The Meloidae of Arizona Item Type text; Book Authors Werner, Floyd G.; Enns, Wilbur R.; Parker, Frank H. Publisher College of Agriculture, University of Arizona (Tucson, AZ) Rights Copyright © Arizona Board of Regents. The University of Arizona. Download date 30/09/2021 02:00:06 Link to Item http://hdl.handle.net/10150/607087 Technical Bulletin 175 August, 1966 The Melo/due of ár/zonu Published by the AGRICULTURAL EXPERIMENT STATION The University of Arizona Tucson The Meloidae of Arizona by Floyd G. Werner Professor of Entomology, University of Arizona Wilbur R. Enns Professor of Entomology, University of Missouri and Frank H. Parker Globe, Arizona Drawings By Martha L. Noller Research Assistant in Entomology University of Arizona OUR COVER PICTURE --- More than 100 drawings of members of the Meloidae family, or insect parts identifying various members of that family, are shown in plates at the end of this bulletin. The drawings are by Martha L. Noller of the Entomology Department. The one used on the cover is of Pyrota palpalis, also shown in Plate VIII. All plates are grouped, as we said, at the end of this bulletin. Introduction Beetles of the family Meloidae, commonly known as blister beetles, form a conspicuous element of the insect fauna of the deserts of the Southwest. The family is not easily defined, although it is easily recogniz- able in the field. The adults are mostly soft- bodied, often brightly colored. They have the head inclined, hypognathous and strongly constricted be- hind the eyes into a "neck" that does not fit entirely into the prothorax. The anterior coxal cavities are widely open behind, the anterior and middle coxae large, conical and contiguous, and the posterior coxae trans- verse. The tarsi are heteromerous, five-segmented on the anterior and middle legs, four -segmented on the posterior legs. In most members of the family the tarsal claws are cleft into two blades, with the upper blade simple or bearing a double row of fine teeth on its lower edge; in a few sections of the family the claws are simple, with a basal tooth or cleft. For general recognition the combination of soft body, constriction of head behind eyes, heteromerous tarsi and divided tarsal claws serves to distinguish most of the species commonly en- countered. The adults of many species feed on the foliage or blossoms of plants during the daytime and are thus quite conspicuous. Some other species are largely nocturnal and are rarely seen except when they congregate at lights. A few species have cryptic habits, the members of the genus Hornia rarely being found outside the burrows of solitary bees as adults. The species that feed on plant parts are often very specific in their preferences. Plants of the families Solanaceae, Leguminosae, Amaranthaceae, and Corn - positae are generally favored, but other plant families are used by some. A species sometimes feeds on only a single genus or species of plant, or even just on certain parts. Almost all the members of the subfamily Nemognathinae probably feed on nectar and pollen, and are usually found on blossoms. Many of the species in this subfamily have the galeae modified into a sucking tube. Most of the rest of the Meloidae have normal, chewing mouthparts and devour leaves, petals, etc. The food plant preference of the adults may appear very narrow under certain circumstances and very general under others. Each species ap- parently has definite preferences. If the most preferred plant is available, almost all the individuals of the species in a region are on this kind of plant. If the most preferred plant is absent, other related plants may be accepted. In some cases totally unrelated plants are devoured if the more highly preferred plants are not available. A few of our species are in bad repute from an agricultural standpoint. If there is a large hatch of adults in an agricultural area, they may feed on such plants as alfalfa and potato, even though these are not among the pre- ferred species. In the eastern half of the country there are several species that seem to prefer crop plants and some of these have become serious pests. The species that affect crop plants in Arizona have thus far caused only local damage. It is sometimes difficult to assess the food plant preference of a species in an area. When the adults first emerge, they often band together and crawl over any vegetation that may be present. By a week later they have -2 usually settled down to their preferred food plant and started to feed. At this time closely related species may become very strictly segregated onto different host plants. The collector who is interested in getting food plant information must make sure that the beetles are actually feeding and that he has not disturbed them. When he walks through