Bug Spotlight!

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U.C. Riverside
Department of Entomology
Photo by: Marc BoromÓ
The Iron Cross Beetle, Tegrodera aloga Skinner (Coleoptera: Meloidae)  by John D. Pinto   

The blister beetle genus Tegrodera, sometimes referred to as soldier beetles (though this common name is technically reserved for the family Cantharidae), includes three very similar species confined to Southwestern North America .  These large, colorful beetles, found primarily in late Spring and early Summer, often occur in immense feeding and mating aggregations.  Tegrodera aloga, illustrated here, ranges throughout much of the Sonoran Desert in western Arizona , extreme southeastern California and northwestern Sonora .  Tegrodera erosa LeConte is our local species.  It occurs in the dry valleys and hills of cismontane southern California and south into Baja California .  It is likely that T. erosa is undergoing considerable retrenchment in southern California as a result of unprecedented urban development of its habitat.  The third and northernmost species is T. latecincta Horn, known from the Antelope and Owens valleys.  The primary host plant for all Tegrodera species is Eriastrum (Polemoniaceae), a group of low herbaceous annuals.  However, all three species also feed readily on alfalfa where agriculture encroaches on natural lands.  Recently there has been concern about the threat that Tegrodera-contaminated alfalfa hay poses to livestock, especially horses.  As is characteristic of most meloids tested, Tegrodera hemolymph contains cantharidin, a compound toxic to mammals, which the beetles use to deter potential predators.  

Although large and conspicuous, virtually nothing is known about the larval biology of Tegrodera.  Based on data from related genera we assume that larvae feed on the provisions and immatures of soil-nesting bees.  Adult behavior includes certain interesting peculiarities.  The name soldier beetle derives from their occasional habit of following one another in single file formation.  Their common response to endangerment is the so-called “frightening attitude”.  This involves the sudden elevation of the elytra, which exposes the brilliant red abdominal intersegmental membranes, and a simultaneous rapid movement away from the stimulus.  It is suggested that such an abrupt appearance of warning coloration and the apparent increase in body size may, at least initially, intimidate potential predators.  Male courtship behavior in Tegrodera is unique.  The individual illustrated is a male as can be determined by the pair of grooved depressions on its head.  During courtship the male and female face each other, and the male grasps the female’s antennae with his own and repeatedly pulls them in and out of his head grooves where a stimulatory compound of some sort is presumably exuded.  

©2006  ERM-UC Riverside