Expression of Bacillus thuringiensis Cry1Ac protein in cotton plants, acquisition by pests and predators: a tritrophic analysis

1. Studies have shown that Cry proteins of the bacterium Bacillus thuringiensis expressed in transgenic plants can be acquired by nontarget herbivores and predators. A series of studies under field and controlled conditions was conducted to investigate the extent to which Cry1Ac protein from Bt transgenic cotton reaches the third trophic level and to measure the amount of protein that herbivores can acquire and expose to predators. 2. Levels of Cry1Ac in Bt cotton leaves decreased over the season. Among herbivores (four species), Cry1Ac was detected in lepidopteran larvae and the amount varied between species. Among predators (seven species), Cry1Ac was detected in Podisus maculiventris and Chrysoperla rufilabris. 3. In the greenhouse, only 14% of the Cry1Ac detected in the prey (Spodoptera exigua larvae) was subsequently found in the predator P. maculiventris. Detection of Cry1Ac protein in Orius insidiosus, Geocoris punctipes and Nabis roseipennis was probably limited by the amount of prey consumed that had fed on Bt cotton. 4. Purified Cry1Ac was acquired by the small predatory bug G. punctipes but at much higher concentration than found in plants or in lepidopteran larvae. 5. Bt protein was shown to move through prey to the third trophic level. Predatory heteropterans acquired Cry1Ac from prey fed Bt cotton, but acquisition was dependent on the concentration of Cry1Ac conveyed by the prey and the amount of prey consumed. The type and availability of prey capable of acquiring the protein, coupled with the generalist feeding behaviour of the most common predators in the cotton ecosystem, probably constrain the flow of Cry1Ac through trophic levels.     

Phylogenetic position and composition of Zygiellinae and Caerostris,with new insight into orb‐web evolution and gigantism

Orb‐weaving spiders are good objects for evolutionary research, but phylogenetic relationships among and within orb‐weaving lineages are poorly understood. Here we present the first species‐level molecular phylogeny that includes the enigmatic orb weavers ‘Zygiellidae’ and Caerostris. Zygiellidae is interesting for the evolution of the sector web, and Caerostris is noteworthy for web gigantism and extraordinary silk biomechanics. We assembled a molecular data set using mitochondrial (COI, 16S) and nuclear (H3, 18S, 28S, ITS2) gene fragments for 112 orbicularian exemplars, focusing on taxa with diverse web architecture and size. We show that ‘Zygiellidae’ contains the Holarctic Zygiella genus group (Leviellus, Parazygiella, Stroemiellus, and Zygiella) and the Australasian Phonognatha and Deliochus. As this clade is placed with Araneidae in all analyses we treat it as a subfamily, Zygiellinae. Using the new phylogeny, we show that the sector web evolved eight times, and coevolved with the silk tube retreat, but that these features are not zygielline synapomorphies. Zygiellinae, Caerostris, and some other araneids form a basal grade of araneids that differ from ‘classical’ araneids in web‐building and preying behaviour. We also confirm that Caerostris represents the most striking case of spider‐web gigantism. © 2015 The Linnean Society of London     

Seasonal variation in seed predation by adult carabid beetles

In many agro‐ecosystems of the temperate region, granivorous ground beetles (Coleoptera: Carabidae) are the most important invertebrate predators of seeds after dispersal. The consumption of a particular species of seed differs among carabid species, but seasonal variation in consumption has not yet been studied. Seasonal differences in the quantity of seed consumed by the carabids Harpalus affinis (Schrank) and Harpalus distinguendus (Duftschmid) were studied in a cafeteria experiment. Adults were collected on five dates between April and November and provided with seeds of 28 species of dicotyledonous herbaceous plants. Proportions eaten of the seeds offered (preferences) were nearly identical in both carabid species. Overall seed consumption increased from early spring until late June, then gradually decreased towards autumn. Despite this variation, the preferences on particular dates were essentially similar. Seasonal variation in carabid physiology and feeding experience thus influenced overall seed consumption, but not their preferences for particular seed species.     

