Key Pest Of Cotton Research Articles

Predatory Efficacy of Cotton Inhabiting Spiders on Bemisiatabaci, Amrascadevastans Thripstabaci and Helicoverpa armigera in Laboratory Conditions

Distinction of predator's diet and prey choice preference is a hot topic of current investigations. Spider being generalist predator and cosmopoliter in nature acts as biological control agent in many agro-ecosystems. In the current study, predatory efficacy of five spiders (Pardosa birmanica, Cyclosa insulana, Thomisus projectus, Plexippus paykulli and Lycosa terrestris) inhabiting the cotton fieldevaluated in the laboratory conditions maintained at (27±2)°C temperature, 65%±5% relative humidity and 12 : 12 h of light and dark photoperiod. Four key cotton pests' viz. Bemisiatabaci, Amrascadevastans Thripstabaci and Helicoverpa armigera were utilized in the choice and no-choice predatory studies. The findings of current investigation revealed that each predatory spider utilized at least one pest species. Predation rate was found higher in the no-choice predation because of unavailability of substitutes feeding source. The investigation also indicated each predatory spider killed more pests than consumed. The findings of this study support the predatory role of spiders in controlling the cotton major pests.

Behavioral Studies of the Parasitoid Bracon vulgaris Ashmead (Hymenoptera: Braconidae)

Bracon vulgaris is a larval ectoparasitoid of the boll weevil, Anthonomus grandis, a key cotton pest We investigated the influence of parasitoid age, photoperiod and host availability on B. vulgaris parasitism. Five- and 10-day-old parasitoids were exposed to A. grandis densities of three, six, 12 and 24 larvae per female. Five-day-old females showed higher parasitism rates (F = 21.55, P < 0.0001), with a positive increase in parasitism rate up to 12 larvae, parasitizing an average (±SE) of 1.3 (±0.12), 3.4 (±0.35) and 4.4 (±0.45) larvae (at the densities of 3, 6 and 12 larvae, respectively), dropping to 1.4 (±0.17) when 24 larvae were offered. Next, the period of most parasitism activity during the photophase was determined by exposing five-dayold B. vulgaris females to different durations of light exposure (1, 3, 6, 8 and 10 h) after 12 h darkness. Results showed that the shortest time to host location occurred 8 h after light exposure, when parasitoids were most active searching for the host. A sequence of seven behavioral acts leading to successful parasitism was identified and the transitions between successive behavioral acts were quantified and depicted in an ethogram. The longest duration act was oviposition (or host acceptance), a complex behavior with several distinct phases.

Interaction ofAnthonomus grandisand cotton genotypes: biological and behavioral responses

AbstractThe boll weevil,Anthonomus grandisBoheman (Coleoptera:Curculionidae), is a key pest of cotton,Gossypium hirsutumL. (Malvaceae). Knowledge about boll weevil feeding and oviposition behavior and its response to plant volatiles can underpin our understanding of host plant resistance, and contribute to improved monitoring and mass capture of this pest. Boll weevil oviposition preference and immature development in four cotton genotypes (CNPA TB90,TB85,TB15, andBRSRubi) were investigated in the laboratory and greenhouse. Volatile organic compounds (VOCs) produced byTB90 and Rubi genotypes were obtained from herbivore‐damaged and undamaged control plants at two phenological stages – vegetative (prior to squaring) and reproductive (during squaring) – and four collection times – 24, 48, 72, and 96 h following herbivore damage. The boll weevil exhibited similar feeding and oviposition behavior across the four tested cotton genotypes. The chemical profiles of herbivore‐damaged plants of both genotypes across the two phenological stages were qualitatively similar, but differed in the amount of volatiles produced. Boll weevil response toVOCextracts was studied using a Y‐tube olfactometer. The boll weevil exhibited similar feeding and oviposition behavior at the four tested cotton genotypes, although delayed development and production of smaller adults was found when fedTB85. The chemical profile of herbivore‐damaged plants of both genotypes at the two phenological stages and time periods (24–96 h) was similar qualitatively, with 30 identified compounds, but differed in the amount of volatiles produced. Additionally, boll weevil olfactory response was positive to herbivory‐induced volatiles. The results help to understand the interaction betweenA. grandisand cotton plants, and why it is difficult to obtain cotton genotypes possessing constitutive resistance to this pest.

