Know Your Friends

Checkered Beetles

This predatory beetle, Thanasimus formicarius, can eat about three pine shoot beetles daily for up to 3 months. Photo by Scott Bauer, USDA.The checkered, or clerid beetles (Family Cleridae), are small beetles found primarily in woodlands. The name "checkered beetle" refers to the conspicuous colorful bands across the back of the adults. Their rounded bodies are often covered with dense, short hairs. Common species are between and inch long. There are about 250 described species in the U.S. and 2500 for the whole world. The adults are fairly long-lived and can be seen for several months during the summer.

The majority of species are predaceous on wood-boring or wood-inhabiting beetles, especially bark beetles, and are very important natural controls of these forest pests. Adult clerid beetles feed on the adult wood-borers, while the larvae prey on the immature stages, including the eggs. Other species feed on grasshopper egg pods, a few have been reported as predators of gall insects, and one genus, Necrobia, has departed from the typical food habit of the family and are primarily scavengers.

Female beetles lay eggs on wood-borer-infested trees. The eggs are usually placed in the host entrance gallery or in cracks or crevices in the bark. The red or yellow, flat or rounded larvae that hatch from the eggs are covered with hairs and have horny projections on top of one body segment. The larvae search for prey in wood-boring insect tunnels, but they, too, can bore through dead wood themselves if necessary. After they have completed their larval development many species move to the base of the tree to pupate in earthen cells, created from soil and secretions from glands inside their mouths. Others remain in their hosts' gallery or pupal cell. Development may take more than a year, or there may be one or more generations per year, depending on the life cycle of their prey. Depending on the species, the beetle may overwinter as adults, larvae or pupae.

Thanasimus dubius has been fairly well-studied, because it is an important predator of Southern pine beetle (SPB). T dubius is very well synchronized both temporaly and spatially with the SPB at the beginning of the bark beetle's attack on a tree. The clerids are attracted by the aggregation pheromone of the SPB and move rapidly around on the bark, feeding on arriving beetles. A clerid will grasp the victim from below, holding it in place with its forelegs and then rip off the bark beetle's head to consume the soft inner parts of the body. Sometimes they also separate the thorax from the abdomen, or strip off the elytra, or split the abdomen open to get to the interior. This process of dismemberment and feeding takes at least 3 minutes per prey. Each adult clerid consumes and average of 2.2 bark beetles per day. Since they live for one to two and a half months their lifetime consumption of bark beetles can be over 300. The male and female clerids also mate and lay eggs on trees undergoing mass-attack by bark beetles. A female inserts the small, white, cigar-shaped eggs individually into separate niches in the soft inner bark of the tree, usually in clusters of 2-6, extending in a fan shape from a common oviposition hole. In lab studies females laid up to 44 eggs per day (2.4 on average) with a maximum total of up to 367. The first instar larvae that hatch after 7 to 14 days enter the bark beetle galleries to search for immature beetles. During their first 2 days they consume primarily eggs, then begin eating small SPB larvae. Older larvae feed on larger SPB larvae, pupae, and recently emerged, soft adults. The larvae feed for about 2 weeks, destroying as many as 100 immature bark beetles during this period, then hollow out flattened ovoid cells in the outer bark in which to pupate. In another 2 weeks the adults emerge, to prey on emerging adult bark beetles.

Adults and larvae of Tarosetenus univittatus prey on powder post beetles that live in old, dead wood. In the forests of the western U.S. Enoclerus sphegus attacks Dendroctonus ponderosae and other bark beetles. The bright pink larvae of E. coccineus are a major predator of snakeweed root-boring insects, especially the long-horned beetle Crossidius pulchellus. Other species are being investigated as predators of house fly eggs and larvae in poultry house manure.

Grasshopper predators, such as Aulicus terrestris in the western U.S., lay their eggs singly under stones or in the soil near grasshopper egg pods. The very active larvae search through the soil for the eggs. The adults do not feed on grasshoppers, but the female beetles attack caterpillars, especially noctuids (the males do not feed at all).

Clerid beetles have been reported as important predators of many wood-boring beetles, including Asian longhorned beetle, various species of bark beetles, and other forest pests. The native clerid T. dubius will attack several species of bark beetle besides SPB, including larvae of pine shoot beetle, an introduced bark beetle, in brood logs. It has been shown to be an important predator of the pine engraver, Ips pini, in the upper Midwest. Predation by this beetle on SPB is most effective in the spring, when overwintering populations of SPB are emerging to begin the first breeding cycle of the season. However, the clerid does not reproduce as rapidly as its host (completing only 2.5 to 4 generations/year, while the SPB goes through 6 to 8 generations/year) so it is probably incapable of preventing epidemics. It can, however, contribute to bark beetle population declines.

The USDA was rearing T. formicarius, a European predator of pine shoot beetle, as well as T. dubius, for biological control of that pest (until that project was terminated). T. formicarius is attracted to odors from damaged Scots pine as well as bark beetle pheromones. They consume up to 10 adult beetles daily.

Clerid beetles sense the pheromones produced by bark beetles to help them locate their prey. Trap-out of bark beetles using aggregation pheromones sounds like a good idea, but it doesn't remove enough of the beetles and can interupt natural predator efficacy. Trapping has actually extended outbreaks in some cases.

— Susan Mahr, University of Wisconsin - Madison

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