Lewis J. Wilson

A Comparison of Arthropod Communities in Transgenic Bt and Conventional Cotton in Australia

Abstract Transgenic Bacillus thuringiensis (Bt) cotton has had a major impact on the Australian cotton industry by largely controlling lepidopteran pests. However, it also may have other impacts on the invertebrate community that need to be identified. We compared the canopy invertebrate community in sprayed conventional, unsprayed conventional, and unsprayed Bt cotton over three seasons using suction sampling methods. We found that the diversity or species richness of the beneficial communities was reduced in the sprayed crops at two sites. Although spraying had the strongest effect on the community, there was a slight difference between the total community in unsprayed conventional and Bt crops, with crop type accounting for 4.5% of the variance between these communities. Out of over 100 species groups examined, the most consistent differences between unsprayed Bt and conventional communities were higher numbers of Helicoverpa in conventional crops (as would be expected) and slightly higher numbers of Chloropidae and Drosopillidae (Diptera), damsel bugs (Hemiptera, Nabidae), and jassids (Hemiptera, Cicadellidae) in conventional crops. With the advent of Bollgard II and the possibility that 80% of the cotton crop in Australia could be transgenic, the effects of these small differences in the transgenic and conventional communities should be monitored over the long-term to assess if any modifications to cotton management practices need to be made.

'Phytophagous' thrips are facultative predators of twospotted spider mites (Acari: Tetranychidae) on cotton in Australia

Predatory feeding on Tetranychus urticae Koch (Acari: Tetranychidae) populations on cotton by phytophagous thrips, Thrips imaginis Bagnall, T. tabaci Lindeman and Frankliniella schultzei Trybom (Thysanoptera: Thripidae), was investigated in the field and laboratory. Phytophagous thrips are a common early season pest of cotton in Australia, though their true pest status is undefined. In California, the phytophagous thrips (Frankliniella occidentalis (Pergande)) is regarded as an opportunistic predator of mite eggs, their consumption of which increases fitness over a diet of leaf tissue alone. Thrips are among the most abundant of insects on young cotton. If they consume mite eggs, even at relatively low rates, they could have a significant influence on the probability of survival of early season spider mites. Consumption of eggs of T. urticae by thrips was investigated in the laboratory. Second instar F. schultzei consumed more eggs per day (ca. 4 eggs per day) than did second instar T. tabaci or T. imaginis (ca. 1 egg per day). Consumption by first instar F. schultzei was much lower than for second instars. Adult T. tabaci consumed ca. 1 egg per day whilst adults of F. schultzei consumed only ca. 0.5 eggs per day, although some individuals of this species did consume substantial numbers of eggs. Larvae of all thrips species showed a type II functional response to prey density. In the field, adults and larvae of T. tabaci and F. schultzei showed a preference for cotton seedlings that were also infested by spider mites. In a glasshouse, larvae of T. tabaci showed a highly significant preference for feeding within mite colonies. In the field, suppression of predators, predominantly T. tabaci and F. schultzei, with a broad spectrum insecticide (dimethoate) contributed to outbreaks of mites occurring earlier than they would have otherwise. The results show that phytophagous thrips eat mite eggs and that they are potentially important predators of spider mites in the field, especially given their abundance on young cotton and preference for inhabiting situations in which mite colonies are found.

Organophosphate resistance in spider mites (Acari: Tetranychidae) from cotton in Australia

Tetranychus urticae Koch was resistant to all organophosphates (OPs) tested. The demeton-S-methyl resistance was extremely high (maximum resistance factor (RF) 650 X), as was the dimethoate resistance (maximum RF 750x). The parathion resistance was high (maximum RF 78X), while the profenofos resistance in T. urticae remained stable from 1976 until 1988 (approximately 15X) and that of monocrotophos from 1976 until 1989 (approximately 40X) after which the resistance rose. The resistance in T. urticae peaked in the 1995 season at levels of >100X for profenofos and >400X for monocrotophos, rendering both chemicals ineffective. Tetranychus ludeni Zacher was also resistant to all the OP chemicals tested, but at lower levels than for T. urticae. The LC 50 values indicated that the demeton-S-methyl and monocrotophos resistance in T. ludeni was an order of magnitude less than for T. urticae. The maximum profenofos resistance levels against T. ludeni (6.5 X ) were approximately one-quarter those of the maximum profenofos resistance levels against T. urticae (30X), The parathion LC 50 values and dimethoate RFs indicate T. ludeni to be ultimately only half as resistant as T. urticae. We consider that the relative lack of tolerance to OPs exhibited by T. ludeni may have contributed to it apparent disappearance from Australian cotton. Tetranychus urticae was the dominant mite pest in Australian cotton during 1976-1995. Tetranuchus ludeni reached damaging levels in the late 1970s but virtually disappeared from cotton during the 1980s.

