Volume II, no. 1, Spring 1993Table of Contents
Hydrophilids; habitats, common names and their
biology Hydrophilids; Habitats, Common Names and Their BiologyThe most common name given to hydrophilids (at least in English speaking countries) is "water scavenger beetles". This common name is sometimes misleading, because it only applies to the aquatic or semiaquatic species of the family. Probably about half of the species within the Hydrophilidae are terrestrial, being usually found in dung, rotting mushrooms, and other kinds of decaying organic matter. If we were to give common names to these terrestrial species based on the habitats in which they occur, we would apply names like "dung beetle", "scavenger fungus beetle", etc. (These names are not handsome or pleasing, but they sound familiar). In some cases the habitats of certain species or even genera are not well known, even though many of these are readily collected at lights or traps. This shows how little our beetle fauna has been studied from the bionomical or ecological point of view. Traditionally studies have been conducted with preserved museum specimens. This leaves the biology of the beetles completely unstudied. This does not mean I am against the study of museum specimens (I also work with them). It is not just how an insect looks. We must not forget that it is more important to understand the way in which an insect lives and its impact in the ecosystem. To give a brief idea of the diversity of habitats that hydrophilids occupy a general description of the bionomics of the different subfamilies is given. There are eight subfamilies in the United States: 1. Helophorinae: one genus, Helophorus. Adults are aquatic, semiaquatic and terrestrial, occurring in shallow standing waters and streams, in wet debris or mud near water and at the base of plants such as turnips (living in holes made in the stem). Adults are phytophagous, feeding mainly on algae or plant tissues. Females lay eggs in a silk case using a variety of substrates. Larvae are predaceous, and feed on small invertebrates and larvae of other insects. Some of the species in this genus are parthenogenetic. 2. Epimetopinae: one genus, Epimetopus. Adults and larvae occur in littoral situations, among plants or debris on the shore. At least one species lives on the margins of warm streams (100F) in Arizona. Females lay eggs in a silk case and carry them on the underside of the abdomen. Nothing else is known about the biology of this group. 3. Chaetarthriinae: one genus, Chaetarthria. These are very small beetles which burrow in the sand on the margins of streams or rivers. Females lay eggs in a silk case. Larvae live in the same habitats and few are found in the water. Nothing else is known about the biology of this group. 4. Hydrochinae: one genus, Hydrochus. They live on the vegetation in standing or slow running waters. Females lay eggs in silk cases. Larvae also live on aquatic vegetation, but nothing is known of their food habits. 5. Hydrophilinae: small to large beetles, with several genera in this group. All adults are very good swimmers and live in all kinds of aquatic situations, feeding on the vegetation, algae and also dead organisms. Females produce silk cases which contain from a few eggs to more than a hundred, depending on the species; the egg cases may be attached to a substrate or float freely. Larvae are good swimmers, and all are predaceous; they cling to the vegetation waiting for prey. 6. Berosinae: two genera in the U.S., Berosus and Derallus. Adults are aquatic and good swimmers; they feed on decaying vegetation and algae. Females lay eggs in silk cases which are attached to the vegetation. Larvae of Berosus are benthic, living in the mud at the bottom of standing waters or slow running streams; they breath through abdominal tracheal gills. Larvae of Derallus live on the aquatic vegetation, and breath atmospheric air, lacking tracheal gills, but have the body covered by large and spiny projections. Larvae of both genera are predaceous. 7. Hydrobiinae: many genera, usually small beetles. Adults are scavengers, and are poor swimmers; they live in littoral situations, on the aquatic vegetation or on the margins of rivers, streams or standing waters. Females lay eggs in silk cases on different substrates, in some cases the egg cases can be carried on the underside of the abdomen (Helochares) or in a few cases it is reduced to only a few strands of silk around the eggs (Cymbiodyta). Larvae are predaceous, and occur in the same habitats as the adults. The biology of several genera is not well known. 