Influence of the surrounding landscape on crop colonization by a polyphagous insect pest

AbstractLandscape composition plays an important, but poorly understood, role in the population dynamics of agricultural pest species with broad host ranges including both crops and weeds. One such pest, the generalist plant bugLygus hesperusKnight (Hemiptera:Miridae), is a key cotton pest that feeds on various hosts differing in quality inCalifornia'sSanJoaquinValley (USA). We investigated the effects of 15 common crops and uncultivated agricultural land onL. hesperuspopulations, by correlating the densities ofL. hesperusin focal cotton fields with the areas of the 16 crops in surrounding rings. Insect counts were provided by private pest‐control advisors, and spatial data were obtained fromKernCounty records. We first calculatedSpearman's partial correlation coefficients on an annual basis for each crop separately, and then performed a meta‐analysis of these correlations across years to describe the overall effect of a particular crop onL. hesperusafter the effects of the 15 other crops are removed. Consistent with studies conducted in other areas,L. hesperusdensity was positively correlated with safflower, and negatively with cotton.Lygus hesperusdensity was also correlated with several other crops that are often not considered in pest management, including grape, oat, and onion (positive correlations), and almond, pistachio, and potato (negative correlations).Lygus hesperusdensity was also found to be negatively correlated with alfalfa and positively correlated with uncultivated habitats, a relationship that receives mixed support in the literature. Several other crops tested were not significantly correlated withL. hesperusdensities in focal cotton fields, suggesting a neutral role for them inL. hesperusdynamics. The improved understanding of the effects of a greater variety of crops onL. hesperuspopulation dynamics will be useful in the design of agricultural landscapes for enhanced management of this important polyphagous pest.

Effects of Bacillus thuringiensis isolates and single nuclear polyhedrosis virus in combination and alone on Helicoverpa armigera

Cotton bollworm is a key pest of cotton and other crops in many parts of Asia. Evaluation of three native Bacillus thuringiensis isolates and HaSNPV on cotton bollworm was studied. Results revealed that KD-2 isolate was the superior isolate, that its LC50 was 1.2 × 107 spore ml−1 and LC50 of HaSNPV equal to 9.2 × 103 OB ml−1. Interactions on the mortality and debilitating effects between B. thuringiensis KD-2 isolate (3 × 106, 6 × 106, 1.21 × 107 and 1.8 × 107 spore ml−1) and HaSNPV (2.3 × 103, 4.6 × 103 and 9.2 × 103 OB ml−1) on second instars larvae of Helicoverpa armigera were evaluated in laboratory. The larvae of cotton bollworm were fed for 48 h on the treated diets. The results revealed that the Bt at 1.2 × 107 spore ml−1, mixed with all above-mentioned concentrations of HaSNPV, had antagonistic effects. However, the Bt at 1.8 × 107 spore ml−1, mixed with HaSNPV at 9.2 × 103 OB ml−1, had additive effect. The Bt at 6 × 106 spore ml−1 mixed with all above-mentioned concentrations of HaSNPV demonstrated additive effects. The Bt at 3 × 106 spore ml−1 had additive effect with HaNPV at 2.3 × 103 and 4.6 × 103 OB ml−1. The mortality observed in larvae infected with the combination of both Bt (3 × 106 spore ml−1) and HaSNPV (9.2 × 103 OB ml−1) was interpreted as synergist effect. Therefore, it could be concluded that combination of the lowest Bt concentration and the highest HaSNPV concentration had synergist effect on H. armigera second instar larvae.

