Verticillium wilt of cotton is caused by Verticillium dahliae, a soil borne fungus that enters the roots and grows into the vascular system of the plant. Identifying Verticillium is the first step in being able to manage it.

This two-year trial aimed to explore soft management options for whitefly management in the southern valleys. The drivers of this were, managing the risks associated with sticky cotton and the wider industry impacts that were occurring to neighbouring industries such as horticulture. The first year of the trial focused on the use of oils and detergents as a means of control in a small plot, replicated trial at the Irrigation Research Extension Committee Farm, coupled with sticky trap monitoring and a small area of parastoid wasps, Eretmocerus hayati, released. The results from the first year found that there was no benefit from the use of sticky traps in terms of trying to detect a whitefly population earlier. There was also no significant difference between the detergent and oil treatments.

Second year trial looking at the best soft management options after consultation with the wider growing community in the Whitton region, the project direction was changed to broadscale management of whitefly through a combination of soft pesticide applications, oils and the release of Eretmocerus hayati across a wide area to try and influence populations. Sticky traps where used again to try and detect populations earlier. Once again, the sticky traps proved to be of no benefit in the early detection of whitefly. Higher levels of parasitism were achieved where releases were made as expected but from the data collected it was possible to see that the release of the whitefly parasitoids resulted in higher levels of parasite nymphs and a lower whitefly population by the end of the period. It was also possible to see that other fields on the farm where parasites were released, but not directly released on had spikes in the parasitism levels as well as reduced overall whitefly nymph numbers, consistent with the fields that had the releases. The data collected, shows that there was some success in the use of parasitiods for helping reduce the numbers of viable nymphs. Some of the challenges that we will continue to face going forward, are the need to commit to using the wasps at the start of the season when there is no way of knowing what the end of season pressure will be like, and the issues around getting the wasps due to northern demand. There was also an issue with some growers opting to spray fields early rather than allow the parasitised field run their course so we had to remove some data. Overall, the practice change of heading towards the use of beneficials from this work appears viable and this provides some confidence to the growers that they can offer some level of control.

This travel funding sponsored attendance at the intital planning meeting for the Rural R&D for Profit project “Improving Plant Pest Management through Cross Industry Deployment of Smart Sensor, Diagnostics and Forecasting”.

The introduction of insecticidal transgenic varieties into the Australian cotton market in the mid-1990’s allowed the industry to substantially reduce its pesticide use but resistance continues to threaten its efficacy. Indeed, CSIRO has isolated resistance in the key targets H. armigera and H. punctigera to all three toxins (Cry1Ac, Cry2Ab, Vip3A) in the current Bollgard 3 varieties. This is set in the context of an emerging global pesticide crisis that could see novel resistant variants of these pests selected elsewhere arrive into Australia.

The industry relies on a pre-emptive strategy to slow the development of Bt resistance. This is underpinned by independent monitoring of background resistance frequencies to enable the industry to autonomously respond to emerging issues, as well as research on other high priority stewardship issues related to Bt resistance in Helicoverpa species. The project was conducted in the following three parts.

PART 1: Does multiple resistance to Bt toxins in Helicoverpa spp. pose a threat to 3 gene cotton?

There is a high chance of an insect being resistant to Cry2Ab and Vip3A. Cry1Ac declines as plants age which creates selection opportunities. Our laboratory bioassays demonstrated that it is possible to select for Cry1Ac resistance in a Cry2Ab / Vip3A background.

Experiments with multi-resistant colonies (created from resistant field colonies) challenged with field grown 3-toxin cotton suggest that they carry a fitness cost but can nevertheless survive well from the neonate to 3rd instar stage. As the larvae mature they are likely to die on 3-toxin cotton but a small proportion can survive.

PART 2: Are the frequencies of resistance to 3 gene cotton increasing?

During 2017/18, we used F1 screens to sample populations of H. armigera and H. punctigera throughout the industry and did not find evidence of increases over time in the frequencies of resistance to Cry1Ac, Cry2Ab and Vip3A. We also performed F2 screens and did not isolate any dominant forms of Bt resistance but we did isolate a new recessive Vip3A resistance in H. armigera. Our continued survey of CCA members since 2008 supports frequency estimates which suggest that Bt resistance in Helicoverpa species is not increasing.

To assist with development of the molecular tool (as part of CSE1801) we examined F2 and F1 individuals previously identified as resistant using bioassays during our monitoring program. We: (1) screened for previously identified mutations and (2) examined whole genome data for novel mutations.

