Direct-observation studies were conducted in replicated experimental plots to identify causes and estimate rates of mortality of whiteflies in cotton over the course of six generations from late June through late October. In plots receiving no whitefly or Lygus insecticides, predation and dislodgment were major sources of egg and nymphal mortality, and overall survival from egg to adult ranged from 0-18.2%. Similar patterns were observed in plots treated with the insect growth regulator (IGR) Knack. Applications of the IGR Applaud or a mixture of endosulfan and Ovasyn caused high levels of small nymph mortality and reduced rates of predation on nymphs during the generation immediately following single applications of these materials in early August. Whitefly populations declined to very low levels by mid-August in all plots, and few differences were observed in patterns of whitefly mortality among treated and control plots 4-6 weeks after application. The population crash was associated with an unknown nymphal mortality factor which reduced immature survivorship during this first posttreatment generation to zero. The application of insecticides for control of Lygus in subplots modified patterns of mortality in all whitefly treatments by generally reducing mortality from predation during generations observed from mid-July through August. Parasitism was a very minor source of mortality throughout and was unaffected by whitefly or Lygus insecticides.

Trehalulose and melezitose produced by Bemisia argentifolii Bellows and Perring and thermodetector counts in cotton lint increased with increasing numbers of days of exposure of open cotton bolls in infested cotton plots. Thermodetector counts were significantly correlated to amounts of trehalulose and melezitose. Rainfall of 0.5 inch reduced trehalulose and melezitose in cotton lint within 5 h following the rain. The results suggest dissolution of the sugars followed by runoff as opposed to microbial degradation.

When other means fail to avoid damaging levels of an insect pest population, chemical control becomes necessary. Chemical control is a variable farm input which should be optimized to reduce economic damage by the pest while maximizing profit and minimizing exposure to secondary pest outbreaks, pest resurgence, and risks of insecticide resistance. To best balance these needs, a grower or PCA needs the best information possible for selecting and timing chemical controls. This study examines the array of Lygus chemical control options currently available as well as experimental compounds that may or may not be available in the future. While identifying the best chemical controls is the major objective of this study, insights into proper timing and duration of control are also discussed. In short, there are few, yet effective, Lygus insecticides available to growers currently. However, with proper rates and timing, significant yield protection can be achieved with Orthene® or Vydate®. To a lesser extent, Thiodan® (endosulfan) was also effective against Lygus, though higher rates than used in this study may be necessary to achieve acceptable control. The use of mixtures did not enhance control of Lygus over our two standards (Orthene or Vydate). Newer compounds were also studied; however, Mirids (plant bugs) are not worldwide targets for development by the agrochemical industry. Thus, most new compounds are effective on some other primary pest (e.g., whiteflies, boll weevil, thrips, aphids), and control of Lygus is merely a potential collateral benefit. Of these, the chloronicotinyls (e.g., Provado®, Actara®) were not practically effective against Lygus hesperus, in spite of their existing or pending labelling. Their labels are based on demonstrated efficacy against a related species present in cotton outside of the West (Lygus lineolaris). One compound shows excellent promise as a Lygus control agent, Regent® (fipronil). Under development by Rhône- Poulenc, this insecticide provides as good or better protection against Lygus than our best materials. In a system demanding multiple applications to control chronic Lygus populations, Regent could be key to the development of a sustainable use strategy that does not over rely on any single chemical class. None of the insecticides tested significantly controlled adult Lygus, except after repeated use and time. Even then, this effect was likely the result of generational control of the nymphal stage which thus produced fewer adults over time. Nymphal control was excellent for Orthene, Vydate, and Regent. Yields were up to five times higher in the best treatments relative to the untreated control. Other effects were also documented for the best treatments which have additional positive impact on grower profitability: shorter plants (better defoliation), higher lint turnouts, less gin trash, and a lower seed index.

Temik 15G (6 lbs/acre) or Thimet 20G (8.2 lbs/acre) granular insecticides were applied to 40 inch rows in furrow at planting to cotton growing in Parker Valley, AZ. Moderate thrips pressure (0.5-1.5 thrips/plant) was experienced for the first eight weeks after planting and granular insecticide application. Temik provided better thrips control than Thimet for the first seven weeks after planting this study. Thrips control was similar for the two insecticides beyond eight weeks after planting. Temik application resulted in higher fruit retention levels measured up to 10 weeks after planting, compared to Thimet. However, fruit retention levels measured from 12 to 16 weeks after planting were similar for both Temik and Thimet when cotton plants compensated for early season square losses caused by thrips feeding.

Arizona pesticide use, as reported on the Department of Agriculture's form 1080, can be summarized to provide a rich picture of pest management in Arizona cotton. Limitations in the pesticide use reporting system complicate the process but do not undermine results. Overall pesticide use decreased over the period 1991 to 1998 despite a peak during the whitefly infestation of 1995. Decreases in insecticide use are responsible for most of the reduction in pesticide use. Recently released 1999 data indicates that reductions continued. Comparison of the composition of pesticide applications between 1995 and 1998 reflect the changes in pest control efforts. A new "target pest" category on the 1080 provides an even richer picture of pest management practices in Arizona cotton.