8. Sphaeridiinae: many genera, and the most species-rich and least known group of hydrophilids. Mainly terrestrial, but there are a few aquatic and semiaquatic species (some live in bromeliads). Terrestrial species occur in different situations such as decating plant material, mushrooms, dung or ant nests (please do not mistake these with disgusting creatures such as histerids). Females lay silk egg cases on a variety of substrates. Larvae are all predaceous, feeding mainly on fly larvae that occur in the same habitats. The biology and immature stages of several genera is still unknown. As it can be seen from this short note, there are still many groups that require a lot of research. In a recent paper A. Newton (1990) provides some statistical information about Staphyliniformia larvae. According to Newton only 30.6% of the world genera, and only 5.9% of the world species of hydrophilids have been described. This estimate only refers to descriptions, not detailed studies on the biology, ecology, or behavior of these beetles. This makes hydrophilids (and many other families of beetles too) an important source of work for young and enthusiastic entomologists. Reference: Newton, A. F. Jr. 1990. Larvae of Staphyliniformia: Where do we stand? Coleopts. Bull. 44(2): 205-210. - Miguel Archangelsky A Shortcut to Wood-BorersAs winter nears an end, and spring looms on the horizon, a productive technique for obtaining wood-boring beetles presents itself. Rearing specimens from their host woods is an easy way to obtain species not readily found in the field. It also provides invaluable biological data about the species being reared. Many Cerambycidae overwinter as larvae and pupate in late winter or early spring, making this time of year ideal for bringing wood indoors. Larvae have endured sufficient cold to successfully pupate and often transform quickly when brought inside. The pupal stage is often slightly shortened as well, with adults often emerging earlier then they would outdoors. Some species, such as Stenosphenus notatus (Olivier), overwinter as unemerged adults and will emerge from the host after only a few days indoors. Many interesting species are more easily obtained through rearing than by other collecting techniques in the field. I have reared several dozen adults of Xylotrechus quadrimaculatus (Haldeman), a small clytine, from the beech (Fagus sp.) branches that its larva prunes, but have not seen a single adult in the field! Phymatodes amoenus (Say), a pretty little blue callidiine, can be reared in large numbers from dead grape (Vitis sp.) vines, but is seldom encountered on this host in the field as an adult. The same is true of S. notatus, which is usually reared from dead hickory (Carya sp.). As well as specimens, rearing can provide important biological data. Associating adults with their hosts is the most obvious advantage to rearing, but information such as life cycle length, feeding habits and emergence data can be recorded. Be cautious, however, to keep in mind that emergence times and lengths of feeding times can be artificially altered by too drastic a change from the normal outdoor temperature and moisture levels. Often several species may be regularly found in association with each other in a particular host, utilizing different parts of the wood. P. amoenus is usually associated with the clytine, Clytoleptus albofasciatus (Castelnau & Gory), the latter normally occurring in much lower numbers. Hickory usually is infested with S. notatus and Graphisurus despectus LeConte, an acanthocinine, both of which bore under the bark, and Neoclytus mucronatus (Fab.), a clytine, which bores in the sapwood. It is not unusual to get Dicerca spp. (Buprestidae) from this host as well, these utilizing the heartwood. Rearing observations can be extrapolated to help explain some of the adult habits in the field. Both S. notatus and P. amoenus tend to transform to adults, in early winter for the former and early spring for the latter, and remain in the host wood for a long period of time. Both species then emerge in large numbers over a very short period of time. This may help explain their relative scarcity in the field, due to a very short adult flight period after a synchronized hatch from the host. Some woods can provide a continuous emergence of beetles for several years. In September of 1990 I collected some dead branches of hackberry (Celtis sp.) from the Carlsbad, New Mexico area. Over a two and a half year span beetles periodically emerged from this host. Species of Cerambicidae reared included Eburia haldemani LeConte, Aethcerinus latecinctus (Horn), Tragidion coquus (Linaeus), Plionoma suturalis (LeConte), Neoclytus caprea (Say), Anelaphus moestus (LeConte), Haplidus laticeps Knull, and Sternidius mimeticus (Casey). At least four species of Buprestidae were reared as well, two of the genus Acmaeodera and two of the genus Chrysobothris. Feeding can still be heard in the branches, indicating more things still to come. None of the branches are over two inches in diameter so the density of larvae is very interesting. Occasional wetting of the wood is necessary to prevent desiccation of