Two insect growth regulators (IGRs) that are selective against whiteflies (Aleyrodidae) became available for the first time in 1996 to Arizona cotton growers under emergency exemption. These IGRs were studied in a commercial -scale whitefly management trial (178 acres) in 1996. The trial was designed to evaluate provisional whitefly recommendations. Three sets of factors were tested in a 48 plot factorial design: application methods, thresholds for initiating IGR use, and insecticide regimes. Ground (broadcast at 15 gallons/acre) and aerial applications (5 gallons/acre) were roughly equivalent over a wide range of variables examined (whitefly populations, number of sprays, cost, and yield). Under the higher population densities, ground applications sometimes suppressed whiteflies to a greater extent than aerial applications. The rapid advance of the population resulted in the initial triggering of all thresholds within just five days. No consistent trend in population suppression was seen for the thresholds tested (0.5, 1.0 and 1.5 large, visible nymphs per 3.88 sq cm leaf disk located between the major and first, left lateral vein of the fifth main stem node leaf below the terminal). The control cost for the highest threshold was significantly less than for the middle threshold, but not for the lower threshold. Under emergency exemption, each IGR may be used only once per season. The sequence of use did not result in any consistent advantage in population suppression, cost, number of sprays needed, or yield. The IGR regimes were in general more efficacious, less disruptive, and less costly than the conventional insecticide regime. There were significantly fewer sprays needed by the IGR regimes compared to the conventional regime. All regimes successfully controlled whitefly populations for a 12 week period and cost significantly less than conventional programs tested in 1995 (Ellsworth et al. 1996a). IGRs are effective, long-lasting, and less environmentally disruptive alternatives to conventional insecticides. They reduce the risk of secondary pest outbreaks and pest resistance, and increase the opportunity of natural enemy conservation.

The insect growth regulator, Knack was evaluated for efficacy against sweetpotato whitefly in paired plots within three commercial cotton fields near Somerton, Arizona. A single application of Knack and Danitol/Orthene was made in July and the impact on whitefly populations, natural enemies and secondary pests was measured for 40 d. Knack appeared to act slowly during the first 2 weeks, but after 21 days nymph populations were greatly reduced. Populations of nymphs and adults began to return to their pre-test levels after 40 d. The Danitol/Orthene application resulted in a significant decrease in adult numbers. Initially nymph densities declined, but after 14 d densities appeared to increase at a much greater rate than was observed in the Knack plots. Under the conditions experienced in this study, a single application of Knack in early July provided protection against sweetpotato whitefly as good, or better than experienced with Danitol/Orthene. Reductions in yields or lint quality attributable to whitefly were not observed in either treatment regime. Although beneficial predators were measured throughout the season, insecticide sprays for lygus control prevented significant buildup of populations. However, the numbers of Liriomyza leafminer adults captured on sticky traps were significantly lower in Knack-treated plots.

In 1995, silverleaf whitefly, Bemisia argentifolii Bellows and Perring, resistance to the widely -used mixture of Danitol® (fenpropathrin) + Orthene® (acephate) was shown to be severe and widespread in Central Arizona cotton. Thereafter, laboratory experiments were undertaken to identify the other major insecticides that were affected by this resistance. Whiteflies were collected in November of 1995 from Maricopa (highly resistant) and Yuma (relatively susceptible) County locations in Arizona. A composite colony was established by combining Yuma and Maricopa whiteflies in a 4:1 ratio. After six generations of adult selection of this population with Danitol + Orthene, appreciable shifts in the concentration responses for pyrethroid, organophosphate, and carbamate insecticides were observed, indicating heritable variation for resistance in the source populations. From this we obtained definitive proof that resistance to Danitol + Orthene confers cross-resistance to Asana® (esfenvalerate), Capture® (bifenthrin), Danitol, Decis® (deltamethrin), Decis + Orthene, and Karate® (lambda-cyhalothrin). Additionally, selection with Danitol + Orthene resulted in statistically significant reductions in susceptibility to Curacron® (profenofos), Lannate® (methomyl), Monitor® (methamidaphos), and Ovasyn® (amitraz). Studies were performed to assess tolerance of Maricopa (pyrethroid- resistant) and Yuma (pyrethroid-susceptible) populations to a diversity of conventional insecticides currently registered for use in Arizona cotton, with the intention of finding compounds that showed promise for overcoming pyrethroid resistance. Of the materials evaluated, Curacron, Lannate, Lorsban® (chlorpyrifos), Ovasyn, Supracide® (methidathion), and Vydate® (oxamyl) were most promising. To determine to what degree pyrethroid resistance in cotton influenced resistance in winter vegetables and melons, and vice versa, whitefly populations were collected from a succession of these crops in Western and Central Arizona regions. In most instances, the whiteflies in Western Arizona were significantly more susceptible to Danitol + Orthene than those in Central Arizona. Significant decreases were found in susceptibility to Danitol + Orthene during the 1996 season at three of the four locations in which multiple crops were monitored. This emphasizes that pyrethroid resistance levels can be increased in whitefly populations from any of the cotton, melons, or other winter vegetable crops evaluated. Therefore, management of pyrethroid resistance in Arizona cotton will require harmonizing resistance management efforts and specifically limiting pyrethroid use in the entire crop complex.

