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Corn plants expressing the toxin from Bacillus thuringiensis (Berliner) have proven to be effective in controlling lepidopteran pests such as the European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae). Several Bt toxins are being tested and incorporated into crop genomes, although tests for cross-resistance among different toxins have been limited by a lack of resistant colonies. Four different colonies of O. nubilalis selected with full-length Cry1Ab incorporated into artificial diet developed significant levels of resistance (2.0- to 10-fold) within 10 generations. Additionally, selection with Cry1Ab resulted in decreased susceptibility to a number of other toxins to which the selected colonies were not previously exposed. Significantly, levels of resistance were highest to Cry1Ac with resistance ratios up to 51.0-fold. Low levels (less than five-fold) of cross-resistance were detected with Cry1F. In contrast, Cry9C susceptibility was unaffected by selection with Cry1Ab. These results indicate that the availability of multiple toxins could improve resistance management strategies, provided cross-resistance among toxins is not a factor.

Susceptibility to Cry1Ab and Cry1Ac toxins from Bacillus thuringiensis was determined for 11 populations of neonate European corn borer,Ostrinia nubilalis (Hübner), from the United States and 1 from northern Italy. Corn borer larvae were exposed to artificial diet treated with increasing B. thuringiensis concentrations, and mortality and growth inhibition were evaluated after 7 d. The range of variation in B. thuringiensis susceptibility indicated by growth inhibition was very similar to that indicated by mortality. Although interpopulation variation in susceptibility to both proteins was observed, the magnitude of the differences was small (≤4-fold) and comparable to the variability observed among generations within a particular population (≤3-fold). Additionally, there was no indication that B. thuringiensis susceptibility was influenced by pheromone race, voltine ecotype, or geographic location. These results suggest that the observed susceptibility differences reflect natural variation in B. thuringiensis susceptibility among corn borer populations rather than variation caused by prior exposure to selection pressures. Therefore, European corn borers apparently are susceptible to B. thuringiensis toxins among populations across most of their geographic range.

We have identified resistance mechanisms in the German cockroach, Blattella germanica (L.), for propoxur and chlorpyrifos in strains of cockroaches that display multiresistance to several organophosphate and carbamate insecticides. The resistance mechanisms involve the combined effects of increased oxidative and hydrolytic metabolism and both strains are resistant to chlorpyrifos and propoxur. Experiments designed to test for similarity in metabolic enzymes suggest that, although the mechanisms involve similar processes, the enzymes responsible for insecticide detoxification are different in the two strains. Both resistant strains exhibited enhanced activity toward a-naphtholic esters relative to a standard susceptible strain; however, analysis of the progeny from resistant × susceptible crosses suggests that this general esterase activity is inherited differently than propoxur or chlorpyrifos resistance. Hybrids of the propoxur-resistant strain displayed the highest activity of all cockroaches tested, in contrast to hybrids of the chlorpyrifos-resistant strain, which were similar to the susceptible strain. Native gel electrophoresis of cytosolic preparations provided further evidence for differences in the pattern of hydrolytic enzymes and inheritance of resistance in the two strains. Analysis of components of the cytochrome P450-dependent monooxygenase system and activities toward model substrates indicate that the two resistance mechanisms also involve different oxidative processes. The propoxur-resistant strain displayed significantly higher levels of total cytochrome P450, but no other components were correlated with resistance. In contrast with the chlopyrifos-resistant strain, which was similar to the susceptible strain in all parameters measured, activity toward model substrates was higher in the propoxurresistant strain than in any of the other strains and hybrids tested. Progeny of the susceptible and propoxur resistant crosses displayed similar levels of monooxygenase components to the susceptible strain, indicating that increased oxidative metabolism is a recessive trait in the Baygon-R strain.

Results of studies to determine the mechanism of resistance in a parathion resistant strain of green bugs, Schizaphis graminum (Rondani), indicated that the resistance mechanism is a combination of metabolic detoxification and target site insensitivity. In vivo metabolism experiments confirmed involvement of metabolic detoxification based on decreased rates of paraoxon formation in the resistant strain. Reduced paraoxon formation is either the result of lower activity of cytochrome P450-dependent oxidases that catalyze desulfuration of parathion, or increased hydrolytic metabolism of paraoxon. Resistance was also associated with a 2.5-fold decrease in sensitivity of acetylcholinesterase to paraoxon inhibition; therefore, we conclude that target site insensitivity and metabolic detoxification interact to confer overall resistance levels.