Effects of elevated CO2 on the interspecific competition between two sympatric species of Aphis gossypii and Bemisia tabaci fed on transgenic Bt cotton

Abstract Effects of elevated CO₂ (twice ambient vs. ambient) and Bt Cry1Ac transgene (Bt cotton cv. 33^B vs. its nontransgenic parental line cv. DP5415) on the interspecific competition between two ecologically similar species of cotton aphid Aphis gossypii and whitefly biotype‐Q Bemisia tabaci were studied in open‐top chambers. The results indicated that elevated CO₂ and Bt cotton both affected the population abundances of A. gossypii and biotype‐Q B. tabaci when introduced solely (i.e., without interspecific competition) or two species coexisted (i.e., with interspecific competition). Compared with ambient CO₂, elevated CO₂ increased the population abundances of A. gossypii and biotype‐Q B. tabaci as fed on Bt and nontransgenic cotton on 45 (i.e., seedling stage) and 60 (i.e., flowering stage) days after planting (DAP), but only significantly enhanced aphid abundance without interspecific competition on the 45‐DAP nontransgenic cotton and 60‐DAP Bt cotton, and significantly increased whitefly abundance with interspecific competition on the 45‐DAP Bt cotton and 60‐DAP nontransgenic cotton. In addition, compared with nontransgenic cotton at elevated CO₂, Bt cotton significantly reduced biotype‐Q B. tabaci abundances without and with interspecific competition during seedling and flowering stage, while only significantly decreasing A. gossypii abundances without interspecific competition during the seedling stage. When the two insect species coexisted, the proportions of biotype‐Q B. tabaci were significantly higher than those of A. gossypii on Bt and nontransgenic cotton at the same CO₂ levels, and elevated CO₂ only significantly increased the percentages of biotype‐Q B. tabaci and significantly reduced the proportions of A. gossypii on seedling and flowering nontransgenic cotton. Therefore, the effects of elevated CO₂ were favorable for biotype‐Q B. tabaci to out‐compete A. gossypii under the predicted global climate change.     

Feeding of fall armyworm,Spodoptera frugiperda,on Bt transgenic cotton and its isoline

Studies on insect food intake and utilization are important for determining the degree of insect/plant association and host species’ resistance, and also for helping design pest management programs by providing estimates of potential economic losses, techniques for mass breeding of insects, and identifying physiological differences between species. We studied the feeding and development of fall armyworm, Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae), on transgenic (Bt) and non‐transgenic (non‐Bt) cotton. The larvae of S. frugiperda fed on Bt cotton had a longer development period (23.0 days) than those fed on non‐Bt cotton (20.2 days). Survivorship of S. frugiperda larvae fed on Bt cotton (74.1%) was lower than that of larvae fed on non‐Bt cotton (96.7%). Pupal weight of larvae fed on Bt cotton (0.042 g) was lower than that of larvae fed on non‐Bt cotton (0.061 g). The cotton cultivar significantly affected food intake, feces production, metabolization, and food assimilation by S. frugiperda larvae. However, it did not affect their weight gain. Intake of Bt‐cotton leaf (0.53 g dry weight) per S. frugiperda larva was lower than the intake of non‐Bt‐cotton leaf (0.61 g dry weight). Larvae fed on Bt‐cotton leaves produced less feces (0.25 g dry weight) than those fed on non‐Bt‐cotton leaves (0.37 g dry weight). Weight gain per S. frugiperda larva fed on Bt‐cotton leaves (0.058 g dry weight) was similar to the weight gain for larvae fed on non‐Bt‐cotton leaves (0.056 g dry weight). The cotton cultivar significantly affected the relative growth, consumption, and metabolic rates, as well as other nutritional indices: the figures were lower for larvae fed on Bt‐cotton leaves than for larvae fed on non‐transgenic cotton leaves.     

Colonization preference of Euschistus servus and Nezara viridula in transgenic cotton varieties,peanut, and soybean

Producers of Bt cotton, Gossypium hirsutum L. (Malvaceae), in the southeastern USA face significant losses from highly polyphagous stink bug species. These problems may be exacerbated by crop rotation practices that often result in cotton, peanut, Arachis hypogaea L., and soybean, Glycine max (L.) Merrill (both Fabaceae), growing in close proximity to one another. Because all of these crops are hosts for the major pest stink bug species in the region, we experimentally examined colonization preference of these species among the crops to clarify this aspect of their population dynamics. We planted peanut, soybean, Bt cotton, and glyphosate‐tolerant (RR) non‐Bt cotton at three sites over 3 years in replicated plots ranging from 192 to 1 323 m² and calculated odds ratios for colonization of each crop for Nezara viridula (L.) and Euschistus servus (Say) (both Hemiptera: Pentatomidae). In four of five experiments, both E. servus and N. viridula preferred soybean significantly more often than Bt cotton, non‐Bt cotton, and peanut. Neither N. viridula nor E. servus showed any preference between non‐Bt and Bt cotton in any experiment. Both species had higher numbers in Bt and non‐Bt cotton relative to peanut; this was not significant for any single experiment, but analyses across all experiments indicated that N. viridula preferred Bt and non‐Bt cotton significantly more often than peanut. Our results suggest that soybean in the landscape may function as a sink for stink bug populations relative to nearby peanut and cotton when the soybean is in the reproductive stage of development. Stink bug preference for soybean may reduce pest pressure in near‐by crops, but population increases in soybean could lead to this crop functioning as a source for later‐season pest pressure in cotton.     

