The project initially aimed at assessing the potential of Eretmocerus mundus (APF) as a control agent for silverleaf whitefly (SLW). As the crops where SLW is a pest are annual, mechanisms of achieving early colonisation need to be assessed. Further, a broad range of pesticides are used in these crops and their potential impacts on the parasitoid are unknown. The capacity of E. mundus to control field infestations is also untested.

After the second year it was apparent that while E. mundus performed well under controlled conditions it lacked the ability to exert sufficient control on outbreaking populations. A decision was made to then to better understand the interaction between the native Bemisia tabaci and the exotic B biotype. The background to this shift was the observations that in the cotton growing areas of QLD SLW was patchily distributed and rarely found on cotton. In NSW, surveys of cotton in 1995 and 1996 found small numbers of SLW. Since then 100 leaves have been collected from more than 190 crops with no SLW being recovered. By way of contrast, in both NSW and QLD, the Eastern Australian Native (EAN) biotype of B. tabaci occurs commonly in cotton, although at densities of less than 3 individuals per leaf. The most common whitefly species in cotton remains the greenhouse whitefly (Trialeurodes vapororarium). The reasons for the low numbers of SLW was unclear but there were several possibilities. The most likely of these was an interaction between the two biotypes of Bemisia tabaci, climatic suitability and host availability.

Resistance is an ongoing concern with the management of H.armigera in the Australian

cotton industry. Management strategies are in place to either prevent, or retard, further

development of resistance to either chemical insecticides or to the Cry1Ac protein in

transgenic plants. However, these strategies, particularly those concerning the Cry proteins, are based on models of resistance, as information is lacking regarding putative resistance genes in H. armigera. This project aimed to increase our understanding of the genetic basis of resistance ideas, about which underlie the basis of the resistance management strategies.

The focus was on Bt resistance, but the work is also directly applicable to conventional

chemistry insecticide resistance.This project was a collaborative one between the CSIRO genetics group in Canberra and Dr Heckel's group at the University of Melbourne. It made use of recent advances in genetic studies of H. armigera, in particular, the development of a genetic linkage map by Dr Heckel

for this species, developed through the use of AFLPs. Linkage maps enable a speedier means to define the genetic basis of resistance than is available through more conventional approaches.

The role of a Trainee Industry Development Officer working with grower groups in the Border Rivers region, has given a good understanding of cotton industry issues and grower practices. The formal training in the Cotton Production course and the other extension courses has given me a good technical background in production and extension. By participating in various industry updates and conferences I was able to gain understanding of the current research and problems within the cotton industry. Maintaining a network of contacts within the cotton industry allows me to keep up to date on issues within the industry as well as a broad source of information to call upon.

Training in all aspects of cotton production with particular attention given to the following disciplines.

• Integrated pest management

• Plant physiology and nutrition

• Soil and irrigation management

• Establishing effective growers groups and networks.

Helicoverpa spp. are arguably Australia’s most important insect pests, costing the

economy $200-300M annually. Significant advances in the management of

helicoverpa have been made since the last workshop in 1995.

A two day workshop at Toowoomba on 21-22 June 2004 provided an opportunity for

around 50 participants with interest in helicoverpa R,D&E from State Agriculture

Departments, CSIRO, Universities, R&D Corporations, consultants and industry to

discuss issues related to the management of these pests in grains, cotton and

horticulture. The first day involved a series of short review presentations to set the

scene, followed by questions and discussion from the floor. The second day

involved workshopping sessions to tease out priority issues, identify gaps and

provide direction for future research.

The objectives of the workshop were to:

(a) review the developments in R,D&E related to helicoverpa management in

Australia since the last workshop;

(b) review the role of extension in the development and implementation of Area-

Wide Management (AWM) programs by growers in north-east Australia;

(c) examine the prospects for successful AWM, and

(d) provide direction for future R,D&E requirements for these pests.

Whilst the focus of the workshop R,D&E concerned with advancing knowledge and

management capacity of Helicoverpa spp., there was some discussion about the

benefits that could accrue to industries or regions, or in managing other pest

species, from extending techniques used successfully with helicoverpa.