The Present and Future Role of Insect-Resistant Genetically Modified Cotton in IPM

Transgenic cottons producing Cry toxins from Bacillus thuringiensis (Bt) provide for control of lepidopteran pests and were first commercially grown in Australia, Mexico and the USA in 1996. As of 2007, a total of six additional countries (Argentina, Brazil, China, Colombia, India, and South Africa) now grow Bt cotton on a total production area of 14 million hectares. The technology primarily provides highly selective and effective control of bollworms, which are the most damaging pests of cotton worldwide. It is estimated that between 1996 and 2005 the deployment of Bt cotton has reduced the volume of insecticide active ingredient used for pest control in cotton by 94.5 million kilograms and increased farm income through reduced costs and improved yields by US

Effect of early season insecticide use on predators and outbreaks of spider mites (Acari: Tetranychidae) in cotton

7.5 billion, with most of the benefit accrued by farmers in developing nations. Reductions in insecticide use have broadened opportunities for biological control of all cotton pests but most other pest management tactics have remained largely unchanged by the use of Bt cotton. However, several non-target pests have become more problematic in Bt cotton fields in some countries largely due to reductions in insecticide use for target pests. After 11 years of Bt cotton cultivation, control failures due to resistance have not been detected under field conditions. This success can be largely credited to pre-emptive resistance management based on mandated refuges and monitoring programs as well as non-mandated refuge crops and natural refuges which collectively act to dilute any resistant alleles in pest populations. New products are in the pipeline to improve the effectiveness of genetically modified cotton cultivars for resistance to lepidopteran pests, and to address other pest problems in cotton. Debate over food and environmental safety, regulatory oversight, and farming community welfare are likely to continue as the technology moves forward with new crops and new adopting countries.

Target and non-target effects on the invertebrate community of Vip cotton, a new insecticidal transgenic

The Australian cotton industry relies almost exclusively on synthetic insecticides for control of early season pests. These insecticides often disrupt predatory insect activity in the field. Potential predators of the twospotted spider mite, Tetranychus urticae Koch, in cotton, identified in field and confirmed in laboratory experiments, included a theridiid spider, a phytoseiid mite, a lacewing larva, predatory thrips, several Coccinellidae and several Hemiptera. These predators were mostly generalists, having previously been reported as predators of aphids or caterpillars of Helicoverpa spp. The effect of insecticides on T. urticae and its predators was evaluated in three field experiments. Cotton was artificially infested with T. urticae then sprayed five times at seven to ten day intervals with either dimethoate (140 g ai/ha), thiodicarb (750 g ai/ha and 187.5 g ai/ha), endosulfan (735 g ai/ha and 367.5 g ai/ha), methomyl (169 g ai/ha) or amitraz (400 g ai/ha). Tetranychus urticae populations reached higher densities in dimethoate, thiodicarb and methomyl treated cotton than in untreated cotton. Population densities of T. urticae in cotton treated with low rates of endosulfan or thiodicarb were similar to controls, while those in cotton treated with amitraz were lower. All insecticides caused significant reductions in at least one predator group. Significant negative relationships were found between early season abundance of predators and the mid-season abundance of T. urticae and positive relationships between predators and the lag-period for T. urticae outbreaks to develop. Predation is implicated as a key factor influencing the early season survival of T. urticae . The implications for developing integrated pest management strategies in cotton are discussed.

