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The ability of Nabis alternatus Parshley to reduce tobacco budworm, Heliothis virescens (F.), populations was studied in the laboratory, greenhouse and field. Tests were conducted at different temperatures and with different larval instars of tobacco budworm to determine their effects on predatory efficiency. Both immature and adult N. alternatus consumed more first-instars than of either second- or third-instars, or of the egg stage. Temperature significantly affected the predatory capability of N. alternatus. All instars and the adult exhibited a higher rate of consumption at 30°C than at temperatures of 20, 25 and 35°C; adults consumed more tobacco budworm larvae and eggs at all temperatures than did any of the nymphal instars. There were no differences in survival of the different N. alternatus stages at the different temperatures but the average number of days required to complete each instar was affected. Each increase in the predator-to-prey ratio resulted in a reduced survival of the tobacco budworm population. Release rates of 2500, 3750 and 5000 adults per acre resulted in mortalities of 55, 77, and 87%, respectively. Both adult and third-instar N. alternatus exhibited the higher searching and consumptive capacities at different ratios of first-, second-, and third-instar tobacco budworm infestations. All N. alternatus fed more at the 1:4 (predator/prey) ratio than at ratios of 1:1, 1:2, or 1:3. Longevity of adult N. alternatus varied when provided with food substances of sugar solution, green bean, no food or cotton plants at the different temperatures. Survival was greatest when provided with sugar solution over any of the other substrates, and when held at cooler temperatures. Compatibility of N. alternatus with other controls was studied under both laboratory and field conditions. Average longevity in combination with treatments of Elcarᴿ, Bacillus thuringiensis, or fenvalerate was 6.7, 5.9, and 1.3 days, respectively. Compatibility with the biological insecticides was very good and the combinations reduced first-instar tobacco budworm infestations more than did either alone.

Efficacy of Bacillus thuringiensis Berliner against the first three larval instars of Heliothis virescens (F.) was studied under greenhouse and field conditions. The primary objective of these studies was to determine the susceptibility of the tobacco budworm to Dipel, a commercial preparation of Bacillus thuringiensis. Both greenhouse and field studies showed that first-instar larvae were more susceptible to all dosage levels of Dipel tested (0.125, 0.25, 0.5, and 1.0 1b/A). The higher rates of 0.5 and 1.0 1b/A gave better control and remained effective for longer periods against the first-, second- and third-larval instars than did the lower rates of 0.125 and 0.25 1b/A. The efficacy of all Dipel rates decreased significantly with each subsequent post-application-date bioassay, and only the higher dosages of 0.5 and 1.0 1b/A remained effective at the three-day residue period in the field studies. The addition of a feeding stimulant, Coax, at 0.25 1b/A, to all Dipel treatments resulted in a significant increase in larval mortality of all instars tested. Dipel plus Coax exhibited longer residual activity than did Dipel alone, indicating that Coax may protect the spores and toxin from degradation by the direct sunlight. When second-instar tobacco budworm larvae were allowed to feed on Dipel-treated terminals for 6, 18 or 30 hours and then transferred to untreated diet, they showed a great capacity to recover from the effect of the toxin. However, as the Dipel rate or exposure time was increased, the ability of larvae to recover was decreased. Dipel did have an effect on the biological activity of treatment-surviving larvae. Larval and pupal development was delayed, pupal weight was decreased, and female fecundity was reduced. In all cases the changes were proportional with the Dipel rate and with the length of exposure. No apparent effect was shown relative to adult longevity or egg viability for those surviving Dipel treatments as larvae. When Dipel was applied directly on tobacco budworm eggs, it had no effect on egg hatch but did significantly affect survival of newly-emerged larvae, indicating the larvae consumed a lethal dose of the toxin during eclosion. The compatibility of Dipel in combination with Geocoris punctipes (Say) against first-instar larvae of Heliothis virescens was also studied under greenhouse and field conditions. Results of these studies indicated the possibility of utilizing the two biological agents to suppress tobacco budworm populations in the field. A minimum density of one Geocoris nymph per 4 row feet is required, plus an effective field rate of Dipel. When adult tobacco budworms were fed on Dipel at 32000 IU/ml, their longevity and fecundity were significantly reduced. An adult feeding stimulant is needed to lure the adults to a Dipel source.

A strategy for the discovery of new insect growth regulators from arid lands plants was developed. Plant genera with a history of toxicity, medicinal use, or incorporation in native american cultures were selected. Forty-five species from twenty-one families were collected, extracted, and tested for biological activity on the large milkweed bug, Oncopeltus fasciatus. Eight extracts were toxic and the extract of Nama hispidum (Hydrophyllaceae) caused nymphs to undergo precocious metamorphosis to an adult. The active component of N. hispidum was precocene II (6,7-dimethoxy-2,2-dimethyl chromene). Nine Nama species, representing four of the five sections in the genus were gathered from Hawaii, California, Nevada, Arizona, New Mexico, and the Dominican Republic. In addition to the insect anti-hormone, precocene II (PII), present in N. hispidum, N. rothrockii contained at least two different insect juvenile hormone mimics, and N. sandwicense contained insect anti-hormone and insect juvenile hormone mimics. Fifth instar larvae of Heliothis zea were used as model insects to distinguish between post-ingestive intoxication and feeding deterrency during exposure to PII. Larvae fed artificial diet with PII were deterred from eating, and had retarded weight gain, growth, and development. Insects grown on diet with PII consumed less food, could not digest the food, or convert ingested food to body mass. in vivo radiotracer studies with the nutrient, ¹⁴C linoleic acid, show a lower rate of transport and incorporation of radioactivity into fat body tissue. A change in the midgut epithelial cells from PII resulted in reduced transport efficiency and retarded larval growth and development. Scanning electron microscopy of the midgut epithelia indicated that cytotoxic damage is induced by PII. Observed changes in the midgut epithelial cells are consistent with a destructive alkylation of cell structures by PII.