Key factors in managing transgenic Bt cottons for the future are to have an effective resistance management strategy. An essential component of any such strategy is to establish a resistance monitoring program. The core components of this project address resistance monitoring as well as examine the performance of transgenic cotton (two genes) in relation to resistance management. To develop an effective resistance management strategy it is important to understand the mechanisms of resistance as well as the possible behaviour changes that may occur within a resistant population as compared to a susceptible one. If the industry is to continue to use Dipel® and other foliar Bts, then the question of cross resistance between Bt proteins also needs to be evaluated.

To undertake this type of research it is important to develop colonies resistant to both Bt proteins used in transgenic cotton (i.e. Cry 1Ac and Cry 2Ab) and foliar Bts (Dipel®). To establish resistant colonies, surviving larvae have been reared in the laboratory. A colony with low to moderate resistance to MVP® (Cry 1 Ac), and lower order cross-resistance to fully expressing Bt transgenic cotton plants has been established. Further selection of the strain with MVP® and Ingard® plants should result in fully resistant colonies.

To help understand the underlying basis of the resistance to pirimicarb, and hence improve the chance of effective management, Dr Robin Gunning and Dr Graham Moores (Rothamstead, UK) did a preliminary screen on resistant clones. They found that the underlying resistance biochemistry (resistance mechanism(s)) is probably a target-site insensitivity and furthermore suggested that pirimicarb resistance can be maintained without selection. Once selected resistance should therefore persist through the season and overwinter causing ongoing and progressively worsening control problems.

Cotton Aphid: Due to its ability to rapidly develop resistance cotton aphid (Aphis gossypii Glover) is world-wide the major aphid pest of cotton. It causes significant problems in Thailand, The Sudan, Russia and the USA. In Australian cotton it is a persistent secondary pest with potential to become a major pest due to resistance.

Resistance allows the uncontrolled increase in aphid numbers causing their sugary honeydew secretions to contaminate the cotton lint. This causes significant discounts due to the need to clean the cotton before it can be spun in today’s high speed spinning equipment. Such a scenario happened recently in the USA causing an immediate and substantial downgrading of the contaminated lint value. Recent Australian research has also confirmed that uncontrolled aphid outbreaks earlier in the cotton season can significantly impede plant development, through aphids competing for plant assimilate causing dramatic yield reductions (up to 75 %). As cotton production in Australia is a 1.5 billion-dollar industry uncontrolled resistance would be a national disaster, due to loss of yield but more significantly damage to our international reputation as a producer of ‘clean’ cotton.

Resistance management in Australia is further complicated because cotton aphid reproduces asexually with female aphids giving birth to live female ‘clones’. Unmanaged insecticide use can rapidly kill susceptible clones, leaving only resistant clones. Further use of the same insecticide group then may select for genotypes within the resistant clones that have small transcription errors or mutations that favour fitness or confer other mechanisms of resistance. Selection of resistant clones allows the rapid proliferation of resistance because there is no outcrossing with susceptible wild types. A second pest aphid, the green peach aphid is also a sporadic but at times damaging pest in cotton. This species is already widely resistant to a range of insecticides and can present major control problems for cotton growers.

Two-spotted mite: Worldwide over 33 species of mites attack cotton, but in Australia damage is due mainly to three species of Tetranychid mite, the banana spider mite (Tetranychus lambi), the bean spider mite (T. ludeni) and the two-spotted mite (T. urticae), though the latter is by far the most common. Two-spotted mite is extraordinarily adaptable and renowned for developing resistance to chemicals used for its control. Two-spotted mite is acknowledged as the most serious world mite pest of agriculture due to its ability to develop resistance and in Australia uncontrolled resistance has rendered some horticultural crops uneconomic. Two-spotted mite has been the dominant mite pest in cotton since the early 1980s. Uncontrolled populations can cause significant losses of yield and fibre quality.

Fusarium wilt, caused by Fusarium oxysporum f. sp. vasinfectum (Fov), is a destructive disease of cotton (Gossypium hirsutum L) in almost all cotton producing countries of the world. First reported in 1993, this disease is now widespread in Australia and is causing substantial losses. Previous studies identified two distinct genotypes in Australia (VCGs 01111 and 01112) that were morphologically distinct from the eight races of Fov found outside Australia, but prior to this study the origin(s) of the Fov in Australian cotton fields were unclear.