The control and protection of cotton plants using natural insecticides against the colonization by Aphis gossypii Glover (Hemiptera: Aphididae)

The cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), is a key pest of cotton, irrespective of the use of conventional or organic management. In organic systems, however, the use of synthetic insecticides is not allowed, increasing the difficulty of controlling this pest. This work evaluated aphid control and the ability of products to prevent aphid infestation using natural insecticides compared to a standard synthetic insecticide. The control trial was conducted with four products [Beauveria bassiana (Boveril&amp;reg;), neem oil (Neemseto®), and cotton seed oil compared to thiamethoxam (Actara®)], and untreated plants served as the control group. The trial testing the efficacy of these products in preventing aphid infestation was conducted using the same products, excluding Boveril®. The evaluations were conducted 72 and 120h post-treatment for the efficacy and the protection against colonization trials, respectively. The aphid control by cotton seed oil, Neemseto®, and thiamethoxam was similar, with 100% control being achieved on the thiamethoxam-treated plants. Regarding the plant protection against aphid colonization, the insecticide thiamethoxam exhibited a better performance compared to the other tested products with steady results over the evaluation period. The natural products exhibited variable results with low protection against plant colonization throughout the evaluation period.

Injury to Cotton by Adult &lt;I&gt;Lygus hesperus&lt;/I&gt; (Hemiptera: Miridae) of Different Gender and Reproductive States

Lygus hesperus Knight (Hemiptera: Miridae) is a key pest of cotton (Gossypium spp.) in the western United States that injures floral buds (squares) and developing fruit (bolls). However, no clear relationship between Lygus population level and plant injury has been established. Age-dependent feeding activity by L. hesperus is a possible source of variation that has not been examined for its influence in studies of the impact of Lygus on cotton. Recent video-based laboratory studies indicated that feeding behaviors and trivial movement varied among L. hesperus adults of different gender and reproductive states (prereproductive; reproductive and unmated; and reproductive and mated). We compared within-plant distributions and accumulations of feeding injury to intact cotton plants corresponding to adult L. hesperus of different gender and reproductive states. Adult females, regardless of reproductive state, were observed on squares and axillary buds more often than were males. Additionally, prereproductive adults were observed on squares and axillary buds more often than were mated or unmated reproductive adults, regardless of gender. Plants that were exposed to prereproductive adults exhibited more abscised squares and more squares with injured anthers compared with plants exposed to reproductive adults. However, feeding injury did not differ by insect mating status or gender. These results are consistent with results of our previous video-based assays, and indicate adult reproductive state represents a source of variation that should be controlled in studies to evaluate Lygus-induced injury to cotton and other crop plants.

Insecticide resistance in Brazilian populations of the cotton leaf worm, Alabama argillacea

The cotton leaf worm, Alabama argillacea, is a key cotton pest in Brazil and is managed with repeated insecticide applications. Reports of insecticide control failures have recently increased, particularly with pyrethroids. The present work assessed the resistance status of A. argillacea to a number of different insecticides currently used in cotton crops. Bioassays were conducted to estimate the response of 2nd-instar A. argillacea populations to deltamethrin, chlorpyrifos, endosulfan, abamectin and spinosad. A leaf dip bioassay with diluted insecticide formulations was performed in the laboratory with five to nine populations depending on the insecticide. LC 50 values were estimated by probit analysis after correction for control mortality data and used to calculate the resistance ratios (RR). All assessed populations exhibited varied and significant levels of resistance to all insecticides tested, but only moderate levels of resistance to deltamethrin were observed (RR = 52.3). The LC 50 values for deltamethrin were higher than 30 mg/l for most populations, and above the field rate (12.5 mg/l). This suggests that the frequency of resistant individuals in these populations was likely above the critical frequency. There was low to moderate resistance to abamectin, chlorpyrifos, endosulfan and spinosad formulations (the highest RRs observed were 4.2, 8.4, 11.1 and 23.5, respectively). Despite the moderate levels of resistance to pyrethroids in A. argillacea, overall results indicate the presence of low to moderate resistance of A. argillacea to insecticides currently used against cotton pests in Brazil.

Laboratory Studies of Variations in Feeding Behaviors Among &lt;I&gt;Lygus hesperus&lt;/I&gt; (Hemiptera: Miridae) of Different Gender and Reproductive States