The toxicity of, synergism of, and resistance to insecticides in four strains of German cockroach, Blattella germanica (L.), were investigated. Toxicity of nine insecticides by topical application to the susceptible strain varied ’2,000-fold, with deltamethrin (LD50, = 0.004 μg per cockroach) and malathion (LD50 = 8.4 Ilg per cockroach) being the most and least toxic, respectively. Resistance to pyrethrins (9.5-fold) in the Kenly strain was unaffected by the synergists piperonyl butoxide (PBO) or S, S, S-tributylphosphorotrithioate (DEF), suggesting that metabolism is not involved in this case. Malathion resistance in the Rutgers strain was suppressible with PBO, implicating oxidative metabolism as a resistance mechanism. The Ectiban-R strain was resistant to all the pyrethroids tested, and cypermethrin resistance was not suppressible with PBO or DEF. These findings support results of previous studies that indicated this strain has a kdr-Like mechanism. Bendiocarb resistance in both the Kenly and Rutgers strains was partially suppressed by either PBO or DEF, suggesting that oxidative and hydrolytic metabolism are involved in the resistance. Trends between the effects of the synergists on the susceptible versus resistant strains are discussed.

Topical bioassays were conducted in 1995 to estimate the susceptibility of adult western corn rootworm, Diabrotica virgifera virgifera LeConte, populations from Nebraska to technical grade methyl parathion, carbaryl, and bifenthrin. Significant differences in susceptibility occurred among populations for each insecticide. The largest relative differences in LD50 values between the most tolerant and susceptible field populations were 16.4- and 9.4-fold for methyl parathion and carbaryl, respectively. The Fl colonies also exhibited significant differences in susceptibility to methyl parathion and carbaryl indicating that susceptibility traits are heritable. The response to bifenthrin (up to 4-fold difference in LD50 values) was more homogeneous across populations than the response to the other 2 compounds. Populations with the largest LD50values were located in 2 areas where adult management programs using carbamate and organophosphate insecticides have been extensively applied and control failures have been commonly reported. Results strongly suggest that corn rootworm management practices have selected for significant levels of resistance to methyl parathion, carbaryl, or both in certain areas of Nebraska.

A susceptible and two parathion-resistant strains of the green bug, Schizaphis Graminum (Rondani), exhibit three different patterns of general esterase isozymes in native polyacrylamide electrophoresis gels. Characterization of general esterase activity using a-naphtholic esters as model substrates indicated that the three strains differed in isozyme composition. The type-II strain, which had the highest level of resistance, exhibited the highest levels of general esterase activity under all assay conditions, and the type-I strain had consistently higher levels than the susceptible strain. In all three strains, these esterases were more active toward a-naphtholic esters with side chains of six or fewer carbon atoms. a-Naphthyl propionate was the optimal substrate for both susceptible and type-I strains, and a-naphthyl butyrate for type II. Over 90% of esterase activity was localized in the cytosolic fraction of type-II greenbugs. In susceptible and type-I greenbugs, the activity was distributed equally between the cytosolic and microsomal fractions. Differences in kinetic properties of the general esterases from the three strains also were evident, further indicating differences in isozyme composition. Although the three strains differed in properties of the general esterase activities, the differences do not provide sufficient discrimination to distinguish reliably among the three strains using single aphid activity measurements.

Baseline carbaryl susceptibility and potential resistance mechanisms were identified in U.S. populations of western corn rootworm, Diabrotica virgifera virgifera LeConte, using lethal concentration, diagnostic concentration, and synergism bioassays. Twenty-two adult rootworm populations were examined from the states of Indiana, Illinois, Iowa, Kansas, Nebraska, Ohio, Pennsylvania, South Dakota, Texas, and Virginia. Lethal concentration bioassays, conducted within carbaryl-coated glass vials on 12 populations, identified resistance in only 2 Nebraska populations. A diagnostic concentration of carbaryl was subsequently identified which caused 100 and 40% mortality in standard susceptible and known resistant populations, respectively. In diagnostic concentration bioassays on all 22 populations, substantial decreases in mortality were observed only in 3 populations from outside of Nebraska. Synergism bioassays on standard susceptible and resistant Nebraska populations indicated significant reductions in resistance levels with inhibitors of both cytochrome P450 monooxygenases and esterases, suggesting an involvement in resistance by both these classes of detoxification enzymes. Results are discussed with respect to the validation of diagnostic concentration bioassays as a resistance monitoring tool for existing corn rootworm areawide management programs, and the potential roles of cytochromes P450 and esterases in carbaryl resistance.