As part of a large-scale, multi-institutional experiment in 1996 to examine and demonstrate strategies for management of Bemisia tabaci involving the use of two insect growth regulators (IGRs), we evaluated effects on the abundance and activity of native natural enemies. For parasitoids there were significant differences between insecticides regimes on 4 of 10 sampling dates. In general, parasitoid abundance and rates of parasitism were depressed in treatment plots receiving a rotation of conventional chemistry in comparison with those receiving IGRs. There was no apparent effect of any of the treatment variables on parasitoid emergence (immature survival). Results for arthropod predators are still preliminary, but densities were generally depressed in plots receiving a rotation of conventional insecticides in comparison with those receiving IGRs. These preliminary results suggest that use of IGRs for suppression of B. tabaci may help conserve populations of important natural enemies.

Bolls from transgenic cotton, NuCOTN 33 (Delta and Pine Land Co.) containing the Bollgard™ gene (Monsanto Co.) and from the parental cultivar DPL-5415 were examined for mature larvae of the pink bollworm (78,240 total bolls). Bolls from paired fields were collected in the Queen Creek, Buckeye, Maricopa, and Marana, AZ, areas. Equal numbers of bolls were collected from the edges of each field each week July - October except for Marana where a single collection was made 30 October. Bolls were incubated for 2 weeks and/or dissected from 1 September onward. Numbers of pink bollworm larvae were very low in all fields through August and increased to extremely high levels (up to 3.4 larvae/boll at Marana) in some control fields in October. Numbers of pink bollworm found in NuCOTN 33 were extremely low or nonexistent, even in fields immediately adjacent to heavily infested control fields. The overall numbers of larvae found in NuCOTN 33 were comparable to those found in 1995. In 1995, the percent worms of bolls were: NuCOTN 33 = 0.0003 (13 larvae /38320 bolls) compared to 11.80% for DPL -5415 (4711 larvae /39920 bolls). Overall percent worms of bolls for 1996 were: NuCOTN 33 = 0.0004% (14 larvae/33350 bolls) compared to 34.19% (11572 larvae/33850 bolls) in DPL-5415.

Transgenic cotton with the Bollgard™ gene inserted has shown great promise in controlling pink bollworm infestations in cotton. This trial was superimposed over a variety trial. Evaluations of pbw infestation indicated remarkable control even though the bolls became infested. Yields were increased in this trial when almost 100% infestation of pbw was allowed to occur. It appears that the trangenic cottons containing Bollgard™ may be an effective method of pbw control.

Under field conditions, pink bollworm (PBW), Pectinophora gossvpiella (Saunders), larvae were exposed to soil samples from plots treated with Steinernema riobravis at the rate of 5 nematodes per cm² of soil surface. Larval mortalities were 50% on the day of treatment and 2.5% on day 90 following treatment with irrigations about every 14 to 21 days,. Larval mortality percentages after exposure to soil samples from plots treated with S. carpocapsae at the rate of 5 per cm2 of soil surface were 32.5, 15.3, 5.3 and 2.5 for the day of treatment and day 1, 7, and 15 following treatment, respectively. No further mortality occurred in bioassays conducted up to 90 days following treatment. With plots treated with 25 nematodes per cm² of soil surface, PBW larval mortalities ranged from 100% on the day of treatment to 7.5% on day 63 following treatment with S. riobravis and 92.5% on the day of treatment to 5% on day 7 following treatment with S. carpocapsae. Percentages of larval mortality after exposure to soil samples from plots treated with S. riobravis increased after each irrigation, but did not increase after exposure to soil samples from plots treated with S. carpocapsae.

