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.

A bioassay developed by one of the authors (MY) in 1993 was used to monitor susceptibility of sweetpotato whitefly to Applaud in five different field locations. Whitefly populations were exposed to from 0 (untreated fields) to 4 (small plot trial) applications of Applaud. Susceptibilities of whiteflies, as measured by LC₅₀s and LC₉₅s, did not increase with exposure to Applaud (0 to 4 applications) nor since baseline measurements of susceptibility were made in 1993. Under current patterns of use (single use), risk of resistance to Applaud appears to be minimal.

We developed a sampling protocol for nymphs of the sweetpotato whitefly for timing the application of insect growth regulators. These plans require counting the number of large, visible nymphs within a 3.88 cm² leaf disk on the fifth main stem node leaf down from the terminal. Use of insect growth regulators for whitefly control is recommended when whitefly densities from 30 plants average 0.5 - 1.0 large nymphs per disk and 3 - 5 adults per leaf. We evaluated these sampling and decision- making plans within a large -scale field experiment. Precision was adequate for densities of 1.0 large nymph per leaf and greater, but sample sizes greater than 30 are needed for lower densities. The ability of samplers to detect and categorize nymphal instars and sampler-to-sampler variation in this ability were significant sources of variation. A binomial (presence/absence) sampling plan may diminish sampler-sampler variation while increasing efficiency and accuracy of decision- making.

The section 18 granted for the use of insect growth regulators in 1996 in Arizona provided an excellent opportunity to demonstrate the efficacy of the materials. Knack® (Pyriproxyfen) and Applaud® (Buprofezin) both demonstrated excellent control of whitefly in this demonstration. Efficacy of the insect growth regulators was monitored by using the "Ellsworth-Naranjo" methods of measuring adult and nymph whitefly numbers. This method provided good tracking of the populations throughout the period monitored. The areas treated were cotton variety trials both pima and upland. On the upland trial whitefly infestation data was collected on each variety. Hairy leaf varieties tended to have higher whitefly numbers of both adults and nymphs.

Cotton plant densities of 10 or 40 thousand plants/acre had no effect on numbers of silverleaf whitefly, Bemisia argentifolii Bellows and Perring, adults, eggs, nymphs, extracted sugars from lint samples or thermodetector sticky cotton counts. Higher numbers of whitejlies occurred in early-season in Pima S-7 cotton than in DPL 50 or DPL 5415 cotton. Seasonal averages for sugars, percentages of total reducing sugars and thermodetector counts were higher for DPL 50 compared with Pima S-7 but not DPL 5415. Insecticide treatments reduced thermodetector counts and associated sugars extracted from lint.

At pre- sowing irrigation (mid-March), cotton fields were treated with two entomopathogenic nematode species; Steinernema riobravis and S. carpocapsae for control of diapausing Pectinophora gossypiella larvae. Pima S-6 cotton fields situated in Fort Hancock, Texas were treated at a rate of one billion nematodes per acre. Caged, diapausing larvae were buried in fields at a depth of one inch, in row tops and furrow bases. Nematodes were applied with a spray rig, fixed winged aircraft, or in furrow irrigation via a constant flow, battery box. Fields were irrigated after ground application, prior to aerial spraying and during furrow application. Caged larvae were recovered 48 hours after nematode application. All application methods resulted in uniform distribution of nematodes over the treated fields. No significant differences ir. larval mortality between nematode species or application method could be determined. However, aerial and furrow application methods gave consistently better parasitism of larvae compared to ground rig delivery. Larval mortality in cassettes buried in furrow bases was significantly higher than in row tops. Larval mortality ranged from 53.26-79.14 %. Both nematode species could be recovered 50 days post application. At pin-head square Frustrate® PBW pheromone bands (biosys, Inc.) were applied at 100 bands per acre placement rate (16 g a. i./acre), giving a target release of 115 mg gossyplure/acre/day. Capillary gas chromatography was used to analyze bands throughout the growing season. A uniform release profile indicated sufficient release of pheromone for 144 days after placement. Pink bollworm mating disruption was monitored in three ways: 1. Delta 2 traps were positioned throughout the farm, forming a continuous trap line. Significantly larger numbers of moths were recovered form untreated zones. 2. Virgin female moths were placed in mating stations at dusk. At sun rise moths were collected and later dissected for spermatophores. Significantly higher mating activity occurred in untreated fields (p= 0.000). 3. Green bolls were collected at random and examined for larvae. Significantly higher infestation levels existed in untreated zones. At harvest (November), seed cotton yields were weighed using trailer scales. Higher yields were recovered from pheromone (1,864 lb/acre), and pheromone + nematode fields (1,712 lb/acre), than control fields (1,450 lb/acre). However, due to large variations between fields, the differences were not statistically significant (p = 0.436).