Influence of within‐field position and adjoining habitat on carabid beetle assemblages in winter wheat

• 1 The influence of within‐field position and adjoining habitat on carabid beetles was studied in 20 winter wheat fields in ten different Swiss agricultural landscapes. In each landscape, two winter wheat fields (one with adjoining sown wildflower area and one with adjoining grassy margin) were investigated.
• 2 Carabid beetles were caught in pitfall traps 3 and 30 m from the edge in each of the 20 wheat fields. Significantly more individuals were found in the centres (30‐m position) than at the edges (3‐m position). Conversely, species richness was significantly higher at the field edges than in the centres.
• 3 Of the ten most abundant species, Poecilus cupreus, Agonum muelleri and Pterostichus melanarius were significantly more abundant in the field centres than at the edges. Harpalus rufipes was significantly more abundant in the fields adjoining sown wildflower areas than in the fields adjoining grassy margins.
• 4 In conclusion, the response of carabid beetles to within‐field position and adjoining habitats was species specific. This needs to be taken into account in habitat management for biodiversity conservation and pest control.

     

Weed seed availability,carabid intraspecific interference and their interaction drive weed seed consumption by carabid beetles

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Effects of different field management systems on the carabid coenosis in oil seed rape with special respect to ecology and nutritional status of predacious Poecilus cupreus L. (Col., Carabidae)

It could be shown, that the differences between two carabid populations on rape fields under intensive management and reduced management (50% N‐input, no insecticide application) were not as striking as one might expect. Despite the fact that total individual numbers of the carabid populations, total species numbers, and number of dominant species were clearly higher in the field under reduced management, RENKONEN ’s R_e showed only a slight difference between the fields with nearly three‐quarter correspondence in dominance structure. The presence of five more carabid species on the field under reduced management is underlined by the low values of JACCARD ’s species identity and WAINSTEIN ’s K_w index of similarity. On the other hand, according to SHANNON ‐WEAVER ’s H_s for species diversity and SHANNON ’s E_s for evenness, the differences between the fields are minor. Even if only the dominant species were taken into account, the similarity between both fields was obvious, despite the fact that in the field under reduced management two more dominant carabid species were found. In both fields, phytophagous Amara similata was the most abundant species. Nevertheless, a special oil seed rape carabid coenosis seems to exist as well, as one was found for cereal crops and for root crops, which might consist of A. similata, Amara aenea, Harpalus affinis, Poecilus cupreus, Pseudophonus rufipes, and Pterostichus melanarius. For P. cupreus, which was chosen as a typically predacious and beneficial carabid species in oil seed rape, biomass, fecundity and determination of the degree of gut filling also showed no differences for the fields. Even the length of elytrae as an indicator for nutritional situation in the preceding year showed no difference. Only the phenology of P. cupreus showed an obvious shift of the peak in activity‐density in the intensively managed field, to a later date in the season, compared with the field under reduced management. The latter reflects the usual spring peak. No sufficient explanation was found for the peak 4 weeks later on the intensively managed field. It can be assumed that a less sufficient food supply (higher numbers of potential food, e.g. larvae of Meligethes spp. in the field under reduced management), due to insecticide input, or long‐term biocide impact on P. cupreus, or a faster growth of rape plants due to high nitrogen input resulting in a less favourable microclimate on the intensively managed field, was responsible for this later peak in activity‐density. To conclude, the relations between the predacious carabids, their potential prey, and the abiotic factors in the habitats seem to be much more complicated than assumed. There is a strong hint that the impact of single parameters such as field management influencing the phenology change obviously over the carabids activity period.     