The gene for the Bacillus thuringiensis var. kurstaki (Berliner) insect toxic protein is a new advance in technology for pink bollworm (PBW), Pectinophora gossypiella (Saunders), control. We conducted studies in 1999 to investigate grower concern for reduced efficacy of NuCOTN 33b (Bt cotton) (Monsanto Company, St Louis, MO) in late-season because of breakdown or non-expression of the toxic protein. We compared the susceptibility of Bt and Deltapine 5415 (Monsanto Company, St Louis, MO) (non-Bt) cotton bolls to PBW at periodic intervals during the first and second cotton fruiting cycles. We placed >200 PBW eggs per boll on the inside surface of bracts of susceptible immature cotton bolls. The artificially infested bolls were later harvested and examined for evidence of PBW infestation. High percentages of both Bt and non-Bt cotton bolls had numerous larval entrance holes in the carpel walls of the bolls. Less than 1% of the Bt cotton bolls and over 70% of the non-Bt cotton bolls were found with living PBW larvae. Bt cotton bolls of the late-season second fruiting cycle were as resistant to PBW infestation as Bt cotton bolls of the first fruiting cycle.

Sprays of commercially-procured sugars that are also found in silverleaf whitefly Bemisia argentifolii Bellows and Perring [= B. tabaci (Gennadius) Strain B] honeydew were applied to clean cotton lint to determine the relationship between the sugars and cotton lint stickiness. Increasing concentrations of the sugars resulted in increasing thermodetector counts.

In 1996, two Insect Growth Regulators (IGRs), pyriproxyfen (Knack®) and buprofezin (Applaud®) became available to Arizona cotton growers for control of whitefly, Bemisia argentifolii under a Section 18 EPA exemption. This study makes use of a section-level database to examine (a) factors explaining IGR adoption and (b) how adopters of IGRs altered their overall insecticide use to control whiteflies. IGR adoption can be explained to a large extent by location effects. Adoption was more likely on sections where an index of whitefly susceptibility to synergized pyrethroids was low and on sections with higher whitefly control costs in the previous year. Adoption was inversely related to local population density. On sections where growers adopted IGRs, expenditures on synergized pyrethroid and other whitefly-specific tank mix applications fell by $62.52 per acre. On sections with no IGR adoption, tank mix expenditures fell less, by $44.37 per acre. On adopting sections, net costs of controlling whiteflies fell by $29.62 per acre, or by over $11,000 per farm.

Changes in insecticide use, available pest control technologies, and local crop ecology together with severely depressed cotton prices place a renewed premium on Lygus control decision aids for Arizona cotton. As part of an on-going program to develop research-based Lygus management recommendations, we investigated the impact of various timings of chemical controls on Lygus population dynamics, number of sprays, costs of control, and net revenue as well as cotton heights, trash, lint turnouts, and yields. Once there were at least 15 total Lygus per 100 sweeps, sprays were made according to the number of nymphs in the sample (0, 1, 4, 8 or 16 per 100 sweeps). Up to 7 sprays were required (15/0 regime) to meet the needs of the target threshold. Lygus adult densities were largely unresponsive to the treatment regimes or individual sprays made. Three generations of nymphs, however, were affected by the treatments with the ‘15/4’ regime harboring the fewest nymphs through July. This ‘moderate’ regime required 4 sprays and had the shortest plants, cleanest harvest, and highest lint turnouts. In addition, this regime out-yielded all other treatment regimes including the 6- (15/ 1) and 7- (15/0) spray regimes. Regression analyses of the data suggest that adult Lygus are less related to yield loss than nymphs and that large nymphs are best correlated with yield loss. Thus, spraying based on adults only would appear illadvised. Returns were highest ($747/A) for the 15/4 regime with over $100 more than the more protective regimes. Thus, there is no economic advantage in advancing chemical control when nymph levels are low. Maximum economic gain was achieved by waiting for the 4 nymphs per 100 level (with 15 total Lygus/100; 15/4) before spraying. However, waiting too long (beyond the 8 nymphs / 100 level; 15/8) resulted in significant reductions in yield and revenue. Our recommendations, therefore, are to apply insecticides against Lygus when there are at least 15 total Lygus, including at least 4 nymphs, per 100 sweeps. These recommendations are stable over a wide variety of economic conditions (market prices & insecticide costs). Continued work is necessary to verify these findings over a wider range of cotton developmental stages, varieties, and other environmental conditions.

We studied silverleaf whitefly (SLW) and trichome density relationships on ten selected upland cotton cultivars: Deltapine #20B, 50B and 90B, NuCOTN 33B, Stoneville 474, Fibermax #819 and 832, Siokra L-23, and 89013-114 at Maricopa, in AZ, 1999. Whitefly and stellate trichome densities were counted on leaves on main stem leaf nodes #1, 3, 5 and 7 of each cultivar. Stoneville 474 had about 2-3 times more eggs, nymphs, and adults and also had 3-30 times more branched trichomes on abaxial leaf surfaces compared with the nine other cultivars. The top young leaves on node #1 had about 6 times more stellate trichomes compared with older leaves. However, the top young leaves also had reduced numbers of eggs and nymphs (23 and 1/cm2 of leaf disk, respectively) compared with older leaves. The results suggest that other factors, in addition to trichomes, at least for young terminal leaves, affect silverleaf whitefly population development.