Evidence from traditional and new technologies for northward migrations of Australian plague locusts (Chortoicetes terminifera) (Walker) (Orthoptera: Acrididae) to western Queensland

Abstract

The development of recent infestations of the Australian plague locust ( Chortoicetes terminifera ) (Walker) (Orthoptera: Acrididae) has been traced using traditional survey data combined with information from several modern technologies including simulation of windborne transport trajectories, direct observation with entomological radar and satellite imagery. The results indicate that migration from spring generations in the southern and eastern parts of the species range, including agricultural areas, to the summer rainfall areas in arid western Queensland (Qld) has contributed to the development of infestations on several occasions. Migration from swarm populations in New South Wales to western Qld in November and December 1999 contributed to a rapid population increase that, over a sequence of generations, led to the major infestation of agricultural areas in March and April 2000. There is evidence that northward migrations also occurred in 1995, 1997 and 2000. These contributed to the early summer populations in Qld, but did not result in large migrations to the south in autumn. These observations suggest that a pattern of exchange migration across much of the geographical range of the species between regions of winter and summer rainfall characterizes the spatial dynamics of this species. This pattern appears to be adaptive and suggests migration in C. terminifera is sustained by contemporary natural selection.

Recognition and characterization of migratory movements of Australian plague locusts,Chortoicetes terminifera, with an insect monitoring radar

“…7(b) indicates that few insects flew further than 400 km. This small, singleseason study shows a predominance of movements with a westward component; this is consistent with previous analyses, drawing on data from earlier years, of C. terminifera-type targets at this site 24 [which is at the eastern edge of the region where the seasonal northward and southward movements 4 predominantly occur]. The movements from the east can be attributed to the populations recorded by conventional methods at a distance of ∼300 km in that direction and fledging during this period (see above).…”

“…Perhaps their most significant contribution, however, has been as one of the sources of evidence that led to the recognition that northward flights of C. terminifera in late spring and early summer, previously dismissed as insignificant, are an important element of the species' annual cycle. 4 These "return migrations" are now understood to "seed" the subtropical (summer rainfall) rangelands of the far inland where population build-up can be rapid and lead to an outbreak. 5 This insight has strengthened APLC's capacity to undertake strategic control and thus accumulation of long-term statistics by the IMRs has proved as valuable as their direct operational/sentinel role.…”

“…They are also incorporated into a multiple-year accumulating dataset that forms the basis for analyses of movement patterns, of seasonal and year-to-year variations, and of correlations with environmental variables. 4,10 The type of information about locust populations that a radar provides differs in several ways from that available from more conventional sources. In particular, the insects being observed are inaccessible-they can be over 1 km above the surface-and thus no specimens are available to confirm their identity.…”

“…In eastern Australia, movements tend to be northward in spring, out of temperate-zone regions with winter rainfall, and southward in autumn out of the adjacent subtropical summer-rainfall zone. 1,4 Populations in the subtropical rangelands of southeastern Queensland can grow rapidly in years with high summer rainfall, and this area is often regarded as the source of major outbreaks and plagues. 5 The main management strategy for this species is pre-emptive control in the inland, with the aim of suppressing, or at least reducing, population build-up before the locusts move southwards or eastwards into the cropping belt.…”

Challenges to assessing connectivity between massive populations of the Australian plague locust

“…Given its broad geographical range and potential to mass migrate, an improved understanding of its movement patterns and population dynamics is of critical importance to its management. Locust populations have been monitored independently in Western Australia (by the Western Australia Department of Agriculture) and in the four eastern states of Australia (by the Australian Plague Locust Commission), largely assuming low demographic connectivity between populations from both sides of the continent [23,24]. However, the demographic independence of outbreak events at the continental scale has been questioned since the first report of simultaneous locust plagues in 1999-2000 at both the eastern and western extremes of the species's distribution [25].…”