Carabid beetle assemblage under diversified agroecosystems

Corn (Zea mays L.) and soybean (Glycine max Merrill) were planted in monoculture and strip-intercropping plots (18.3×15.5 m each) under conventional tillage and no-tillage to create differences in habitat structure. The effects of these agronomic practices on carabid beetle species composition were measured by pitfall-trap collections during three years. Although neither the number of individuals or number of species were significantly affected by treatments, analyses of variance indicated that four of the six dominant species (75.7% of the total number of carabids captured in three years) responded to tillage treatments.Harpalus pensylvanicus DeGeer andCyclotrachelus sodalis (LeConte) were more abundant in no-tillage plots, whereasPterostichus chalcites Say andScarites substriatus Haldeman were more common in conventional tillage plots.Pterostichus chalcites was also significantly more abundant in soybean plots than in intercropping or corn plots.H. pensylvanicus, a primarily herbivorous carabid, was the most common species collected. However,P. chalcites, a predaceous carabid, was the dominant species in soybean/conventional tillage plots. The results suggest that characteristics of individual species should be carefully considered for studies of communities such as carabid beetles, which have few strongly dominant species and a wide range of resource utilization.     

Effects of transgenic Bt cotton on insecticide use and abundance of two generalist predators

Considerable effort has been expended to determine if crops genetically engineered to produce Bacillus thuringiensis (Bt) toxins harm non‐target arthropods. However, if Bt crops kill target pests and thereby reduce insecticide use, this could benefit some non‐target arthropods. We analyzed data from 21 commercial cotton fields in Arizona to test the effects of Bt cotton on insecticide use and abundance of two non‐target arthropods, the generalist predators Chrysoperla carnea Stephens (Neuroptera: Chrysopidae) and Orius tristicolor (White) (Heteroptera: Anthocoridae). The number of insecticide sprays was more than double for non‐Bt cotton compared with Bt cotton that produced Cry1Ac. The abundance of both predators was negatively associated with the number of insecticide sprays, although significantly so for only one of two sampling periods for each species tested. With the effects of insecticides statistically removed, field type (Bt or non‐Bt cotton) did not affect the abundance of either predator. Accordingly, without adjusting for the effects of insecticide sprays, the abundance of C. carnea was higher in Bt cotton fields than in non‐Bt cotton fields, but significantly so during only one of two sampling periods. The abundance of O. tristicolor did not differ between field types, even without adjusting for effects of insecticide sprays. The results indicate that Bt crops can affect insecticide use, which in turn can affect the relative abundance of non‐target arthropods in Bt and non‐Bt fields. Thus, environmental impact assessment should incorporate analysis of the effects of transgenic crops on management practices, as well as evaluation of the direct effects of such crops.     

Response of multiple generations of beet armyworm,Spodoptera exigua (Hübner), feeding on transgenic Bt cotton

Development, reproduction and food utilization of three successive generations of beet armyworm, Spodoptera exigua (Hübner), fed on transgenic and non‐transgenic Bt cotton were examined. Significantly longer larval life‐span and lower pupal weight were observed in three successive generations of S. exigua fed on transgenic Bt cotton compared with non‐transgenic Bt cotton. Significantly higher survival rate and adult fecundity of S. exigua were found in three successive generations of S. exigua fed on transgenic Bt cotton compared with non‐transgenic Bt cotton. The survival rate and adult fecundity of S. exigua were occurred significant increase in the third generation compared with the first generation after feeding on transgenic Bt cotton. Significantly lower consumption, frass and relative growth rate (RGR) were observed in three successive generations of S. exigua fed on transgenic Bt cotton compared with non‐transgenic Bt cotton. Cotton variety significantly affected all indices of larval consumption and utilization in three successive generations of S. exigua, except for efficiency of conversion of ingested food. However, beet armyworm generation only significantly affected RGR of S. exigua. The results of this study indicated food quality on the diet‐utilization efficiency of S. exigua was different along with beet armyworm generation. Measuring multigenerational development and food utilization of S. exigua at individual and population level in response to Bacillus thuringiensis (Bt) can provide a more meaningful evaluation of long‐term population dynamics than experiments on a single generation. It is imperative to develop an appropriate multigenerational pest management tactic to monitor the field population dynamics of non‐target pests (e.g., beet armyworm) in agricultural Bt cotton ecosystem.     

