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Behavioral responses reported for spider mites encountering pyrethroid in secticideson treated plant surfaces have included increased dispersal and cessation of feeding. In our laboratory study, pyrethroid insecticides were applied directly to Banks grass mite, Oligonychus pratensis (Banks), and two spotted spider mite, Tetranychus urticae (Koch), that were then released onto untreated maize, Zea mays L., plants. Initially, a greater proportion of chemically treated mites dispersed compared with untreated mites or those treated with water. Vertical distributions of the two species were similar except after the permethrin treatment. Permethrin inhibited Banks grass mite upward dispersal compared with fenvalerate, water treatments, and controls, whereas two spotted spider mite upward dispersal was not inhibited.

Populations of field-collected Blattella germanica (L.) were placed in one chamber of a modified Ebeling choice box and subjected to selected environmental influences. Relative importance of these influences was determined through analysis of differences in sticky-trap catches which reflected exploratory behavior. Daily trap-catch data were associated with each variable tested. The number of cockroaches caught was found to increase with environmental familiarity, increased temperature, increased number of holes between chambers (especially those located at the bottom of the partition), and food deprivation. Decreased catches resulted from increased cockroach density and fecal contamination.

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.

We developed a rating system to predict the mortality of Diabrotica undecimpunctata howardi Barber larvae used to bioassay soil insecticides. Larvae were categorized, following 48 h exposure to insecticide-treated soil, as living, dead, or in one of five intermediate categories based on movement when exposed to bright light. The eventual mortality of larvae within a rating category was determined by returning the larvae to the treated soil for an additional 5 days and establishing the probability of mortality corresponding to each category. Percentage of dead larvae in the five behavioral rating categories was independent of the insecticide used. Compared to the bioassay method in which the test organisms are considered either alive or dead, the rating system was more consistent and more precise with respect to the assumptions underlying conventional parametric statistics. The rating-system approach is a sensitive and rapid bioassay technique that might be adapted to other test organisms and situations where the subject is under continuous exposure to the toxin being tested.

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.

German cockroach nymphs ( Blattella germanica (L.)), large milkweed bug nymphs ( Oncopeltus fasciatus (Dall.)) and adult spotted alfalfa aphids ( Therioaphis maculata (Buckton)) were exposed daily for short periods to several areas of the visible spectrum. Daily exposures of cockroaches to light indicated that the longer wave lengths of light may interfere with normal growth. As the daily exposure time was increased, the life span and the mean weights decreased. Daily exposure of the milkweed bugs to the longer wave lengths resulted in an increased maturation period, decreased adult weights, and fewer nymphs reaching the adult stage. Tests with the spotted alfalfa aphid indicated that short daily exposures to the longer wave lengths of light resulted in the birth of fewer nymphs over a period of several months experimentation. Consideration was given to the mechanism responsible for such growth inhibition.

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.

An inert diatomaceous earth of Arizona origin trade named Perma Guard was evaluated as a grain protectant, insecticidal and pathological properties being studied. Dosage-mortality curves are presented for eight test species confined in wheat dusted with Perma Guard at the rate of 2 to 7 pounds per ton, Ranking in order of decreasing susceptibility these species were: flat grain beetle, Cryptolestes pusillus (Schanherr); rice weevil, Sitophilus oryzae (L.); granary weevil, Sitophilus granarius (L.); lesser grain borer, Rhyzopertha dominica (F.); saw-toothed grain beetle, Oryzaephilus surinamensis (L.); dermestid larva, Trogoderma parabile Beal; red flour beetle, Tribolium castaneum (Herbst); and confused flour beetle, T. confusum Jacquelin du Val. Only the flat grain beetle mortality attained standards of commercial kill during the two weeks' exposure period at the commercially recommended dosage (4 pounds per ton) or below. Mortality exceeded 95% at 5 and 6 pounds per ton for this species. At the peak dosages used, the mortality of the remaining species did not approach the criterion for commercial kill, The results indicate that of the two moisture levels (12% and 14%) of wheat used in this study, the lower level contributed to mortality in both weevil species, the lesser grain borer and the saw-toothed grain beetle. The dust was directly applied to five test species. Significant differences in losses in weight were observed between test and control groups for the lesser grain borer, the confused flour beetle and the red flour beetle. Overall differences in losses in weight between test and control lots of rice and granary weevils were not significant. A drastic difference between test and control first-day mortality in the rice weevil may be indicative of an unknown lethal factor in the dust. The significant differences in loss in weight were ascribed to the dust's abrasive action on the water barrier portion of the epicuticle. The toxicology of this diatomaceous dust was studied. Dissections, epicuticular staining. and histological sectioning showed little that could be construed ns epicuticular damage.

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.

The relative resistance of the western corn rootworm, Diabrotica rirgifera LeConte to aldrin and diazinon was determined for adults collected from 18 sites in Nebraska and from several sites in adjacent States. The LD50 values in micrograms/gram of insect were determined by topical application for all collection sites. The results indicate a wide range in susceptibility for insects collected in Nebraska. By comparison with the LD60 values of Nebraska-collected insects, it would appear that control problems might occur ill some of the surrounding States in the near future.

Forty-eight species of cultivated and wild flowering plants in Nebraska were assayed for juvenile hormone (JH) activity. Except for a few plant species, extracts were made of flower heads. Extracts were assayed using pupae of the yellow mealworm, Tenebrio molitor L., as test indicators of JH activity. Examination of over 900 T. molitor adults, treated as pupae, revealed limited evidence of juvenilization. Vestigial urogomphi were present on some adults previously treated as pupae with extracts of 5 plant species. Bioassay of Nepeta cataria (Tourn.) Reichenb, extracts revealed 1 pupal-adult intermediate.

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.

During the last three to four decades, numerous insect species have been exposed to a series of new and more toxic insecticides. After many years of exposure to certain insecticides in the field, assays of some insect populations now show decreased susceptibility to those toxicants. The response of insects to the continued exposure to various insecticides has resulted in a phenomenon well known to all entomologists as insecticide “resistance.” Resistance, according to Crow (1957), designates a genetic change which is a response to pesticide selection.

Reproduction of the red flour beetle, Tribolium castaneum (Herbst), was lower on whole grain than has been reported on milled grain in earlier studies. Generally, fecundity increased with increasing temperature (20-32°C) and moisture (10-16%). However, interaction of adult survival and fecundity caused net reproduction to peak at 27°C and 16% moisture. This resulted from greater adult survival with increasing moisture, but decreasing survival with increasing temperature.

Adults of Diabrolica virgifera LeConte were placed in choice boxes whose tops consisted of filters of six different wavelengths ranging from ultraviolet to red. Observations to determine the most attractive wavelengths, made five times daily, indicated that wavelengths in the yellow spectral region were significantly more attractive than those in the red region; additionally, red was more attractive than other wavelengths tested. The use of colored traps for assessing field populations of adult western corn rootworms is indicated.

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.