Adult lygus bugs, Lygus hesperus (Knight), were collected from alfalfa fields in 22 different cotton producing areas of Arizona. A standardized, glass vial method was used to estimate susceptibility of the collected populations to the pyrethroid insecticide Captures (bifenthrin) and the organophosphate Orthene® (acephate). Large differences were recorded in susceptibility of Arizona populations to both insecticides. The most susceptible lygus populations continue to be found in the eastern areas of the state and the least susceptible in central Arizona. Lygus from throughout the state were substantially more susceptible to Capture and Orthene in 1996 than in 1995. Lygus bioassayed repeatedly from the same locations in 1996 exhibited moderate-to-small seasonal variability in susceptibility to Capture. However, some of the same populations varied widely in susceptibility to Orthene in 1996. The large changes in susceptibility to Orthene were attributed to episodic movements of lygus from other hosts. Eleven insecticides were evaluated against populations most and least susceptible to Capture and Orthene to identify promising candidates for future lygus field trials. A Safford population was substantially more susceptible than a Maricopa population to Admire®, Curacron®, Cygon®, Malathion® and Vydate®. Most surprising was the greatly reduced susceptibility to Admire of the Maricopa population. The older insecticides Bidrin®, Lannate®, Monitor ®, Naled®, Ovasyn® and Thiodan® were quite similar in toxicity to both the Safford and Maricopa populations and therefore are good candidates for further field evaluations to judge their merit for inclusion in lygus insecticide rotations. Bioassay results were related to field performance of four insecticides in a field trial conducted in Central Arizona. Findings showed that the two insecticides that caused the lowest mortality in vial bioassays, Orthene and Vydate, resulted in the greatest suppression of lygus in the field. These findings underscore that the absolute level of mortality observed in bioassays should not be assumed to reflect relative efficacy in the field. It also confirms that Orthene and Vydate continue to be good choices for lygus control, even in Central Arizona where populations are decidedly less susceptible to these insecticides. We have demonstrated that the adult vial bioassay provides a reliable method for measuring differences between Arizona lygus populations in susceptibility to a broad range of conventional insecticides. We found the method sufficiently sensitive to repeatedly detect significant within-season and regional differences in lygus susceptibility. These new insights will allow us to better manage the insecticides used in Arizona to control this important pest.

Temik 15G was side -dressed at a rate of 7 lb./acre and 14 lb./acre and compared to an untreated check in two experiments in Buckeye, Az.. Treatments were made prior to the second in- season irrigation (June 3 and June 5) which was just prior to early bloom. Lygus counts were taken using a sweep net on weekly intervals for six weeks post application. The first experiment resulted in a significant increase of 123 lb. and 1241b. lint in both the 7 and 14 lb. rate treatment respectively over the untreated check. The second experiment resulted in a significant 102 lb. lint increase for the 7 lb. treatment with no significant difference for the 14 lb. treatment to the check.

We summarize a whitefly resistance crisis that culminated in 1995 in Arizona cotton and that prompted the development of an integrated resistance management strategy. The strategy incorporated two new major elements: once-per-year use of the insect growth regulators (IGRs), Knack® (pyriproxyfen) and Applaud® (buprofezin), and measures to delay use of pyrethroids for as long into the growing season as possible. A three-stage chemical use recommendation was formulated comprising IGRs (Stage I), other non-pyrethroid insecticides (Stage II), and synergized pyrethroid insecticides (Stage III). Results from use of the strategy in the 1996 season were very promising. Insecticide use for control of whiteflies was reduced substantially where IGRs were used. Statewide monitoring of whitefly susceptibility to key insecticides revealed significant reductions in resistance to synergized pyrethroids as well as to non-pyrethroid insecticides. Resistance to Danitol® + Orthene® was shown to decline sharply from the end of the 1995 season to early in the 1996 season at the Maricopa Agricultural Center. Use of Stage I materials (Knack® and Applaud®) and specific Stage II (non-pyrethroid) insecticides in 1996 resulted in only small reductions in susceptibility to synergized pyrethroids. However, one application of Danitol® + Orthene® yielded a large increase in resistance. These findings confirmed the value of the newly formulated resistance management strategy and indicated that resistance to the synergized pyrethroids can be managed if these insecticides are used sparingly. Additionally, evidence was obtained of collateral resistance buildup and decline in lygus bugs and whiteflies. Substantially reduced susceptibility of lygus bugs was documented in 1995, relative to 1994, coinciding with elevated insecticide use to control resistant whiteflies. Implementation of the 1996 whitefly resistance management program was correlated with increased lygus bug susceptiblity to the insecticides Orthene® and Capture® at most locations monitored throughout Arizona.