The nocturnal migration of the Australian plague locust, Chortoicetes terminifera (Walker) (Orthoptera: Acrididae): quantitative radar observations of a series of northward flights

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Abstract
Night migrations of insects above the surface boundary layer were studied by direct observations with an entomological radar, and by direct aerial sampling with a kite-borne net, in an area in New South Wales inhabited by large fledging populations of Chortoicetes terminifera (Wlk.). The aerial catches and radar echo-modulation observations suggested that the majority of migrants detected by the radar were locusts, and this conclusion was supported indirectly by light-trap catches and by observations of take–off at dusk. Night flights of locusts began at dusk with a mass take-off and continued on a diminishing scale until about midnight. Displacements were all approximately downwind and to the north, under the influence of a southerly airflow which prevailed throughout the six-day study period. A quantitative radar observation procedure was used to estimate locust aerial densities and migration rates, and to observe the variations of these quantities with height and time; typical and extreme values for all the principal migration quantities are presented. The flight paths of the locusts were estimated from radar observations of target tracks, and probable source areas at distances of up to 200 km to the south were identified; a major overflight which probably originated 150 km away was detected on one occasion. Northward movements of C. terminifera during anticyclonic conditions may help to explain how populations are redistributed in the periods between the long-range southward invasion movements for which this species is well-known.

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