVATIONS, RADAR, AND AIRCRAFT

Abstract

AbstractA research programme in New Brunswick coordinating the use of radar, specially-instrumented aircraft, and observations from platforms extending above the forest canopy has established the massive scale and regularity of evening take-off flights by spruce budworm moths, Choristoneura fumiferana, and of subsequent nocturnal dispersal at levels high above the ground. A night-viewing telescope showed moths taking off from the tree crowns up until 2330 h, 2.5 h after sunset, while radar dot echoes of uniform strength and size began to appear each night at about the same time. Direct identification of radar echoes was provided by simultaneous catches of budworm moths taken in insect-collecting nets on Cessna 185 aircraft. Moths collected during emigration, displacement, and immigration contained a high proportion of egg-carrying females.Radar recorded the rates of climb and the altitudes reached by the flying moths and provided extensive data on their numbers, density, orientation, direction, speed, and duration of displacement. Airborne moths became concentrated in zones of wind convergence, and line-echoes from moths at wind-shift fronts were detected on radar at distances of 30 km. The time of passage of wind-shift fronts over a surface site was detectable by pilot-balloon observations and by sensing equipment on a 24-m meteorological tower. Wind-fields over New Brunswick, as found from a DC-3, showed a marked contrast between the high degree of wind uniformity on many evenings and convergent winds on other evenings. Attention is focussed on the potential effects of meso-scale sea breeze fronts, of which one example is presented, and of storm cells on moth concentration and dispersal.Through the use of radar, spruce-budworm moth dispersal has been viewed for the first time in its entirety and the integrated research programme has provided new data for better evaluation of the significance of moth dispersal in the initiation and spread of infestations.