Lygus hesperus Knight (Hemiptera: Miridae) is a key pest of cotton (Gossypium spp.) in the western United States that injures floral buds (squares) and developing fruit (bolls). Levels of Lygus-induced damage to cotton can vary by Lygus ages or gender, and these variations complicate interpretation of studies designed to elucidate Lygus and cotton interactions. Variations in observed injury may reflect different behaviors among Lygus gender or ages. We compared times allocated to feeding and trivial movement between male and female adult L. hesperus of different reproductive states: prereproductive, reproductive and mated, and reproductive and unmated. Prereproductive adults exhibited less trivial movement and spent more time stylet-probing compared with reproductive unmated and mated adults. Mated females stylet-probed more times than other classes of adults, whereas mated and unmated reproductive females exhibited more test probes (≤10 s duration) than prereproductive females. Reproductive females probed the anther region of squares less than prereproductive females. Instead, reproductive females tended to stylet-probe squares below the bracts, which is also where they oviposited. Each oviposition event was preceded by a short duration stylet-probe at the oviposition location. Unmated reproductive males exhibited more test probes but fewer ingestion probes (>1 min) compared with prereproductive and mated males. These results indicate a pattern in which prereproductive adults are less active and feed more compared with reproductive adults, but behaviors vary among reproductive adults of different gender and mating states. We propose that differences in behaviors exhibited among adult L. hesperus are related to the different requirements imposed by mate seeking, mate attraction, and oviposition.

Fourteen Years ofBtCotton Advances IPM in Arizona

The pink bollworm, Pectinophora gossypiella (Saunders), first invaded Arizona in 1926 and has been a key pest of cotton, Gossypium hirsutum L., since the early 1960s. A broad range of tactics has been developed to manage this pest including a variety of cultural methods, mating disruption via pheromones, sterile insect release, and plant resistance. Transgenic cotton producing the insecticidal proteins of Bacillus thuringiensis Berliner (Bt) was introduced in 1996 and was rapidly and widely adopted by producers in Arizona. Adoption rose to approximately 86% by 2006 and has been more than 93% since 2007 when the state was granted a U.S. Environmental Protection Agency exemption to eliminate required refuge plantings as part of a regional eradication program. The deployment of Bt cotton for selective control of caterpillars led to dramatic regional reductions in abundance of pink bollworm, and associated crop damage and insecticide use. Bt cotton has also been a key technology enabling more selective and biologically-based control approaches for sweetpotato whitefly, Bemisia tabaci (Gennadius), and western tarnished plant bug, Lygus hesperus Knight, two other keys pests of cotton in Arizona. Overall insecticide use (statewide average number of sprays per hectare) in cotton has dropped 88% since 1995. Some challenges ahead include re-invasion of eradicated zones, maintaining susceptibility of pink bollworm to Bt cotton, the economics of Bt cotton use in a post-eradication future, and a rapidly changing agroecosystem.

Overwintering hosts of Apolygus lucorum (Hemiptera: Miridae) in northern China

During the past decade, Apolygus lucorum Meyer-Dür (Heteroptera: Miridae) has become a key pest of cotton in northern China, due to widespread planting of Bt cotton and an associated drop in the use of broad-spectrum insecticides. Because of a lack of management alternatives, A. lucorum outbreaks are presently exclusively controlled with insecticides. In this study, we determined A. lucorum overwintering locations and host plants during the 2006–2009 winter seasons. A total of 126 plant species were screened and nymphal emergence of A. lucorum was monitored over time. Eggs of A. lucorum successfully overwintered in cotton field soils and on 86 plant species, including weeds, fruit trees, pastures and agricultural crops. More specifically, Vitis vinifera L., Ricinus communis L., Momordica charantia L., Artemisia argyi Levl. et Vant., Artemisia annua L., Artemisia lavandulaefolia DC., Isatis indigotica Fort., Artemisia scoparia Waldst. et Kit., Vigna radiate (L.) Wilczek, Ziziphus jujuba Mill., Vigna angularis (Willd.) Ohwi et, Ocimum basilicum L., Onobrychi viciifolia Scop., Pyrus bretschneideri Rehd., Malus domestica Borkh. and Brassica juncea (L.) Czern. et Coss proved optimal overwintering hosts of A. lucorum. Based upon plant species occurrence and distribution in Chinese cotton-growing regions, several weeds and fruit trees, such as V. vinifera, Z. jujuba, P. bretschneideri and M. domestica can be termed key overwintering hosts of A. lucorum. Our findings can form the basis for future formulation of targeted management actions to lower A. lucorum overwintering populations in cotton-growing landscapes of northern China.