Oviposition and feeding avoidance in Helicoverpa armigera (Hübner) against transgenic Bt cotton

Helicoverpa armigera (Hübner), the major target pest of transgenic Bacillus thuringiensis (Bt) cotton, remains susceptible to Bt cotton in China at present. Behavioural avoidance by ovipositing females might lead to reduced exposure to Bt cotton and minimize selection for physiological resistance. We examined the behavioural responses of H. armigera to Bt and non‐Bt cottons to determine whether behavioural avoidance to Bt cotton may be present. In oviposition choice tests, the number of eggs on non‐Bt cotton plants was significantly higher than on Bt cotton plants. Similarly, in no‐choice tests, Bt cotton plants attracted significantly fewer eggs compared with non‐Bt cotton plants. H. armigera neonates showed higher dispersal and lower establishment on Bt cotton than on non‐Bt cotton. First instars were found to feed consistently on non‐Bt cotton leaves, creating large feeding holes, but only produced tiny feeding holes on Bt cotton leaves. The H. armigera population used in this study showed avoidance of oviposition and feeding on Bt cotton. Our results provide important insights into one possible mechanism underlying the durability of Bt cotton resistance and may be useful for improving strategies to sustain the effectiveness of Bt crops.     

Interactions of <Emphasis Type="Italic">Bacillus thuringiensis</Emphasis> Cry1Ac toxin in genetically engineered cotton with predatory heteropterans

A number of cotton varieties have been genetically transformed with genes from Bacillus thuringiensis (Bt) to continuously produce Bt endotoxins, offering whole plant and season-long protection against many lepidopteran larvae. Constant whole-plant toxin expression creates a significant opportunity for non-target herbivores to acquire and bio-accumulate the toxin for higher trophic levels. In the present study we investigated movement of Cry1Ac toxin from the transgenic cotton plant through specific predator-prey pairings, using omnivorous predators with common cotton pests as prey: (1) the beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae), with the predator Podisus maculiventris (Heteroptera: Pentatomidae); (2) the two-spotted spider mite, Tetranychus urticae (Acarina: Tetranychidae), with the predatory big-eyed bug Geocoris punctipes (Heteroptera: Geocoridae) and (3) with the predatory damsel bug Nabis roseipennis (Heteropera: Nabidae); and (4) the thrips Frankliniella occidentalis (Thysanoptera: Thripidae) with the predatory pirate bug Orius insidiosus (Heteroptera: Anthocoridae). We quantified Cry1Ac toxin in the cotton plants, and in the pests and predators, and the effects of continuous feeding on S. exigua larvae fed either Bt or non-Bt cotton on life history traits of P. maculiventris. All three herbivores were able to convey Cry1Ac toxin to their respective predators. Among the herbivores, T. urticae exhibited 16.8 times more toxin in their bodies than that expressed in Bt-cotton plant, followed by S. exigua (1.05 times), and F. occidentalis immatures and adults (0.63 and 0.73 times, respectively). Of the toxin in the respective herbivorous prey, 4, 40, 17 and 14% of that amount was measured in the predators G. punctipes, P. maculiventris, O. insidiosus, and N. roseipennis, respectively. The predator P. maculiventris exhibited similar life history characteristics (developmental time, survival, longevity, and fecundity) regardless of the prey’s food source. Thus, Cry1Ac toxin is conveyed through non-target herbivores to natural enemies at different levels depending on the herbivore species, but continuous lifetime contact with the toxin by the predator P. maculiventris through its prey had no effect on the predator’s life history. The results found here, supplemented with others already published, suggest that feeding on Cry1Ac contaminated non-target herbivores does not harm predatory heteropterans and, therefore, cultivation of Bt cotton may provide an opportunity for conservation of these predators in cotton ecosystems by reducing insecticide use.     

Stay or move: how Bt‐susceptible Helicoverpa armigera neonates behave on Bt cotton plants

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) larvae occasionally have been reported to survive at management threshold levels in fields of Bollgard II^® cotton, Gossypium hirsutum L. (Malvaceae). The pattern and degree of larval survival is not easily predicted but depends on the ability of first instars to establish on host plants. Experiments were conducted with Bacillus thuringiensis Berliner (Bt)‐susceptible and Bt‐resistant larvae of H. armigera to understand how physiologically Bt‐susceptible H. armigera survive on Bt cotton plants, and examine how their first meal influences survival rates. In assays using cotton plant parts, both strains of larvae displayed similar tendencies to drop‐off specific plant parts of Bt and non‐Bt cotton. However, significantly more Bt‐susceptible larvae dropped off young leaves, mature leaves, and squares of Bt cotton compared to non‐Bt cotton plants. Egg cannibalism significantly improved the survival of Bt‐susceptible H. armigera larvae on Bt cotton plants. Larvae were more likely to eat live aged eggs, than newly laid or dead eggs. Survival significantly improved when larvae cannibalized eggs before feeding on Bt leaves. The behavior of Bt‐susceptible larvae with respect to drop‐off and egg cannibalism may help enhance their survival on Bt cotton plants.     