the feeding larvae. This is a good example of how a collecting trip to some remote part of the country doesn’t need to end when you drive home. Collecting wood to rear provides species that you may not have encountered or things that are out at a different time of year. The surprises as specimens emerge add to the fun of a tri that may have ended years ago! Data about predators and parasites of wood-borers can be gleaned from rearing as well. Many Cleridae, Cucujidae, and a variety of parasitic Hymenoptera can be obtained from the host woods, and host-parasite associations can be studied. There is the occasional misfortune of the parasite being more successful in your rearing cages than you would like and the result is a flood of wasps and few beetles. I once had a mite infestation wipe out a population of P. amoenus in grape vines, killing nearly every adult in its pupal cell. A word of caution here - Check wood for signs of ants before you bring it indoors. Many small species of ant use abandoned burrows of wood-borers as nesting cavities. The potential problems are obvious! When choosing wood to bring indoors a few tips on what to look for might be helpful. The larvae of several species prune branches from the host plant and the adults of a couple of species girdle branches. The clean cut ends of these branches are a good sign of larval activity. Wood cut or killed during spring or summer and left in the field will be the most heavily infested and provide the best rearing materials. Don’t overlook wood that has been dead for a couple of years or more as this will provide different species than freshly killed wood. Even decayed wood is host to many things, especially Lepturinae and Prioninae. Firewood piles provide an excellent source of recently cut, easily handled wood of a variety of kinds. Wood showing signs of previous emergences can still be productive as many species have life cycles of a couple of years or more and many others will continually re-infest their host until it is too decayed to support them. The only real trick to successful rearing is to bring in as large a variety of host species as practical (apartments fill up quickly!) and try woods at various stages of decay from a variety of localities. With a little practice and patience you will certainly be rewarded with many nice additions to your collection and plenty of interesting data about the species you rear. - Bob Androw What's in a Name?Naming insects is like naming cars, or oceans, or lunar craters. Do you name them after yourself, a friend, a relative, imagined or real attributes? Auto monikers can memorialize relatives (Edsel), connote a supposed mechanical personality (Fury, Valiant), social status (Imperial, Marquis), animals (Pantera, Rabbit), birds (Skylark, Eagle), races and raceways (Grand Am, LeMans, Bonneville), of course astronomical objects that move fast or explode (Comet, Nova), even non sequiturs (Vega), a rock (Plymouth), and casual clothing (Blazer). So, with the same sort of rules operating in systematic nomenclature, it should be no surprise to find insect names following similar patterns. There’s the occasional murkiness, perhaps owing to the requirement of the International Code of Zoological Nomenclature that names be latinized. This Mediterranean connection has led to their frequent derivation from Greco-Roman mythological figures and themes. William S. Blatchley, the patron saint of Midwestern coleopterists, evidently appreciated the classical origins of beetle names. He gave English translations of most generic epithets in his famous tract, An Illustrated Descriptive Catalogue of the Coleoptera or Beetles Known to Occur in Indiana (1910). Like automobiles, beetles get labeled with fancied or real attributes by taxonomists (the following examples are taken from Blatchley’s work). Thus, Omophron is a group of streamside "savage-like" ground beetles, Harpalus are "greedy", and Dyschirius have a "bad hand" (unlucky at poker?). Many ground beetles are drab, but Calosoma means "beautiful body". Speed counts here too, as in cars, so Dromius are "runners", Tachys are "swift", Badister are "fast walkers". Bradycellus, however, are "slow footed". We are not surprised that Pasimachus means "all fight". But there’s a couple of incomprehensible names too: how on Earth might Panagaeus be "all-holy"? Maybe I’ll find one this summer and discover the reason. If I could have anticipated my later insect interests I might have done better in grade school Latin: I’ll bet Bill Blatchley didn’t sit in the back row as often as I did. His enthusiasm for beetles and their names jumps from his pages, inspiring me now as we all patiently (?) wait for winter to end. Editor’s Note: Our favorite is the neotropical dynastid, Enema pan. We are hesitant to investigate the origin of this name (Yes it’s a real name!) - Foster Forbes Purrington |