mixed vegetation, most of the blister beetles drop to the ground and may or may not crawl back onto their preferred plants. The life cycle of all the blister beetles for which the details are known is quite complex. The first instar larva is an active " triungulin," so- called because there are three slender appendages at the tip of each leg. It is up to the triungulin to reach a very definite kind of food supply. All of the members of the genus Epicauta and probably all of the Epicautini feed on the eggs of grasshoppers in the larval stage; all the other groups probably feed on the stored food and eggs of wild bees. The method of gaining entry to the food supply varies. In the Epicautini, the larvae wander over the ground until they find a grasshopper egg pod. In the Meloinae and many Nemognathinae, the triungulins climb onto blossoms and ride back to the nest on visiting bees. The Iarval food and behavior are unknown for the Pyrotini and Tetraonycinae. The larvae of Lyttini feed on the stored food and eggs of bees, but the triungulin must search for the nest in the ground. If the first instar larva has been successful in finding food, it feeds and soon molts into an essentially immobile form. Later instars are like- wise immobile. One of the later instars develops a hardened skin and passes the winter thus protected. Details of the life cycle vary in the different groups. In Epicauta, the larva moves out of the food supply for a short distance before forming the hardened skin. The following year it responds to the proper moisture and temperature conditions by molting again into a normal larva, then pupating and finally emerging as an adult. In the groups associated with bees the transformations normally take place in the cell of the bee. In most species the life cycle apparently takes approximately one year, but it has been surmised that some of the species are able to remain in the stage with the hardened skin for two or more years if soil moisture does not reach a certain level. -3- Importance of Blister Beetles Medical Importance Many, perhaps all, of the blister beetles are able to cause the forma- tion of blisters on the skin of people who contact them. In Arizona this contact is most likely with the species that come to light at night. Several species found at lower elevations produce sizable blisters; Epicauta tenella and Epicauta lauta are the ones most often encountered. The blisters that are produced may be up to several inches long, and may spread if the fluid from a blister is allowed to touch unexposed skin. They soon disappear if the liquid is removed. The active principle is a substance called cantharidin. This material is present in the body, including the blood, and the main chance of human contact comes when the beetles are disturbed, at which time they can release blood through the joints of the legs. Cantharidin has a long history of use as a vesicant and as an aphrodisiac. Lytta vesicatoria, a common species in Europe, is gathered, killed and dried to form the "Spanish fly" of commerce. Agricultural Importance As has already been mentioned, several species of Arizona blister beetles have been known to attack cultivated plants as adults. The main offenders in this regard have been Epicauta pardalis, on alfalfa and potato, Epicauta andersoni on potato, and Epicauta longicollis on alfalfa. Epicauta bispinosa was involved in severe damage to tomatoes in one area in New Mexico in 1956. Several other species have been incriminated in damage to blossoms of garden flowers and leaves of shade trees, but this damage has been very local. Perhaps of greater importance is the role played by the groups other than Epicautini as "parasites" of native bees. Where these bees are of actual or potential importance as pollinators of crop and important range plants, the beetles must have a decided detrimental effect. Zonitis atri- pennis flavida has been shown to parasitize the alkali bee, Nomia melanderi, an important pollinator of alfalfa in Utah. The adult beetles frequent the blossoms of the spider plant, Cleome, which the alkali bees also visit for nectar. Triungulins of the Zonitis produced from eggs laid on the plants ride back to the nests of Nomia as passengers on the bees and complete their development there, to the detriment of the bee population. Destruction of spider plants near alkali bee nesting sites has been suggested as a means of increasing bee populations (Selander and Bohart, 1954) . Much remains to be learned about the relationship between bees and blister beetles and about the importance of native bees in Arizona. Because their larvae eat grasshopper eggs, members of the tribe Epicautini must be entered on the credit side of the ledger wherever grasshoppers cause damage to crop or range plants.