Electrophysiological and Behavioral Responses ofMicroplitis mediator(Hymenoptera: Braconidae) to Caterpillar-Induced Volatiles From Cotton

Microplitis mediator Haliday (Hymenoptera: Braconidae) is an important larval endoparasitoid of various lepidopteran pests, including Helicoverpa armigera (Hübner). In China, H. armigera is a key pest of cotton and is currently the focus of several biological control efforts that use M. mediator as principal natural enemy of this pest. To improve the success of biological control efforts, behavioral studies are needed that shed light on the interaction between M. mediator and H. armigera. In this study, we determined M. mediator response to volatile compounds from undamaged, mechanically injured, or H. armigera--damaged plants and identified attractive volatiles. In Y-tube olfactometer assays, we found that mechanically damaged plants and/or plants treated with H. armigera oral secretions did not attract wasps. However, volatiles from H. armigera-damaged plants elicited a strong attraction of both M. mediator sexes. Headspace extracts from H. armigera-damaged cotton were analyzed by coupled gas chromatography-electroantennographic detection (GC-EAD), and a total of seven different compounds were found to elicit electroantennogram (EAG) responses, including an unknown compound. Six different EAD-active volatiles were identified from caterpillar-damaged cotton plants, of which 3, 7-dimethyl-1, 3, 6-octatriene and (Z)-3-hexenyl acetate were the principal compounds. Olfactometer assays indicated that individual synthetic compounds of 3, 7-dimethyl-1, 3, 6-octatriene, (Z)-3-hexenyl acetate, and nonanal were attractive to M. mediator. Field cage studies showed that parasitism of H. armigera larvae by M. mediator was higher on cotton plants to which 3,7-dimethyl-1,3, 6-octatriene was applied. Our results show that the combination of terpenoids and green leaf volatiles may not only facilitate host, mate, or food location but may also increase H. armigera parasitism by M. mediator.

Monitoring resistance of Helicoverpa armigera to different insecticides used in cotton in Spain

Helicoverpa armigera is the key pest of cotton in Spain, resulting in many insecticide treatments against it. The resistance status of H. armigera to different insecticides currently used in cotton was evaluated in Spain in two different seasons, 1999 and 2004. Four populations were tested in total, two in each season. Toxicological bioassays were conducted in the laboratory, and performed on third instar larvae by topical application of the insecticides. LD 50's were estimated by probit analysis and resistance factors (RF) were calculated at the LD 50 level. Four insecticides were evaluated, but only endosulfan reached a moderate resistance level (RF = 11.4), and the others (methomyl, chlorpyrifos and lambda-cyhalothrin) showed low resistance (RF between 1.9 and 6.0). Such results indicate the generally low resistance of H. armigera to most of the insecticides used against this pest in cotton in Spain. Possible explanations for this situation are discussed.

Asymmetrical cross-resistance betweenBacillus thuringiensistoxins Cry1Ac and Cry2Ab in pink bollworm

Transgenic crops producing Bacillus thuringiensis (Bt) toxins kill some key insect pests and can reduce reliance on insecticide sprays. Sustainable use of such crops requires methods for delaying evolution of resistance by pests. To thwart pest resistance, some transgenic crops produce 2 different Bt toxins targeting the same pest. This "pyramid" strategy is expected to work best when selection for resistance to 1 toxin does not cause cross-resistance to the other toxin. The most widely used pyramid is transgenic cotton producing Bt toxins Cry1Ac and Cry2Ab. Cross-resistance between these toxins was presumed unlikely because they bind to different larval midgut target sites. Previous results showed that laboratory selection with Cry1Ac caused little or no cross-resistance to Cry2A toxins in pink bollworm (Pectinophora gossypiella), a major cotton pest. We show here, however, that laboratory selection of pink bollworm with Cry2Ab caused up to 420-fold cross-resistance to Cry1Ac as well as 240-fold resistance to Cry2Ab. Inheritance of resistance to high concentrations of Cry2Ab was recessive. Larvae from a laboratory strain resistant to Cry1Ac and Cry2Ab in diet bioassays survived on cotton bolls producing only Cry1Ac, but not on cotton bolls producing both toxins. Thus, the asymmetrical cross-resistance seen here does not threaten the efficacy of pyramided Bt cotton against pink bollworm. Nonetheless, the results here and previous evidence indicate that cross-resistance occurs between Cry1Ac and Cry2Ab in some key cotton pests. Incorporating the potential effects of such cross-resistance in resistance management plans may help to sustain the efficacy of pyramided Bt crops.