The Cry1Ac gene (Bollgard®) is available in cotton either alone ('B') or in combination (Bollgard II®) with a second gene, Cry2Ab ('X'). We evaluated these two different transgenes, separately and together, in near isogenic lines of the upland cotton variety ‘DP50’. DP50B was previously transformed with the Cry2Ab gene to give rise to the experimental line 985BX which was then back-crossed to DP50 to produce near isogenic single gene variants, 985B and 985X. The lepidopteran target was pink bollworm (PBW), Pectinophora gossypiella (Saunders), which was evaluated in two field studies through a series of samples from artificially and naturally-infested bolls. In one study (NTO), three cotton lines (DP50, DP50B, 985BX) were evaluated under three spray regimes. In the second study (Isoline), five near isogenic lines (DP50, DP50B, 985B, 985X, 985BX) were evaluated under two spray regimes: fully sprayed and lepidopteran unsprayed. In lines containing only one transgene, Cry1Ac or Cry2Ab, bolls had consistently fewer PBWs than the non-Bt variety. Very few PBWs developed into large (3rd instar) larvae in these Bt varieties. The majority (NTO: 83%; Isoline: 94%) of PBWs recovered were dead first instar larvae. Less than 5% of the DP50B bolls in the NTO study were infested with feral large (≥3rd instar) larvae, and large larvae were present in less than 2% of naturally-infested bolls of single-gene lines in the Isoline study. PBW age and mortality distributions confirmed that the single transgenes were effective in stopping PBW development and killing young instars. Cry2Ab displayed a broader spectrum of efficacy as it was significantly more effective against citrus peelminer (Marmara spp.), an incidental lepidopteran present in high densities in the tests. The two-gene (Cry1Ac + Cry2Ab) line showed better (at least 10-fold) efficacy than the single-gene lines against PBW large larvae infestation. The PBW age distributions found in this variety consisted almost entirely (98%) of dead first instar larvae. Less than 0.6% of the bolls of the two-gene variety in the NTO study were infested with large (≥3rd instar) larvae, and there was no infestation by large larvae in any of the naturally-infested bolls in the Isoline study. Yields and other agronomic parameters of the two-gene and single-gene varieties were superior or similar to the null parent. Second pick yields of all Bt varieties were significantly higher than the recurrent parent non-Bt line, suggesting a high degree of efficacy against typically high PBW densities during the late season. Cotton lines with transgenes (Cry1Ac & Cry2Ab) separately and combined demonstrated a high degree of efficacy and agronomic performance for usage in Arizona against PBW. The ramifications of isogenic comparisons of PBW incidence on efficacy and resistance monitoring are discussed.

Pink bollworm (PBW), Pectinophora gossypiella (Saunders), larval mortality after different times of confinement on NuCOTN 33B® (Bt) cotton bolls were compared with larval mortality on Delta and Pineland 5415 cotton bolls as controls. We also compared larval mortality on different age cotton fruiting forms and determined the Bt susceptibility of different age PBW larvae. Infesting Bt bolls with PBW eggs that hatched within 24 h resulted in 92% larval mortality after 48 h and 100% mortality in 4 days or longer. There were no differences between cultivars in numbers of larval entrances holes into bolls. Generally, days to pupation for both males and females were longer on Bt bolls compared with non-Bt cotton. There were no significant mortality differences for larvae feeding on Bt fruiting forms of different ages ranging from one-half grown flower buds to 40-day old immature green bolls.

Cotton aphid, Aphis gossypii Glover, fecundity, nymph development and honeydew production were studied in the laboratory. Apterous adult females produced an average of 1.7 nymphs per day and the nymphs (four instars) developed to adults in an average of 4.1 days at 26.7° C in the laboratory. Average longevity of adults was 16.1 days. More honeydew drops were produced by one-day old nymphs than three- or four-day old nymphs. Numbers of honeydew drops produced on a day to day basis were highly variable and did not show a distinct pattern of production. More honeydew drops, sugars and progeny were produced by adults at 26.7° C compared with 15.6 or 32.2° C. Increasing times of exposure of clean cotton lint to aphids and the resulting increasing amounts of honeydew sugars under laboratory and field conditions were significantly related to increasing cotton lint stickiness as measured with a thermodetector.

Three studies were conducted over the two year period to explore the effectiveness of using pyrethroid insecticides only vs. rotating insecticide chemistries between the pyrethroids and organophosphates on both long and short staple cotton varieties. These same treatments were also evaluated over Bt and non-Bt varieties. In the worst case scenario, where weather conditions prevented timely application of insecticides and effectiveness of insecticides applied, long staple cotton yielded around 1/3 bale per acre after six insecticide applications. Within 200 feet of this experiment, during the same cropping season, with the same insecticides applied, DP 90B (a Bt variety) produced 3 bales per acre. Details of these studies are contained in this report.