Several designs for yellow sticky traps where placed on the periphery of cotton and lettuce fields and evaluated to determine the most efficient type for capturing bandedwinged and sweetpotato whiteflies. Cylindrical traps caught more (55% of the total) than the other designs; upward-facing horizontal traps caught 26 %, vertical traps 16% and downward- facing horizontal traps 3 %. The number of both species of whiteflies captured by the various designs placed around fields was compared with the number caught on traps in lettuce field interiors. Catches from cylindrical and upward-facing horizontal traps were consistantly correlated at high levels with field populations. Traps placed at ground level caught a significantly higher number of whiteflies when compared with those placed at 50 and 100 centimeters (81% of the total versus 11% and 7% respectively). Aerial traps displayed more variation with field populations than did ground level traps.

Reproductive traits of wasp parasitoids are thought to be strong indicators of their success as biological control agents. Our study looks at the number of eggs produced by the whitefly parasitoid Eretmocerus eremicus. A series of experiments conducted on female wasps reared in the absence of whitefly hosts demonstrated that adult wasps emerge with a large (approximately 54) number of eggs that is retained during the first 2 days of adult life. Eggs are then absorbed steadily until at least 8 days following emergence. The results of this study suggest that the mode of egg production exhibited by E. eremicus is the type where they emerge with all, or nearly all, of their eggs, i.e. they do not produce additional eggs as they age. This information is significant when considering how they find their whitefly hosts and how effective they might be in controlling whitefly numbers.

Studies to examine lettuce aphid population growth on Admire and Platinum treated plants were conducted on head lettuce at the Yuma Agricultural Center. By artificially infesting plants on several lettuce plantings during the spring, the influence of insecticide residual and temperature were measured. Results of five field trials suggest that both Admire and Platinum can have a significant influence on lettuce aphid population growth. Depending on timing of infestation and insecticide residual, significant suppression of population growth can result from the application of these compounds. Infestations initiated at 28 d following Admire application initially resulted in minimal population growth, but later allowed aphids to reproduce at high numbers. In both cases, Admire provided about 90% control of the lettuce aphid population. However, aphid infestations occurring at later periods of plant residual almost always resulted in higher population development. In addition, these studies also support conclusions drawn form last season that suggested lettuce aphid population growth is greatest when ambient temperatures average between 65-70 ºF.

Studies were conducted in the laboratory to investigate how the addition of a insecticides to two sources of Colorado River water would effect the pH of spray mixtures. In addition, we were curious what the effects of various labeled concentrations of buffers, acidifiers, spreader/stickers, and foliar nutrient sprays would have on the pH of spray water. Results showed that in most cases, spray concentration remained alkaline following addition of insecticides and adjuvants, with variations occurring primarily for the OPs. Buffering agents dramatically lowed pH at concentration greater than 0.25% v/v. Studies were also designed to evaluate the knockdown and residual mortality of Success against worms when applied in an acidic spray solution. Bioassays of larval mortality on field-treated foliage showed that knockdown mortality was not affected, but residual efficacy was significantly reduced when Success was applied using acidic (pH 4.2) spray solutions.

Studies were conducted to compare the residual field efficacy of Calypso, compared with soil applications of Admire and foliar sprays of Provado and Actara. The results demonstrate that several insecticide product uses are being developed that offer melon growers management alternatives for controlling whiteflies comparable to what they have experienced with Admire. Calypso showed excellent promise as a foliar, post-planting spray with good residual activity. Two spray applications provided good whitefly control and excellent crop and melon quality. Although we saw a measurable impact on some natural enemies, the compound is supposedly very safe to honeybees. Overall, when directed at low adult and immature densities, Calypso provided 14-21 days of residual control and was capable of preventing yield and quality losses in spring melons. These studies also emphasize, that like the IGRs, these foliar neonicotinoids should be used when whiteflies densities are low and beginning to build. This compound may be available as early as 2002.

Susceptibility of beet armyworm, Spodoptera exigua Hübner, to the Bt toxin, Cry1Ac, expressed in the first generation of transgenic cotton plants was evaluated using a laboratory strain and several foreign and United States field strains. A diet-incorporation assay of neonate larvae was used. Susceptibility was estimated by the degree to which Cry1Ac inhibited larval growth from the first through fifth instar. Regression analyses of larval weights against log concentration of Cry1Ac yielded slope and intercept values that were used to compute I₅₀s, defined as the amount of Cry1Ac that resulted in a fifty percent reduction in larval growth. Three populations exhibiting reduced susceptibility to Cry1Ac were selected on diet containing 1000 micrograms of Cry1Ac per gram of diet. I₅₀s for non-selected populations ranged from 0.0477 micrograms Cry1Ac per gram of diet for the laboratory reference strain to 4.31 micrograms of Cry1Ac per gram of diet for a field strain collected from Yuma, Arizona. Selection of a strain from Belle Glade, Florida, with Cry1Ac yielded the lowest susceptibility to this toxin. Prior to selection, the I₅₀ was 2.43 micrograms of Cry1Ac per gram of diet; after selection the I₅₀ was 17.4 micrograms of Cry1Ac per gram of diet. Thus selection reduced susceptibility of the Belle Glade, Florida strain to Cry1Ac by 7.2-fold and yielded susceptibility that was 360-fold less than the laboratory reference strain. Selection also reduced susceptibility of an Arizona (Dome Valley) population by 3-fold. Our results demonstrate the presence of large (>25-fold) differences in susceptibility of field-collected beet armyworm populations to Cry1Ac. Furthermore, the fact that resistance was elevated three to seven-fold in two selected strains provided evidence of a genetic basis of resistance to Cry1Ac.