Next‐generation transgenic cotton: pyramiding RNAi and Bt counters insect resistance

Transgenic crops producing insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) are extensively cultivated worldwide. To counter rapidly increasing pest resistance to crops that produce single Bt toxins, transgenic plant ‘pyramids’ producing two or more Bt toxins that kill the same pest have been widely adopted. However, cross‐resistance and antagonism between Bt toxins limit the sustainability of this approach. Here we describe development and testing of the first pyramids of cotton combining protection from a Bt toxin and RNA interference (RNAi). We developed two types of transgenic cotton plants producing double‐stranded RNA (dsRNA) from the global lepidopteran pest Helicoverpa armigera designed to interfere with its metabolism of juvenile hormone (JH). We focused on suppression of JH acid methyltransferase (JHAMT), which is crucial for JH synthesis, and JH‐binding protein (JHBP), which transports JH to organs. In 2015 and 2016, we tested larvae from a Bt‐resistant strain and a related susceptible strain of H. armigera on seven types of cotton: two controls, Bt cotton, two types of RNAi cotton (targeting JHAMT or JHBP) and two pyramids (Bt cotton plus each type of RNAi). Both types of RNAi cotton were effective against Bt‐resistant insects. Bt cotton and RNAi acted independently against the susceptible strain. In computer simulations of conditions in northern China, where millions of farmers grow Bt cotton as well as abundant non‐transgenic host plants of H. armigera, pyramided cotton combining a Bt toxin and RNAi substantially delayed resistance relative to using Bt cotton alone.     

Differences between ecological niches in northern and southern populations of Angolan black and white colobus monkeys (Colobus angolensis palliatus and Colobus angolensis sharpei) throughout Kenya and Tanzania

Ecological niche models can be useful for clarifying relationships between environmental factors and a species’ geographic distribution. In this study, we use presence‐only data and environmental layers to create an ecological niche model to better understand the distribution of the East African Angolan black and white colobus monkey, Colobus angolensis palliatus, and to assess whether the model supports considering the population as two separate subspecies, Colobus angolensis sharpei and C. a. palliatus. We found the range of the predicted distribution for suitable habitat of C. a. palliatus as currently classified to be only 12.4% of that shown in the International Union for Conservation of Nature Red List range map and to be fragmented. As C. angolensis is considered a “Least Concern” species, this difference suggests that generalized maps may lead to understating the species’ extinction risk. When presence points were divided into two previously proposed subspecies —C. a. palliatus (Kenya and Northern Tanzania) and C. a. sharpei (Southern Tanzania)—we found significant environmental differences between the distributions. The most important ecological variable for C. a. palliatus was predominantly precipitation of the driest month (69.1%) whereas for C. a. sharpei annual precipitation (44.8%) and land cover (normalized difference vegetation index, 16.4%) were the most important. When comparing suitable ranges for the separate distributions, we found only a 1.2% geographical overlap. These differences are consistent with previous subspecies delineations of C. a. palliatus and C. a. sharpei based upon morphology, pelage, and genetics. Our study suggests that extirpation of C. a. palliatus in suitable habitat areas and occurrence of this subspecies in anthropogenic environments, warrant further consideration for conservation actions.     