Implementing Integrated Pest Management in Australian Cotton

A new transgenic cotton producing the Vegetative Insecticidal Protein (Vip) is being developed to control Lepidopteran pests, especially Helicoverpa larvae. Before its introduction its efficacy against Helicoverpa larvae under field conditions needs to be confirmed, and any non-target effects it may have on the arthropod community need to be identified. We conducted field trials to compare the arthropod community in unsprayed conventional (Sicala 40) and Vip (Coker 312 Vip3A, event 102) cotton using visual searches, beatsheets, and suction samplers at 2 sites in Australia. At both sites, Vip controlled Helicoverpa larvae leading to much higher boll counts. There were no major differences in either species richness or diversity of the beneficial and non-target communities between Vip and conventional cotton, although cotton cultivar accounted for 2–7% of the variance in arthropod communities. There was no detrimental effect of Vip cotton on egg parasitoids. The number of predatory beetles and the pest mirid Creotiades dilutus (Stal) was higher in the Vip, although the increase in mirids was probably the result of more food (bolls) in the Vip crop. In a small plot experiment, we found higher numbers of whitefly in Vip, but this may be driven by differences in leaf hair between the cotton cultivars. Vip cotton appeared to have little effect on the arthropod community other than on Helicoverpa. As such it has the potential to be a useful tool in the management of Helicoverpa and may relieve resistance pressure on existing Bt cultivars (transgenic cotton containing genes for insecticidal Cry proteins), thereby increasing the durability of both technologies.

Seasonal abundance and distribution of Tetranychus urticae (Acari: Tetranychidae), the two spotted spider mite, on cotton in Australia and implications for management

The Australian cotton industry faces a number of challenges in pest management. These include damage due to a number of key pests [Helicoverpa armigera and H. punctigera, spider mites (Tetranychus urticae), aphids (Aphis gossypii) and mirids (Creontiades dilutus)],insecticide resistance in the primary pest (H. armigera) and two secondary pests (mites and aphids), escalating costs of production and environmental concerns over off-farm movement of insecticides. To address these issues, a major research effort has focused on reducing dependence on insecticides through the development and implementation of integrated pest management (IPM) systems. As with IPM systems in other cotton-producing countries and in other crops, the Australian cotton IPM system emphasises the use of a range of tools to manage pest populations, with insecticides seen as a last resort. What is unique about the approach taken in Australia is a higher emphasis placed on the role of beneficial insects in IPM, the heavy involvement of cotton growers and consultants in the development of the system, the emphasis on incorporating IPM as a component of the overall farming system, and the role of IPM groups, where neighbouring growers agree on a common set of IPM goals, communicate regularly and support one another to achieve group goals. This participatory action research approach provides a framework for ensuring the cotton industry is fully engaged with the research effort (Dent 1995), claims ownership of the research, and becomes a driver of the IPM program (Ooi 2003).

Advances with Integrated Pest Management as a Component of Sustainable Agriculture: The Case of the Australian Cotton Industry

The two spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), is a pest of cotton in Australia yet has received little attention. To develop sampling strategies for pest management the seasonal abundance and intra-crop distribution of T. urticae on cotton was studied. T. urticae colonized cotton crops at seedling emergence in October. Populations declined through November/December then increased progressively thereafter, at varying times and rates. Higher initial infestation levels were correlated with earlier, potentially more damaging, mite outbreaks. Survival of T. urticae through November/December appears crucial in determining the extent to which this potential is realized. Nodes 3 to 5 below the terminal were most heavily infested and should be used as the sampling unit for mites. The within plant distribution of T. urticae was unaffected by cotton variety or insecticide applications. T. urticae was more abundant on the edges of fields than in the interior early in the season (October and November) indicating colonization from an external source. The edge effect diminished with time, suggesting a lack of continuous colonization. The only exceptions to this pattern occurred when T. urticae migrated from senescent maize crops into the nearby cotton crops in early January. A simple sampling technique, based on the presence or absence of mites on leaves was developed for pest management purposes.

IPM in the transgenic era: a review of the challenges from emerging pests in Australian cotton systems

Insect pests represent a significant limitation for production of many crops. Traditional reliance on pesticides brings significant economic costs and environmental liabilities of off-target drift, chemical residues and resistance. IPM has long been proposed as an alternative. The adoption of IPM in the Australian cotton industry provides a valuable overview of the key components of IPM and the issues around successful implementation. IPM must be founded on a thorough understanding of the ecology of pest and beneficial species and their interaction with the crop and will provide a range of tactics which must be integrated by the producer to achieve economic and environmental sustainability. The emerging era of insect resistant transgenic cottons offers real prospects to provide a foundation for more sustainable, economically acceptable IPM with the integration of a range of non-chemical tactics and much less reliance on pesticides.