William L Hilsenhoff

Diversity and Classification of Insects and Collembola

Publisher Summary This chapter describes classification, anatomy, morphology, physiology, reproduction, life history, phylogeny, evolution, ecology, and taxonomy of orders and families in which one or more life stages are truly aquatic and adapted for survival under or on the water surface. It also briefly mentions another arthropod group, the semiaquatic springtails (class Entognatha, order Collembola). A total of 10 orders of insects contain aquatic species. Five of them (Ephemeroptera, Odonata, Plecoptera, Trichoptera, and Megaloptera) are aquatic orders in which almost all species have aquatic larvae. The remaining five orders (Heteroptera, Coleoptera, Diptera, Lepidoptera, and Neuroptera) are partially aquatic orders in which most species are terrestrial. However, these orders contain species or entire families that have one or more life stages adapted for living in an aquatic environment. Three aquatic orders (Ephemeroptera, Odonata, and Plecoptera) have a hemimetabolous life cycle, which includes three developmental stages: egg, larva, and adult. The other two aquatic orders (Trichoptera and Megaloptera) have a holometabolous life cycle, which includes four developmental stages: egg, larva, pupa, and adult. Four of the five partially aquatic orders (Coleoptera, Diptera, Lepidoptera, and Neuroptera) also have holometabolous life cycles. The fifth order, Heteroptera (Hemiptera), has a paurometabolous life cycle, which includes three developmental stages: egg, larva, and adult.

A virus disease in Chironomus plumosus

Abstract A previously undescribed virus disease has been discovered in larvae of Chironomus plumosus sampled from Lake Pepin, Wisconsin. The disease is characterized by a marked hypertrophy of the fat body and by the presence of large DNA-containing inclusions in the cytoplasm of this tissue. Preliminary ecological studies indicate that at least 40% of fourth-instar larvae may be infected in some years. Electron-microscopic studies of infected fat body reveal extensive areas of viral proliferation in the cytoplasm. The virus particles measure about 145 mμ in diameter, and are similar in morphology to the iridescent insect viruses. They differ in having bundles of fine fibrils in association with the outer shell of the virus. These may prevent the formation of microcrystalline arrays of virus particles, explaining a lack of iridescence in diseased chironomid larvae.

Review of first-instar larvae of Colymbetini (Coleoptera: Dytiscidae), with a key to genera and phylogenetic analysis

The first-instar larva of Meladema coriacea Laporte, 1835 is redescribed, and that of Neostutopterus hornii (Crotch, 1873) is described for the first time. A generic key to first-instar larvae of Colymbetini is presented, but it does not include the monobasic New World genera Bunites Spangler and Hoperius Fall, whose young larvae are unknown. Polarity is determined for a set of 12 characters of first-instar larvae, and the distribution of character states among genera is used to reconstruct phylogeny. It suggests that Meladema Laporte and Neoscutopterus J. Balfour-Browne together form the most derived lineage of the Colymbetini, whereas Colymbetes Clairville is the least derived genus.

The Effect of Toxaphene on the Benthos in a Thermally-Stratified Lake

Abstract Chaoborus larvae were the only profundal benthic organisms that were adversely affected by treatment of a dimictic lake with toxaphene to eradicate undesirable fish. The larvae were eliminated, and had not become reestablished 2 years after treatment. Subesquent to removal of the fish, an extremely large population of Chironomus larvae appeared, and when the lake was restocked with 7 species of fish, the population dropped to its former level. More than a year after treatment, a substantial population of Procladius larvae appeared, probably resulting from the removal of carp and the consequent reduction of turbidity, increased growth of rooted aquatic vegetation, and restoration of higher dissolved oxygen levels. The temporary absence of fish also favored an increase in the physid snail population.

Infection of Chironomus plumosus (Diptera: Chironomidae) by a Microsporidian (Thelohania sp.) in Lake Winnebago, Wisconsin☆

Abstract A new species of Microsporidia, in the genus Thelohania, was found infecting fourth-instar larvae of Chironomus plumosus in Lake Winnebago, Wisconsin, causing 61% mortality over a 29-day period and inhibiting the pupation and emergence of adult flies. Larvae became infected before the final instar, but the large masses of spores were observed only in fourth-instar larvae in which the fat bodies were well developed. Fourth-instar larvae could not be infected in the laboratory, although 97% of first-instar larvae exposed to Thelohania sp. spores became infected. The incidence of parasitism of fourth-instar larvae in Lake Winnebago often varied from one area of the lake to another, and varied greatly from one generation to the next.