There are 17 native Gossypium species or wild cottons in Australia, some of which have ranges that overlap cotton-growing regions. Wild crop relatives are a traditional source of novel resistance genes for many plant diseases, and preliminary studies of Australian Gossypium species suggested they may contain some useful levels of Fusarium wilt resistance. At the same time, however, it was possible that the native species could be harbouring potential cotton pathogens. The main objectives of this project was to explore the risk and the potential of the Australian Gossypium species, specifically 1) to screen accessions of native Gossypium species for Fov resistance; 2) to determine if Fusarium wilt pathogens occur in native Gossypium populations; and 3) to investigate the genetic relationships between Fov causing the disease in Australian cotton fields and indigenous F. oxysporum associated with native Gossypium populations.

Screening the Australian Gossypium species identified a range of accessions that will be useful in the continuing efforts to new cotton cultivars with improved levels of Fusarium wilt resistance. Although there was considerable variation in Fusarium wilt resistance among the Australian Gossypium species, G. sturtianum emerged as a possible source of novel resistance genes. At the same time, a number of susceptible G. sturtianum accession were identified that can be used to generate segregating populations for genetic analyses. Future genetic analysis will assist cotton breeders by providing a clearer picture of how Fusarium resistance is controlled genetically.

Simultaneously, it has become clear that while the native Gossypium species are not harbouring cotton field pathogens, there are some of the native soil fungi of potential concern and continuing vigilance would be appropriate.

Fusarium wilt is an endovascular disease, and while endovascular fungi are commonly found in the stems of the wild Gossypium species, with only one exception, none of the 600+ isolates tested were related to cotton field pathogens. More importantly, pathogenicity trials of these endovascular fungi established that none of these isolates have the ability to invade cotton through the roots and cause wilt symptoms, and therefore are highly likely to give rise to new cotton field pathogens. It is unlikely that the native Australian Gossypium species are harbouring potential new pathogens that will impinge upon the Australian cotton industry in the future.

Surveys of soils from the native cotton populations and native vegetation in the Norwin—Boggabilla region, where Fusarium wilt was first detected, identified a range of diverse Fusarium oxysporum genotypes. Broadly speaking, these genotypes fall into one of five distinct lineages, designated A to E. Pathogenicity trials established that 14% of these Fusarium oxysporum genotypes could induce mild Fusarium wilt symptoms on cotton. While none of these isolates currently are virulent enough to cause plant death, isolates in lineage A have emerged as the closest known relatives of the cotton field pathogens, and it is now certain that the origin of the cotton field pathogens can be traced to native Fusarium oxysporum genotypes. Whether other Australian genotypes have the same potential to develop into new cotton field pathogens will be the focus of ongoing research.

The silverleaf whitefly is characterised by a huge host range, high fecundity, the ability to induce physiological responses in plants, transmit plant viruses, the copious production of honeydew, and an extreme ability to develop insecticide resistance. The whitefly damages cotton crops by direct feeding (yield can be reduced by 60% under heavy infestation), copious production of honeydew (which contaminates cotton lint and reduces the photosynthetic efficiency of cotton leaves) and by virus transmission.

B-biotype B. tabaci came into Australia with insecticide resistance to most pyrethroids, organophosphates and carbamates. Explosion of the silverleaf whitefly into horticultural crops in north Queensland during the late 1990’s ensured development resistance to other insecticides (bifenthrin, endosulfan, amitraz and imidacloprid) to which they initially susceptible. Field selection experiments in horticultural crops in North Queensland (DAN 106C) showed a very rapid rate in the selection of resistance to insecticides.

At the commencement of this project, B-biotype B. tabaci was not a pest of cotton but was considered to be a major threat to the Australian cotton industry needing pre-emptive research. The aims of this project were therefore, to monitor silverleaf whitefly numbers on cotton, secondly to monitor insecticide resistance levels and to investigate novel insecticides and insecticides combinations as candidates for whitefly control. In December 2001, the silverleaf whitefly exploded on cotton in central Queensland and reached economically damaging levels.