Morphology and Histology of the Alimentary Canal of &lt;I&gt;Lygus hesperus&lt;/I&gt; (Heteroptera: Cimicomoropha: Miridae)

Abstract Microdissection and transverse semithin sections were used to perform a light microscopy survey of the gross morphology and cellular anatomy of the alimentary canal, respectively, of Lygus hesperus Knight, a key pest of cotton (Gossypium hirsutum L.), alfalfa (Medicago sativa L.), and other crops. The gross morphology of the alimentary canal showed a relatively unadorned tube compared with other hemipterans, with variably shaped compartments and one small diverticulum. However, the epithelial cell anatomy of the gut was relatively complex, with the midgut having the most diverse structure and cell types. The midgut was typical of the “Lygus-type gut” seen in the older literature, i.e., it consisted of three major regions, the first (descending), second (ascending), and third (descending) ventriculi, with different variants of three major epithelial cell types in each region. Our light microscopy (LM) study suggests that the three cell types are nondifferentiated regenerative cells (which sparsely...

Detection and Evolution of Resistance to the Pyrethroid Cypermethrin in &lt;I&gt;Helicoverpa zea&lt;/I&gt; (Lepidoptera: Noctuidae) Populations in Texas

The bollworm, Helicoverpa zea (Boddie), is a key pest of cotton in Texas. Bollworm populations are widely controlled with pyrethroid insecticides in cotton and exposed to pyrethroids in other major crops such as grain sorghum, corn, and soybeans. A statewide program that evaluated cypermethrin resistance in male bollworm populations using an adult vial test was conducted from 2003 to 2006 in the major cotton production regions of Texas. Estimated parameters from the most susceptible field population currently available (Burleson County, September 2005) were used to calculate resistance ratios and their statistical significance. Populations from several counties had statistically significant (P < or = 0.05) resistance ratios for the LC(50), indicating that bollworm-resistant populations are widespread in Texas. The highest resistance ratios for the LC(50) were observed for populations in Burleson County in 2000 and 2003, Nueces County in 2004, and Williamson and Uvalde Counties in 2005. These findings explain the observed pyrethroid control failures in various counties in Texas. Based on the assumption that resistance is caused by a single gene, the Hardy-Weinberg equilibrium formula was used for estimation of frequencies for the putative resistant allele (q) using 3 and 10 microg/vial as discriminatory dosages for susceptible and heterozygote resistant insects, respectively. The influence of migration on local levels of resistance was estimated by analysis of wind trajectories, which partially clarifies the rapid evolution of resistance to cypermethrin in bollworm populations. This approach could be used in evaluating resistance evolution in other migratory pests.

Insect resistance management for Syngenta’s VipCot™ transgenic cotton

Syngenta is seeking commercial registration for VipCot™ cotton, a pyramided transgenic cotton trait that expresses two insecticidal proteins derived from Bacillus thuringiensis Vip3A and Cry1Ab. Both proteins are highly effective against two key cotton pests, Helicoverpa zea cotton bollworm; and Heliothis virescens, tobacco budworm. To investigate the role of VipCot™ cotton in delaying the development of resistance in these pests to transgenic Bt traits, Syngenta has performed studies to determine the dose of proteins expressed in VipCot™ and evaluate the potential for cross-resistance between the component proteins. Following United States Environmental Protection Agency (US EPA) high dose methods 1 and 4, VipCot™ was shown to express a high dose of proteins for H. zea and H. virescens. VipCot™ was also confirmed to express a high dose of proteins for H. zea through US EPA Method 5. Additionally, all the data collected to date verify a lack of cross-resistance between Vip3A and Cry proteins. These two key pieces of information indicate that VipCot™ cotton should be very durable under the currently mandated high dose plus refuge insect resistance management strategy.

