Different planting and termination dates of Pima S-6 and Upland (Deltapine 90) cotton (Gossypium barbadense L. and hirsutum L. respectively) were tested for their effects on pink bollworm (Pectinophora gossypiella) infestations. Tests were conducted during 1989 and 1990 cotton seasons at the University of Arizona Yuma Valley Agricultural Experiment Station. Planting dates indicated little effect on early season infestations of pink bollworm for either cotton. However. irrigation termination had the greatest effect on late season infestations. In 1989. heat unit (degree day 12.8/30° C. lower and upper thresholds) accumulations were several days earlier than 1990, due to a very warm year. Pheromone trap counts indicated higher populations in 1989 than 1990; however. infestations in the field were similar between the years. Infestations dramatically increased during July through September, indicating that a longer cotton season with actively growing fruit, results in a continued population increase. The termination dates affected the amount of fruiting structures left in the field and thereby affected infestations of overwintering larvae in the field. Termination date had a dramatic effect on the % bolls infested with overwintering larvae and the density of overwintering larvae /m.

Responses of five field -collected populations of the pink bollworm. Pectinophora gossypiella (Saunders). from Arizona and southern California. were compared with those of a standard. susceptible -laboratory strain. Field strains showed less than twofold difference in response to azinphosmethyl at LD₅₀ but had variable levels (1.3- to 18.3-fold) of response to permethrin. Strains from Yuma and Phoenix (Arizona) and Westmoreland (California) had highest levels of resistance to permethrin.

Two newly developed insect growth regulators were tested at two dose levels for control of the sweetpotato whitefly on cotton. The two chemicals showed some promise for control although the dose rate and application schedules were not optimal and plot sizes were too small to show a decrease in cotton stickiness or sugar content due to the treatments. In these tests a chitin synthesis inhibitor was more effective in controlling immature stages than a juvenile hormone mimic.

Trap crops, along with delayed uniform planting and pinhead square treatments, greatly reduced spring populations of overwintered boll weevils, Anthonomus grandis Boheman, in a Laveen. Arizona community -wide 1PM program in 1987. Thirty four trap crops. planted fifteen days ahead of the regular crop. had as many as 39536 damaged plants/ha before insecticide treatments were initiated. Five insecticide applications at 3 day intervals beginning at square initiation were used to destroy weevils before the trap crops were plowed under at the time pinhead square treatments were initiated in regular planted fields. Damaged square infestations were 2 to II times lower throughout the season in 1987 compared to 1986 while average lint yields per ha increased from a low of 941 kg in 1985 to 1345 kg in 1986 and 1506 kg in 1987.

Pink bollworm (PBW), Pectinophora gossypiella (Saunders) infestations in Deltapine 90, Gossypium hirsutum L., and Pirna S-6, G. barbadense L., cotton bolls were initiated at about the same time during the cotton growing season. Male moth trap catches in gossyplure-baited Delta traps followed similar trends in both cottons throughout the season, but tended to be higher in Pima S-6 cotton than in Deltapine 90 cotton late in the season. Late crop termination (last irrigation 26 September) as practiced in Pima cotton production vs. earlier crop termination (last irrigation I September) as practiced in upland cotton production resulted in higher numbers of late- season immature green bolls, higher numbers of PBW larvae per boll and higher populations of diapause larvae at harvest time in Pima than occurred in the upland cotton cultivar. PBW seed damage was lower in the Deltapine 90 cultivar than in the Pima S-6 cotton cultivar. Deltapine 90 lint yield was higher than Pima S-6 lint yield.

Plant growth regulators (PGR's) [thidiazuron (Dropp®) N-phenyl-N' -1,2,3-thiadiazol -5 ylurea, 50% wettable powder, Nor-Am Agricultural Products, Inc., Naperville, IL, and ethephon (Prep®) a- chloroethyl phosphonic acid Rhone - Poulenc Ag Co., Research Triangle Park NC] were applied to reduce late- season fruiting forms as a source of host material for developing overwintering PBW populations. Combinations of ethephon and thidiazuron or thidiazuron alone were more effective than ethephon alone for reducing late -season immature green bolls. None of the PGR's alone or in combination affected yields. Highest rates of defoliation occurred after applications of thidiazuron. The data suggest that temperature thresholds for highest plant growth regulator activity occur.

Populations of pink bollworm. Pectinophora gossypiella (Saunders), from Yuma, Casa Grande, Marana and Safford were compared with that of a susceptible laboratory (USDA) strain relative to their susceptibility to permethrin. A limited comparison was made with azinphosmethyl. All field strains were significantly more tolerant to permethrin than was the USDA susceptible strain. A comparison of the USDA and Yuma strains using azinphosmethyl indicated no difference in susceptibility between the laboratory and field strains.

Rearing of two field strains (Maratha, Yuma) of pink bollworm. Pectinophora gossypiella (Saunders). from Arizona under conditions free of insecticides resulted in reversion of resistance (in adults) in four and five generations. respectively. to levels close to that found in the susceptible laboratory strain. Permethrin resistance in these field strains is unstable and is apparently in its early phase of development. Results suggest that monitoring of pink bollworm resistance in field strains reared in the laboratory should be performed in the F₁ generation. Subsequent selection studies were performed on both larval and adult stages to investigate the capacity of the pink bollworm to develop resistance in both life stages. Fourteen generations of selection of larvae and adults with azinphosmethyl produced 1.9- and 1.6-fold tolerance. respectively. in the adult stage. Sixteen generations of larval selection with permethrin generated 9.7-fold resistance in adults. while 14 generations of adult selection produced 8.8-fold resistance in adults. Azinphosmethyl evidently possesses a low degree of selectivity for development of resistance in pink bollworm adults. Selection of larvae with both azinphosmethyl and permethrin seemed to generate higher levels of tolerance in larvae than in adults.

A laboratory selected permethrin resistant strain of tobacco budworm. Heliothis virescens (F), was crossed with a susceptible strain to determine the nature of inheritance of the resistance. Crossing of these highly resistant and highly susceptible strains showed susceptibility to permethrin to be auto trial and incompletely dominant. Backcrosses of F₁ progeny with resistant males indicated either that more than one gene is responsible for the resistance in this strain, or that the strain was not homozygous for resistance. It is likely that more than one locus is influencing permethrin resistance. The crosses and backcrosses performed provided relevant information for resistance management in the field.

Field populations of tobacco budworm. Heliothis virescens (F.). have been monitored annually since 1977 with topical applications of synthetic pyrethroid insecticides (primarily permethrin) and methyl parathion to detect changes in insecticide susceptibility. These data showed that LD₅₀'s fluctuated somewhat from year to year with permethrin. but with one possible exception. the fluctuations were not sufficient to change levels of expected control in the field. Field populations continue to show susceptibility to permethrin even though one Maricopa County population showed an increase in the LD₅₀ to 12.4 in 1988. Field populations continue to show resistance to methyl parathion and susceptibility to permethrin.