Several small-plot field studies were conducted at the University of Arizona, Yuma Agricultural Center in the spring 2001 growing season to evaluate various neonicotinoids and azadirachtin products against lettuce aphid, Nasonovia ribisnigri, in lettuce. Further, these products were compared as soil-applied treatments, foliar sprays and application through sub-surface irrigation. The results of these trials provide useful information for understanding how to effectively use the new chemistries available for aphid management in lettuce. First, Platinum performed best as a post-planting application through a side-dress application or through the drip. The foliar neonicotinoids, Assail and Actara were active against lettuce aphids, but were most effective when populations densities were lower. Comparatively, the conventional chemistries (MSR, Orthene/Provado, Provado/Endosulfan) provided consistent control when used aggressively. The azadirachtin products were significantly less effective against LA in head lettuce due largely to their inability to contact the insects, but on formulation (AzaDirect) showed better efficacy when applied through drip irrigation or sprayed repeatedly in romaine lettuce.

Arizona cotton experienced a severe crisis in 1995 stemming from resistance of whiteflies to synergized pyrethroid insecticides. The insect growth regulators (IGRs), Knack® (pyriproxyfen) and Applaud® (buprofezin), served a pivotal role in resolving this problem. Similarly, Admire® (imidacloprid), the first neonicotinoid insecticide to obtain registration in Arizona, has been the foundation of whitefly control in vegetables and melons. In this paper we provide an update regarding the susceptibility to key insecticides of whiteflies from Arizona cotton, melons, and greenhouses. Overall, whitefly control in Arizona cotton remained excellent in the 2000 season and there were no reported field failures. However, there was a significant decrease in susceptibility to Applaud of whiteflies collected from cotton. One collection from Eloy, Arizona, in 2000 had susceptibility to Applaud that was reduced 129-fold relative to a reference strain. Whiteflies resistant to Knack, detected for the first time in Arizona in 1999, were again detected in 2000 but at lower frequencies than in 1999. Though whiteflies resistant to Admire/Provado® continued to be found at specific locations, overall susceptibility to Admire/Provado in 2000 remained high in whitefly collections from cotton. The new neonicotinoid insecticides, thiamethoxam and acetamiprid, were similar in toxicity to Arizona whiteflies in laboratory bioassays and we confirmed the significant but relatively low-order cross-resistance we previously reported between these neonicotinoids and Admire/Provado. Arizona whiteflies continued to be relatively susceptible to mixtures of Danitol® (fenpropathrin) and Orthene® (acephate). Factors that could undermine the current success of whitefly resistance management in Arizona are discussed. These include: 1) more severe resistance to IGRs in whiteflies from cotton, stemming from increased IGR use within and outside of cotton; 2) resistance of vegetable, melon and greenhouse whiteflies to the various formulations of imidacloprid (Admire, Provado, Merit®, Marathon®); 3) the imminent registration of new neonicotinoid active ingredients in cotton, greenhouses and other Arizona crops.

Studies were replicated over 2 years to further evaluate the residual efficacy of several selective, reduced-risk compounds that are now registered for use in head lettuce. In most cases, the Success, Proclaim, Avaunt and Intrepid provided excellent seasonal efficacy against beet armyworm and cabbage looper larvae. Their performance at stand establishment and harvest were also examined. Based on the results of these studies and additional trials conducted over the past several years, we now have sufficient information for optimizing their uses in our lettuce pest management program. Because they are uniquely different insecticide chemistries, they can be rotated throughout the season to prevent the rapid buildup of resistance. A table was constructed that offers suggested uses for each compound throughout the season. The results are ultimately are aimed at assisting growers and PCA’s in making sound decisions on choosing compounds for use in controlling beet armyworm and cabbage looper in head lettuce.

Several relative sampling techniques (direct visual counts, beat pans and sticky traps) were compared to absolute counts (plant wash) to determine sampling reliability for estimating western flower thrips population levels in lettuce. In numerous plantings of experimental plots of head lettuce, the relative sampling methods indicated similar thrips population trends throughout the season and all relative estimates of abundance were significantly correlated with absolute densities. However, both relative methods could only account for a proportion of the adult thrips infesting head lettuce plants, where they estimated about 30% of the actual absolute population. For larvae, beat pan sample estimated about 18-20% of the actual population density, whereas direct visual counts accounted for less than 10% of the thrips present. Comparison of sampling methods in insecticide efficacy trials indicated that beat pan and direct visual counts did not always accurately estimate treatment differences for adult. For densities of thrips larvae however, beat pan and visual counts methods did consistently provide accurate estimates of treatment differences in efficacy trials. Overall, both beat pan and direct visual count procedures are reliable thrips sampling methods that will generally provide precise estimates of thrips abundance necessary in lettuce pest management programs. Furthermore, these methods, and the beat pan in particular, also may serve as effective research tools that provide reliable estimates of treatment differences.