The major challenge to sustainable use of Bt cotton is the risk that the target pests, Helicoverpa spp, may evolve resistance to the engineered toxins. Resistance to conventional Bt sprays has evolved in field populations of other moths (e.g. Plutella xylostella), H. armigera has consistently developed resistance to synthetic pesticides in the field, and cultures of Bt resistant strains of H. armigera have been generated in the lab. Bt resistance concerns are thus well-founded. Much effort has therefore been devoted to developing and implementing pre-emptive resistance management strategies, most notably based on the use of refuges to maintain sources of susceptible moths in the population which will mate with potentially resistant individuals produced in Bt crops - thus dampening the development of resistance. This project aimed to help identify the most productive refuge options. Such information is essential to allow robust estimates of refuge sizes. Crops considered in CSE90C included sprayed (non Bt) conventional cotton, unsprayed conventional cotton, pigeon pea, sorghum, maize and soy bean.

One of the major criteria defining effective refuges is that they will generate enough susceptible moths to ensure that matings between resistant survivors from Bt crops are extremely unlikely. But our knowledge underpinning the optimal placement of refuges within a landscape and how well the moths generated there disperse to Bt crops is very limited. Some studies have simulated movements of H. armigera from refuges to transgenic crops using the model HEAPS and argued that dispersal from refuges can be patchy according to wind speed and direction and spatial distribution of crops. The qualities of plant hosts at source and sink, aggregative / synchronous movement behaviours of the moths and limits of simple diffusion are also considered likely to be important. But empirical data from the field on all this are scarce. In CSE90C, we sought to use strontium to mark moths in refuges and set traps to recapture them in nearby Ingard cotton crops.

Many questions about the seasonal abundance and resistance dynamics of Helicoverpa require knowledge of which crops contribute to local populations. While we can infer something about the relative importance of different crops from pupal numbers, the definitive answers require that we can assign moths to probable crop origin. We intended to do this, and thus infer local movements of moths, using the ratios of carbon isotopes that vary between C3 (cotton, legumes) and C4 (maize, sorghum) plants and thus are likely to be transferred to moths reared on them.

Despite some previous research on cultivation and its usefulness in reducing the abundance of over-wintering pupae of Helicoverpa (“pupae busting”), questions often arise as to the best tillage methods to use to achieve this. We intended in CSE90C to establish field trials, in collaboration with soil scientists, to determine optimum methods amongst commonly available machinery to destroy pupae, whilst taking into consideration the impact of such methods on soil structure and fertility.

The project focussed on understanding more about the egg parasitoid Trichogramma pretiosum. This minute wasp attacks the egg stage of heliothis (Helicoverpa spp.) and causes significant mortality of heliothis on the Darling Downs.

T. pretiosum is a new species to the Darling Downs. It is native to North America, but was established in the Ord River region of Western Australia in the mid 1970’s. The DPI obtained some T. pretiosum from scientists in Western Australia and released it onto the Darling Downs in 1995. It appears to thrive in agricultural environments, especially when selective pest management tactics are employed, e.g. Bt. cottons and the use of selective insecticides.

There is increasing grower interest in utilising beneficial insects and spiders in pest management, and thereby reducing the need to spray pests with insecticides. Cotton growers on the Darling Downs are interested in learning more about Trichogramma because of the high impact the wasps have had in dryland cotton. In particularly, leading consultants and growers want to know if T. pretiosum can be utilised in irrigated cotton and conventional cotton.

The project built on the findings of previous research where T. pretiosum successfully managed heliothis in unsprayed dryland INGARD® cotton for three consecutive years, including a high pest pressure year when heliothis egg densities rose to 90 eggs/m. Previous DPI research found that T. pretiosum is a significant natural enemy of heliothis (DAQ 96C –“IPM in dryland cotton on the Darling Downs’). This work was carried out in dryland INGARD® cotton at Jimbour on the Darling Downs. The research reported here was conducted in other regions, and included trials in irrigated conventional cotton.