Recent Insights from Radar Studies of Insect Flight

Abstract

Radar has been used to study insects in flight for over 40 years and has helped to establish the ubiquity of several migration phenomena: dawn, morning, and dusk takeoffs; approximate downwind transport; concentration at wind convergences; layers in stable nighttime atmospheres; and nocturnal common orientation. Two novel radar designs introduced in the late 1990s have significantly enhanced observing capabilities. Radar-based research now encompasses foraging as well as migration and is increasingly focused on flight behavior and the environmental cues influencing it. Migrant moths have been shown to employ sophisticated orientation and height-selection strategies that maximize displacements in seasonally appropriate directions; they appear to have an internal compass and to respond to turbulence features in the airflow. Tracks of foraging insects demonstrate compensation for wind drift and use of optimal search paths to locate resources. Further improvements to observing capabilities, and employment in operational as well as research roles, appear feasible.

Seasonal migration to high latitudes results in major reproductive benefits in an insect

“…We estimated the migratory flux rates of high-flying A. gamma moths engaged in spring migration into the United Kingdom and fall (return) migration out of the United Kingdom, using data collected by two purpose-built, vertical-looking entomological radars (VLR) situated in southwest and southeast United Kingdom 1′ 27′′ W) from 1999 onward. The VLR equipment and operating procedures are described in detail elsewhere (9,45,46). Briefly, the radars provide a range of information-including body size, flight altitude (insects are detected within 15 separate altitude bands), aerial density, displacement speed, displacement direction, and flight heading-for all individually resolvable insects of > 2 mg body mass that fly through the vertically pointing beam within the altitude range of ∼150-1,200 m above the radar site.…”

“…Numerous insect species, comprising members of several insect orders, migrate poleward from lower-latitude winter habitats each spring to exploit temporary resources where they can reproduce during the summer but are unable to survive over winter (2)(3)(4)(5)(6)(7)(8)(9). Compared with our knowledge of the energetic costs, mortality risks, and reproductive benefits of bird migration (10)(11)(12)(13)(14)(15)(16), the adaptive benefits and population dynamics consequences of insect migration are poorly understood (6)(7)(8)(9). For most migratory insects, their low-latitude winter habitats are considered to be the major breeding grounds.…”

“…In fact, some authors have previously suggested that seasonal poleward shifts to exploit temperate ecosystems represent a population sink from which progeny seldom returned: a phenomenon known as the "Pied Piper" effect (17,18). This notion made little evolutionary sense, however, and has been contested (7,8,19); moreover, return flights have been observed in many species (5,(7)(8)(9)(20)(21)(22)(23)(24)(25). However, it is unclear whether highlatitude breeding results in net reproductive benefits to migrating species or whether significant proportions of the progeny produced over the summer successfully make it back to regions where they can breed again, and there is no information on population sizes and migration intensities between zones.…”

“…However, it is unclear whether highlatitude breeding results in net reproductive benefits to migrating species or whether significant proportions of the progeny produced over the summer successfully make it back to regions where they can breed again, and there is no information on population sizes and migration intensities between zones. These are vital issues because billions of insects immigrate annually to, or within, the temperate zone, providing major ecosystem services as well as, in some cases, causing serious crop damage and spreading diseases of humans and their livestock (9).…”

“…To distinguish between these hypotheses, we used a national network of light traps (32) to quantify intra-and interannual variation in A. gamma populations at ground level during 1976-2009 and specially developed vertical-looking entomological radars (9) to quantify the intensity of high-altitude migrations into and out of the United Kingdom in [2000][2001][2002][2003][2004][2005][2006][2007][2008][2009] (Fig. 1).…”