true bug

Western conifer seed bug

Western conifer seed bugs (Leptoglossus occidentalis) are true bugs (Hemiptera) in the family Coreidae. It was originally native to the warm-temperate western USA (California, Oregon and Nevada) but has in recent times expanded its range and become an invasive species in parts of Europe.

This species is sometimes coloquially called "the leaf-footed bug", but actually leaf-footed bugs are an entire group of species in Leptoglossus and related genera of the Coreidae; see for example the Florida Leaf-footed Bug, L. phyllopus.

Description

The average length is 16-20 millimetres, with males being smaller than females. They are able to fly, making a buzzing noise when airborne. Western conifer seed bugs are somewhat similar in appearance to the Wheel Bug (Arilus cristatus) and other Reduviidae (assassin bugs). These, being Cimicomorpha, are not very closely related to leaf-footed bugs as Heteroptera go; though both have a proboscis only the assassin bugs bite even if unprovoked, and L. occidentalis like its closest relatives can be most easily recognized by the expanded hindleg tibiae and by the alternating light and dark bands which run along the outer wing edges on the flaring sides of the abdomen. Their primary defense is to spray a bitter, offending smell; (though sometimes they can smell pleasantly of apples) however, if handled roughly they will stab with their proboscis, though they are hardly able to cause injury to humans as it is adapted only to suck plant sap and not, as in the assassin bugs, to inject poison.

Ecology

In its native range the Western Conifer Seed Bug feeds on the sap of developing conifer cones throughout its life, and its sap-sucking causes the developing seeds to wither and misdevelop. It is therefore considered a minor tree pest in North America, but becoming sometimes more harmful e.g. in conifer plantations. However, it is not monophagous and even adaptable enough to feed on angiosperms if it has to, though it seems to prefer resiniferous plants that are rich in terpenes. As these are produced by plants to deter herbivores, it might be that in evolving its ability to overcome these defences, L. occidentalis actually became somewhat dependent on such compounds.

Its hostplants in the native range includes conifers like the Lodgepole Pine (Pinus contorta), the White Spruce (P. glauca), and the Coast and Rocky Mountain Douglas-firs (Pseudotsuga menziesii). Outside the native range it is also found on species like the Eastern White Pine (P. strobus) and Red Pine (P. resinosa) in eastern North America and Europe, and the Mountain Pine (P. mugo), European Black Pine (P. nigra), Scots Pine (P. sylvestris) and Pistachio (Pistacia vera) (pistaches or pistacio trees) in Europe.

The eggs are laid in small groups on the needles or leafstems of its host plants, and hatch in spring. The nymphae go through 5 instar stages before moulting into adults. In the USA the species is univoltine, but in southern Europe it completes two generations a year, and in tropical Mexico even three. In the northern parts of its range, these bugs start to move about widely by September or so to seek crevices for overwintering; they may become a nuisance in areas with extensive conifer woods as they will sometimes enter houses in considerable numbers.

Range and invasiveness

This insect is common in its native range along the temperate and warmer regions of the Pacific coast of North American and has steadily expanded eastwards. On its native continent, L. occidentalis has been located as far northeast as Maine.

In Europe this species was first reported in 1999 from northern Italy; it had probably been accidentally imported with timber and as it seems more than once, as its presence was subsequently reported from that country almost simultaneously from locations a considerable distance apart. By 2007, it had established itself in the northern Balkans (Slovenia] and Croatia, the Alps (Austria, Switzerland,), and parts of the Czech Republic, France, Germany and Hungary; in 2003 it was found to occur in Spain though this population probably derives from a separate introduction. The 2007 records from Weymouth College (England) and Oostende (Belgium) might also represent one or two further independent introductions. In late 2007, it was found at Wrocław and Miechów (Poland); these animals probably represent a further range expansion out of the Czech Republic.

Footnotes

References

This article draws heavily on the Leptoglossus occidentalis in the Italian-language Wikipedia.

(2006): Kaufman field guide to insects of North America. Houghton Mifflin Co. ISBN 0-618-15310-1
(2008): Will the invasive western conifer seed bug Leptoglossus occidentalis Heidemann (Hemiptera: Heteroptera: Coreidae) seize all of Europe? Zootaxa 1740: 66–68.