Insecticide susceptibility of field populations of stable flies, Stomoxys calcitrans (L.), was assayed using 3 exposure techniques: treated filter papers, treated glass petri dishes, and topical applications. Both topical applications and residual exposure to treated glass surfaces were suitable for testing susceptibility of stable flies to permethrin, stirofos, or methoxychlor. Residues on filter papers yielded inconsistent results with stirofos and methoxychlor. Significant concentration−mortality regression lines were generated with pennethrin residues on filter papers, but ≈1,000 times more insecticide was required to produce a toxic response when compared with permethrin residues on glass. Because of higher variability in response and the greater amount of insecticide required, residues on filter papers do not appear appropriate to test insecticide susceptibility in stable flies. Paired comparisons of field (F) and susceptible (S) stable flies resulted in field to susceptible ratios significantly >1.0 only when the flies were treated topically, which suggests that topical application is more sensitive than residues on glass for the insecticides tested. Topical treatment with permethrin resulted in one FS(LD90) of 1.8-fold. Topical treatment with methoxychlor resulted in one FS(LD90) of 3.4-fold. However, the magnitude of these ratios is not larger than the significant differences observed within the susceptible laboratory colony from one generation to another. Intense exposure to insecticides is not known to have occurred in these field populations, indicating that the observed differences are the result of natural variation among stable fly populations and unrelated to prior selection with insecticides.

Sixty commercial pesticide formulations were tested in the laboratory for toxicity to eggs, larvae, and adults of the green lacewing, Chrysopa carnea Stephens, at dosages similar to those used in orchards. The eggs were treated directly with the sprays. The larvae (fed a special diet to restrict cannibalism) and adults were tested on day-old residues. The pesticides are rated as having high, medium, low, or 0 toxicity. The eggs were highly susceptible to oil. Their hatch was delayed by parathion. Other materials had little effect on the eggs. Larvae and adults were killed by the residues of most of the organic phosphates and chlorinated hydrocarbons tested, but a few materials of each of these groups showed singularly low toxicity to the larvae. Day-old residues of some contact insecticides tested were harmless to all stages of this predator. Most of the acaricides, fungicides, and stomach poisons tested were not toxic. Toxaphene delayed larval growth. Several materials offer possibilities for use in integrated control programs where protection of the green lacewing is desired, and 2 materials extraordinarily toxic to it may be useful for insecticidal cheeks on this predator’s efficiency.

The effects of the residues of 62 commercial pesticides upon the predatory phytoseiid mite, Amblyseius hibisci (Chant), were examined in the laboratory to obtain information on how this species may be protected in integrated chemical and biological control programs, and how the effectiveness of this predator May be measurted with pesticidal check procedures, i.e. by the host increase arising from the predator's elimination by pesticides. Methods of handling, feeding, and testing the adult mites are described. Laboratory test results on adult A. hibisci are presented along with a list of published laboratory and field reports on the effects of the same toxicants upon other species of phytoseiids. Almost all the organic phosphate and carbamate insecticides tested were moderately to highly toxic. Considerable tolerance was shown by the adults to 2 of the chlorinated hydrocarbons, 4 of the acaricides, 3 of the stomach poisons, and 4 of the fungicides tested. Conflicting reports of pesticide effects upon other phytoseiids emphasize the variability in response to be expected with different species of this group. Subjects discussed are pesticide specificity to phytoseiids, characterization of pesticides causing destruction of phytoseiids, potential integrated control or pesticidal check materials, and apparent associations between phytoseiid destruction and the increase of phytophagous mites.

