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Secretory-type epithelial cells of the adult female western corn rootworm, Diabrotica virgifera LeConte (Chrysomelidae), apparently responsible for releasing the sex pheromone, are composed of 2 groups of cells. One group is columnar, arranged in a “U” shape, and located dorsally between tergites 7 and 8; the cells of the 2nd group are cuboidal and located ventrally between sternites 7 and 8. Individual cuticular pore openings occur on the 7th abdominal segment and correlate spatially with the epithelial secretory cells.

The effects of topically-applied sublethal doses of carbofuran and carbaryl on oviposition and longevity of Diabrotica virgifera LeConte females were studied. At application rates representing very small percentages of their respective LD50 values, females treated with either insecticide oviposited significantly more and lived significantly longer than did control females. Carbofuran enhanced these phenomena more consistently than did carbaryl. No explanations are suggested as to why the carbamate insecticides tested stimulated oviposition and extended longevity.

Aldrin was recommended and used to control the western corn rootworm (Diabrotica virgifera LeConte) (WCR) in Nebraska from 1952 to 1961. During that period, LD50 values for adult WCR tested against aldrin were determined for 19 collection sites in Nebraska. Mean 24 h LD50 values for these sites decreased from 1,539 μg/g in 1962 to 355 μg/g for 1981. A correlation existed between the amount of aldrin used for soil treatments and the aldrin and dieldrin residues, with decreasing LD50 values for the WCR over the observation period.

Scanning electron micrographs and serial longitudinal and cross sections of the western corn rootworm, Diabrotica virgifera LeConte , antennae revealed that the antennal structure of males and females was similar. However, the longer ♂ antennae have more sensilla and possess 6 types of sensilla on the terminal antennal segment not found on the terminal segment of ♀ antennae; the ultimate antennal segment of the female possesses 4 sensillar types not found on the comparable antennal segment of the male.

Because it is difficult and time consuming to collect activity data for small insects visually, a recording system using a cage, power source, amplifier, and event recorder was devised to record locomotor activity. The system functions when the test insect makes contact between 2 electrodes placed in the test cage. The system was used to record locomotor activity of Diabrotica virgifera LeConte, Oncopeltus fasciatus (Dallas), and Periplaneta Americana (L.) with different degrees of success, depending upon the conductance (or resistance) of the test insect. Circuit diagrams and operating procedures are presented.

Adults of Diabrotica virgifera LeConte were collected annually from 1963 through 1972 from 18 specific sites in Nebraska and treated with a series of concentrations of diaziuon and phorate to determine annual median lethal dose values. Dosage-mortality curves or regression lines were statistically determined from the annual median lethal dose data. Although the median lethal dose values for both insecticides increased from 1963 to 1972, neither regression line is significant. However, the median lethal dose data for diazinon significantly fit a quadratic curve, indicating possible reversion in susceptibility to diazinon. Predictions of imminent resistance in the field based on the slopes of the regression lines would be speculative.

Approximately 12,000 female Diabrotica virgifera LeConte were extracted with hexane. Part of the resulting extract (oil) was column chromatographed to obtain various ether/hexane fractions. Crude and ether/hexane fractious were bioassayed in the laboratory and in the field. In the laboratory, the 5% ether/hexane fraction was the most attractive; in the field, acetone extracts of the crude hexane extract showed that 500 or more female equivalents were necessary to attract more than 10 males per trap during the testing period.

The sequence of mating behavior for virgin western corn rootworms, Diabrotica virgifera LeConte, included the following behavioral categories: preliminary courtship and mounting; physical stimulation of the female by the male; and copulation. Various tactile stimuli, including antennal palpitation and stroking activities involving the mesothoracic legs, were performed by the male during the mating process.

Starting in 1963 adults of the western corn rootworm, Diabrotica virgifera Le Conte, were collected annually from 18 sites in Nebraska and treated to determine LD30 levels for diazinon and phorate. Dosage-mortality curves and LD30 values are presented for both insecticides for 1963 through 1967. The LD30 values for both diazinon and phorate have increased significantly since 1963. Control of the western corn rootworm with both insecticides remains effective, but the increasing LD30 values should alert entomologists to possible failures in the field.

Twenty-nine insecticidal compounds were assayed for their toxicity to the western corn rootworm, D. virgifera LeConte. The toxicants included 13 carbamates, 13 organophosphates, and 3 chlorinated hydrocarbons. LD50 values in µg/g are presented for all the compounds tested for the years 1963–68. Seven of the 10 most toxic insecticides were carbamates, and 3 were organophosphates.

Adults of the western corn rootworm. Diabrotica virgifera LeConte, collected from two widely separated areas in Nebraska, were assayed for susceptibility to aldrin, Diazinon® ( O,O -diethyl O -(2-isopropyl-4-methyl-6-pyrimidinyl) phosphorothioate), and heptachlor. Dosage-mortality curves and LD50 values were determined for each insecticide. Results indicated that adults of D. virgifera collected from the central part of the State required about 100 times as much aldrin or heptachlor per insect to produce an LD50in 2 hours as adults collected in eastern Nebraska. LD50 values for Diazinon tested on beetles from the two areas were virtually the same. The reasons for such differential resistance are considered.

A technique to obtain objective mortality data for larvae of the western corn rootworm treated with diazinon, Bux® [ m- (l-ethylpropyl) phenyl methylcarbamate mixture with m- (l-methylbutyl) phenyl methylcarbamate], and phorate is detailed. The use of negative phototactic larval activity following insecticide treatment was more consistant than determining death by observation. For diazinon, the percentage differences in LD50 values between larvae and adults (phototactic technique) for 1974 was 1.04. Differences in LD50 values (observation) between larvae and adults for 1962 and 1969 were 51.6 and 17.0, respectively.

A portable collecting device constructed from a 3-inch mailing tube, a 1-pint ice cream container, and a 1-pint metal funnel using a hand vacuum cleaner powered by a portable generator has been used to collect more than 25,000 adults of the northern corn rootworm, Diabrotica longicornis (Say), the western corn rootworm, Diabrotica virgifera LeConte, and the spotted cucumber beetle, Diabrotica undecimpunctata howardi Barber. The device can be used either to collect insects directly or trap them for transfer to larger cages.

The effects of photoperiod on various biological phenomena in insects are well known. Relationships between photoperiod and behavior, reproduction, adult emergence, metabolism, diapause, and numerous other factors are receiving considerable attention. The reason for such studies is to better explain the response of an insect to its environment as related to light. Because photoperiod has significant effects on various life processes in insects, this study was undertaken to determine what effect photoperiod might play in regulating oviposition in the western corn rootworm, Diabrotica virgifera LeConte.

Adult Diabrotica virgifera LeConte were topically treated with a series of dosages of diazinon at 3-hour intervals throughout a 24-hour photoperiod in 1967 and 1968. Results indicate that the LD50 values vary during a 24-hour period, resulting in a sensitivity rhythm dependent upon time of treatment during the photoperiod. The data indicate the desirability of conducting bioassays during specific time periods of a 24-hour photoperiod.