Dispersal of Warren Root Collar Weevils (Coleoptera: Curculionidae) in Three Types of Habitat

Abstract

Warren root collar weevil, Hylobius warreni Wood, is a native, flightless insect distributed throughout the boreal forest of North America. It is an emerging problem in young plantings of lodgepole pine, Pinus contorta variety latifolia, in western Canada, where larval feeding can kill young trees by girdling the root collar. Susceptible plantings are becoming more abundant following salvage harvesting and replanting activities in the wake of an ongoing epidemic of mountain pine beetle, Dendroctonus ponderosae (Hopkins). Previous studies using mark-trap-recapture methods found that movement rates of adult H. warreni were elevated in areas with high numbers of dead trees, consistent with a hypothesis that the insects immigrate from stands with high mountain pine beetle-caused tree mortality to young plantings in search of live hosts. Sampling methods were necessarily biased to insects captured in traps; however, potentially missing individuals that had died, left the study area, or simply remained stationary. Here, we used harmonic radar to examine weevil movement in three different habitats: open field, forest edge, and within a forest. We were able to reliably monitor all but two of 36 insects initially released, over 96 h (4 d). Weevils released in the open field had the highest rates of movement, followed by weevils released at the forest edge, then weevils released within the forest. Movement declined with decreasing ambient air temperature. Our results suggest that weevils tend to be relatively stationary in areas of live hosts, and hence may concentrate in a suitable area once such habitat is found.

The role of vision in the host orientation behaviour of Hylobius warreni

“…Visual cues are often important in short range host selection, from distances of a few centimetres up to 10 m (VanderSar & Borden, 1977; Bernays, 2003). Movement by adult Warren root collar weevils falls within this range because the insects traverse a mean distance of up to 2 m per night (Cerezke, 1994; Klingenberg et al , 2010a; Machial et al , 2012). Flightless insects may not be as dependent upon long‐distance (i.e.…”

Host condition effects upon Agrilus planipennis (Coleoptera: Buprestidae) captures on decoy-baited branch traps

“…Modeling of insect dispersal through forest habitats of varying quality has been of interest in a number of systems, and has often been studied by techniques such as mark-recapture (Vairkonyi et al, 2003) and radar detection (Machial et al, 2012). Differences in dispersal rates that vary with habitat quality have been observed in such studies (Klingenberg et al, 2010).…”

Random and Directed Movement by Warren Root Collar Weevils (Coleoptera: Curculionidae), Relative to Size and Distance of Host Lodgepole Pine Trees

“…For example, Cerezke (1994) found that when weevils were captured at different trees on successive nights, the mean dispersal distance/night closely matched the mean distance between trees within the stand. In addition, observed movement rates are higher in unfavorable habitats such as those with dead trees ( Klingenberg et al 2010b ), or in an open field ( Machial et al 2012b ), when compared with movements in more favorable habitats with live trees. Finally, weevils that are released and not in contact with appropriate host trees tend to have movement rates that decline with time, suggesting that the weevil’s movements may function primarily to locate host trees, and then decrease once suitable resources have been located ( Klingenberg et al 2010b , Machial et al 2012b ).…”

“…Insects may seek out hosts for differing reasons, such as food, shelter, location of mates, or oviposition, depending on species, as well as on the individual’s internal state, such as hunger status or degree of sexual maturity, and external factors, such as weather or presence of predators ( Laing 1937 ). Previous work has suggested a strong random component to H. warreni movements, as the weevils’ movements have been observed to be non-directional in unfavorable environments including habitats with dead trees ( Klingenberg et al 2010b ) and an open field ( Machial et al 2012b ). Similarly, Schroff et al (2006) found that the spatial distribution of weevil attacks in lodgepole pine plantations appeared to be randomly distributed, rather than aggregated or clumped.…”

“…Harmonic radar was first adapted from its original purpose (location of avalanche victims) and described for use to track insects by Mascanzoni and Wallin (1986) . The system works by a hand-held detector emitting a microwave beam (917 MHz), which a transponder (Schottky barrier diode attached to a metal wire antennae) attached to the insect passively reflects back at twice the frequency ( Machial et al 2012b ). Since it is a passive system, the transponder does not need an attached energy source like more traditional radio transmitters, and thus can be light and small enough to use with insects ( Lövei et al 1997 , Reynolds and Riley 2002 ).…”