Sixty-one pesticides were tested in the laboratory against 5 parasitic hymenopterans and 6 predatory coccinellids, the data to serve as guides for selecting the best materials for destroying pests without undue harm to natural enemies. Test species were exposed in replicated tests to day-old residues of the pesticides under standardized conditions of dosage, temperature, and humidity. The single dosages applied were those most commonly used upon orchard crops. A table presents toxicity levels for each material and natural enemy species in conjunction with a rating of the persistence of each pesticide’s toxic residue. The data suggest that the effect of each pesticide upon most kinds of adult parasitic Hymenoptera may be anticipated with a high degree of reliability while the effect upon predatory coccinellids is much less predictable. The materials are discussed with respect to their specificity and the probable impact that their field usage might have upon parasitic Hymenoptera and predaceous Coccinellidae.

Studies were conducted on the control of the western peach tree borer, Sanninoidea exitiosa graefi (Hy. Edw.), in apricots with both soil fumigants and trunk sprays from 1955 through 1958. Results were first evaluated by caging the trees to trap emerging adults, later by counting empty cocoons or papal eases, and finally by strike counts in the early fall. The last-mentioned method was found to he the most practical. In the soil fumigation trials paradichlorobenzene, propylene dichloride, and tetrachloroethane gave good results. Ethylene dichloride was the least effective in these trials. Tetrachloro- chance although it killed borers, was extremely phytotoxic. Trunk treatments were made during the 1957 and 1958 sea- Soon. In 1957 Thiodan® (6,7,8,9,10-hexachloro-1,5,5a,6,9.9a,hexah, Hydro-6,9-methaono-2,4,3-benzodioxnthiepin-3-oxide) a no endrin Applied three times at monthly intervals gave good control. DDT was also effective, and three was little difference, between treatments at monthly or bimonthly intervals. The addition of a sticker to DDT did not improve its performance. Whitewash, applied to trees in late May, did not prevent borer attack. In 1958, Thiodan and endrin gave excellent control whether treated four times at monthly intervals or twice at bimonthly intervals. Guthion® (O,O-dimethly , s-(4-oxo-1,2,3-henz- triazine-3-methyl) phosphorodithioate) was effective at monthly intervals hut less so at bimonthly intervals, DDT was not so good as the above compounds, hut gave commercial control when applied four times at monthly intervals. A single treatment of dieldrin in June did not provide satisfactory control.

Orchard trials with new spray chemicals for thc control of the rosy apple aphid (Anuraphis roseus Baker) and the apple aphid (Aphis pomi De Geer) were conducted on Yellow Newtown and Red Delicious apples during 1957 and 1958. Delayed dormant sprays against eggs of the rosy apple aphid demonstrated that ethion-oil, Phostex®,(a mixture of bis (dialkyloxyphosphinothioyl) disulfides)-oil, and Trithion® (S-(p-chlorophenylthio) methyl O,O-diethyl phosphorodithioate)-oil gave control equal to the standard oil-dinitro sprays, and did not injure thc cover crop. Foilage treatments for the rosy apple aphid in 1957 and 1958 indicated that systemic compounds, demeton, Thimet® (O,O-diethyl S-(ethylthio) methyl phosphorodithioate), dimethoate Am. Cyanamid 18706® (O,O- dimethyl S(N-ethyl carbamoylmethyl) phosphorodithioate), and Di-syston® (O,O-diethyl S-2-(ethylthio)-ethyl phosphorodithioate) would provide good control. Diazinon® (O,O-diethyl O- (2-isopropyl-4-methyl-6-pyrimidinyl) phosphorothiate) was the only nonsystemic material to provide control of the rosy apple aphid. Guthion® (O,O-dimethyl S-( 4-oxo-3H-1,2,S-benzotriazine- 3-methyl) phosphorodithioate), Sevin® (N-methyl-1-naththyl carbamate), Rohm-Haas C-140® (dimethyl carbamate of 2- dimethylaminomethylphenol hydrochloride), ethion, and Thiodan® (6,7,8,9, 10,10-hcxachloro-1, 5, 5a, 6,9,9a-hexahydro-6, 9- methano-2,4,S-benzodioxathiepin-3-oxide) were not effective. Summer treatments for control of apple aphid were applied during the 1957and 1958 seasons. Apple aphid does not become a problem until June, and repeated re infestation makes control difficult. The systemic compounds Thimet, Di-syston, Am. Cyanamid 18706, and dimethoate provided the best control. Nonsystemic compounds, although reducing populations following thc application, did not prevent re infestation and rapid buildup.