Regional assessment of Helicoverpa zea populations on cotton and non-cotton crop hosts

Selection pressure on bollworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), by cotton, Gossypium hirsutum (L.) (Malvaceae), that produces one or more Bacillus thuringiensis Berliner (Bt) proteins is reduced by plantings of non‐Bt refuge cotton that produce non‐selected individuals. However, the contributions of non‐Bt, non‐cotton crop hosts to the overall effective refuge for H. zea on Bt cotton have not been estimated. A 2‐year, season‐long study was conducted in five US cotton‐producing states to assess the spatial and temporal population dynamics and host use of H. zea. Helicoverpa zea larval estimates in commercial crop fields demonstrated that non‐cotton crop hosts, such as maize, Zea mays L. (Poaceae), grain sorghum, Sorghum bicolor (L.) Moench (Poaceae), peanut, Arachis hypogaea L. (Fabaceae), and soybean, Glycine max (L.) Merrill (Fabaceae), collectively support much larger larval populations than cotton throughout the season. Larval populations were almost entirely restricted to maize in the middle part of the season (June and portions of July), and were observed in non‐cotton crop hosts more frequently and typically in larger numbers than in cotton during the period when production would be expected in cotton (July and August). Numbers of H. zea larvae produced in replicated strip trials containing various crop hosts paralleled production estimates from commercial fields. In contrast, the number of H. zea adults captured in pheromone traps at interfaces of fields of Bt cotton and various crop hosts rarely varied among interfaces, except in instances where maize was highly attractive. With the exception of this early season influence of maize, moth numbers were not related to local larval production. These data demonstrate that H. zea adults move extensively from their natal host origins. Therefore, non‐cotton crop hosts, and even relatively distant hosts, contribute significantly to effective refuge for H. zea on Bt cotton. The results presented here demonstrate that substantial natural refuge is present for Bt‐resistance management of H. zea throughout the mid‐South and Southeast portions of the US cotton belt.     

Consumptive and non‐consumptive effects of wolf spiders on cotton bollworms

Larvae of the cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) that survive on genetically modified Bt cotton (Gossypium hirsutum L., Malvaceae) contribute to the risk of widespread resistance to Bt toxins. Current resistance management techniques include pupae busting, which involves deep tilling of the soil to kill overwintering pupae. Unfortunately, pupae busting runs counter to soil and water conserving techniques, such as minimum tillage. This problem could be relieved with biological control methods, whereby predators attack either larvae going to ground to pupate or moths emerging from the ground. We found that the wolf spider Tasmanicosa leuckartii (Thorell) (Araneae: Lycosidae), a common inhabitant of Australian cotton agroecosystems, is an effective predator of H. armigera, attacking and killing most larvae (66%) and emerging moths (77%) in simple laboratory arenas. Tasmanicosa leuckartii also reduced the number of emerging moths by 66% on average in more structurally complex glasshouse arenas. Males, females, and late‐instar juveniles of T. leuckartii were similarly effective. Tasmanicosa leuckartii also imposed non‐consumptive effects on H. armigera, as when a spider was present larvae in the laboratory areas spent less time on the cotton boll and more time on the soil and more mass was lost from the cotton boll. Increased loss of boll mass likely reflects changes in H. armigera foraging behavior induced by the presence of spiders (indirect non‐consumptive effects). Helicoverpa armigera spent more time as pupae when the spider was present in simple laboratory arenas, but not in more complex glasshouse enclosures. Overall, results indicate that T. leuckartii spiders can be effective predators of H. armigera late instars and moths but also suggest that, under some conditions, the presence of spiders could increase the damage to individual cotton bolls.     

Impact of transgenic Bacillus thuringiensis cotton on a non-target pest Tetranychus spp. in northern China

Field studies were carried out to evaluate the effect of two transgenic cotton varieties (SGK321 carrying Cry1A+CpTI and DP99B carrying Cry1Ac) and the conventional variety (shiyuan321‐parental line of SGK321) on spider mites, Tetranychus spp. from 2002 to 2004. In 2002, this experiment included three treatments: Bt cotton field (SGK321) treated with acaricides against spider mites, untreated non‐Bt cotton field (Shiyuan321), and untreated Bt cotton field (SGK321). In 2003–2004, there are four types of treatments after a new transgenic Bt cotton variety, DP99B (non‐chemical control), was added into the experiments. The results showed that there were no significant difference in densities of spider mites among Bt without acaricides and non‐Bt without acaricides cotton fields, nor was there a significant difference in damage of spider mites to cotton among these treatments (P > 0.1). However, there are significant differences (P < 0.05) in densities of spider mites and damage caused by spider mites between cotton fields with and without acaricides. Acaricide significantly reduced the densities of spider mites in Bt cotton (P < 0.05). These results suggest that Bt cotton has no effect on spider mites populations. However, spider mites have the potential for severe damage in Bt cotton fields. Acaricides are essential tools in controlling cotton spider mites in northern China.