Selective Feeding of Tobacco Budworm and Bollworm (Lepidoptera: Noctuidae) on Meridic Diet with Different Concentrations of &lt;I&gt;Bacillus thuringiensis&lt;/I&gt; Proteins

Laboratory experiments were conducted to evaluate the behavior of bollworm, Helicoverpa zea (Boddie), and tobacco budworm, Heliothis virescens (F.), larvae on meridic diet with different concentrations of the Cry1Ac and Cry2Ab proteins from Bacillus thuringiensis subsp. kurstaki Berliner. The proteins used in these experiments are the ones in commercially available Bollgard and Bollgard II cotton. Both bollworms and tobacco budworms selectively fed on nontreated diet compared with diet treated with Cry1Ac. In addition, bollworms exhibited a concentration response with Cry1Ac. In general, bollworms selected diet with low concentrations of Cry1Ac compared with diet with higher concentrations of Cry1Ac. For Cry2Ab, the avoidance was not as prominent as that observed for Cry1Ac. Based on results from no-choice assays, the Cry1Ac and Cry2Ab concentrations used in choice assays represented a wide range of biological activity on both species. The lower concentrations provided low levels of mortality, whereas the higher concentrations provided high levels of mortality. Also, the developmental times of larvae were longer at higher concentrations of both proteins. These data provide important information about the behavioral response of key cotton pests to the B. thuringiensis proteins found in commercially available transgenic cotton. This information will be important to develop accurate scouting and management procedures for Bollgard and Bollgard II cotton.

Omnivore or Herbivore? Field Observations of Foraging byLygus hesperus(Hemiptera: Miridae)

When important agricultural pests are omnivores instead of strict herbivores, their impact on the host plant may change as the omnivore shifts between consumption of plants and consumption of prey. Lygus hesperus, a key pest of cotton, is known from laboratory and field studies to be an omnivore, but no field studies have ever quantified the importance of predation as a source of food. Cotton growers have long considered the impact of L. hesperus on cotton to be enigmatic, because sometimes crop damage seems to be higher or lower than would be expected based upon the density of L. hesperus estimated through sweep net samples. Here, we conducted focal observations of L. hesperus foraging freely in the field to quantify the relative importance of predation versus herbivory as food resources and to determine whether omnivory was sufficiently common that it might underlie the “Lygus enigma.” In observations of 84 individuals over a total of 56.7 h, we did not observe any predation events. Observations conducted in the laboratory under continuous magnification also yielded no evidence of predation, suggesting that we were not failing to detect predation events on small or cryptic prey in the field. Thus, L. hesperus expresses predatory behavior at most very infrequently and develops essentially as an herbivore in California cotton. We did, however, find that adult male L. hesperus spend more of their time resting and spend less time on the vulnerable reproductive structures of the cotton plant compared with nymphal stages or adult females. Further work on the Lygus enigma will examine the differential ease of sampling different L. hesperus life stages and the possibility that they contribute unequally to crop damage.

Tethered and Untethered Flight byLygus hesperusandLygus lineolaris(Heteroptera: Miridae)

When important agricultural pests are omnivores instead of strict herbivores, their impact on the host plant may change as the omnivore shifts between consumption of plants and consumption of prey. Lygus hesperus, a key pest of cotton, is known from laboratory and field studies to be an omnivore, but no field studies have ever quantified the importance of predation as a source of food. Cotton growers have long considered the impact of L. hesperus on cotton to be enigmatic, because sometimes crop damage seems to be higher or lower than would be expected based upon the density of L. hesperus estimated through sweep net samples. Here, we conducted focal observations of L. hesperus foraging freely in the field to quantify the relative importance of predation versus herbivory as food resources and to determine whether omnivory was sufficiently common that it might underlie the “Lygus enigma.” In observations of 84 individuals over a total of 56.7 h, we did not observe any predation events. Observations conducted in the laboratory under continuous magnification also yielded no evidence of predation, suggesting that we were not failing to detect predation events on small or cryptic prey in the field. Thus, L. hesperus expresses predatory behavior at most very infrequently and develops essentially as an herbivore in California cotton. We did, however, find that adult male L. hesperus spend more of their time resting and spend less time on the vulnerable reproductive structures of the cotton plant compared with nymphal stages or adult females. Further work on the Lygus enigma will examine the differential ease of sampling different L. hesperus life stages and the possibility that they contribute unequally to crop damage.