PART 3: What are the characteristics of different variants of Cry2Ab resistance?

There is no indication from our characterisation work that a novel variant of Cry2Ab resistant H. armigera poses a different threat to that of the first isolated variant.

Summary: It is unclear to what degree multiple resistance to Bt toxins in Helicoverpa spp. is a threat to stacked gene cotton. Our data suggest that currently there is no reason to consider changes to the Resistance Management Plan for Bollgard 3 cotton. However, it will be important to get a more complete understanding of the characteristics of the various isolated Vip3A resistance colonies to inform future methods / tools for monitoring resistance. It is also essential to validate the molecular tools being developed with standard bioassays to translate and incorporate them into future monitoring programs. Although there currently is no evidence of increasing resistance, it is critical to pre-emptively ascertain any future changes due to, for example, incursions of novel resistances from overseas and/or changing climates driving local selection in Helicoverpa and/or other pests that may carry novel resistance genes to key technologies used in Australia (i.e., Fall Armyworm).

Helicoverpa punctigera, along with Helicoverpa armigera, are major pests in Australian cotton. They are currently controlled using “Bt cotton” which contain genes derived from the bacteria Bacillus thuringiensis, that produce proteins toxic to Helicoverpa. While most effort has focused on preventing Helicoverpa spp. developing genetic resistance to these toxins, laboratory studies have shown that larvae which are not resistant are able to tolerate low to medium levels of toxin. This “induced tolerance” could lead to larvae surviving on Bt cotton without being resistant, and it could provide a stepping stone to the development of resistance. While Helicoverpa are known to develop some tolerance after one generation of exposure to Bt toxins, we did not know whether exposure is required throughout the entire larval period or only during particular instars. The aim of this summer project was to test if exposing the larvae Helicoverpa punctigera at different larval stages to 2% or 5% toxin concentrations of the discriminating dose of Cry1Ac toxin (used by CSIRO’s Resistance Team) would affect larval development and lead to tolerance in their offspring.

The results confirmed that after exposing only one generation of larvae to low levels of Cry1Ac toxins their offspring were able to tolerate higher levels of Cry1Ac than the controls. In addition we found that larvae exposed to Cry1Ac in early instars overcompensated their growth once they fed on non-toxin diet, and those exposed as late instars actively tried to avoid the toxin and developed into smaller moths. While the offspring of larvae exposed to 5% toxin as late instars showed the most tolerance, those exposed to 2% toxin as late instars also produced significantly more tolerant offspring. These results indicate that the critical period for the development of tolerance is late in larval development.

These results have implications in respect to Bt cotton efficacy, and could have implications in respect to the placement of refuges. They suggest that larvae moving off other crops and completing their development in Bt cotton could produce offspring at least as tolerant as those completing their development within the Bt crop. Therefore ideally refuges need to be far enough away from Bt cotton to avoid older larvae moving into the cotton.

Green mirids, Creontiades dilutus (Hemiptera, Miridae), are polyphagous bugs and are endemic to Australia. These bugs feed on a variety of plant species that grow across massive expanses of subcoastal agricultural landscapes in eastern Australia, as well as in the arid continental interior. Molecular evidence, along with field surveys, have demonstrated that C. dilutus bugs move long distances between native vegetation in the arid interior and crops in the eastern states of Queensland and New South Wales. These bugs arrive in the subcoastal agricultural landscapes every summer, and are important pests of cotton (Gossypium hirsutum L.) (Malvaceae). They feed on the soft tissues of cotton plants, including the developing flowers, which results in a substantial loss of fruit (cotton bolls) and the feeding damage delays harvest through the crops taking time to compensate for these losses.

The seasonal invasions of bugs into cotton are influenced by the high mobility of these insects and their ability to use a wide variety of host plant species across arid and agricultural landscapes. Some plant species are relatively good hosts in supporting the production of high numbers of nymphs, whereas others produce few nymphs but may be used incidentally as shelter, and this may aid in the dispersal of the adults across long distances. The timing of invasions of C. dilutus bugs into cotton, and the pathways followed by them are poorly understood. Also, the general mechanisms by which these insects localize appropriate host plants have not been subject to much investigation.

Host plant availability in the arid continental interior is dependent on highly variable localized rainfall, and such areas are separated by large expanses of extremely dry regions containing few green plants. In agricultural systems, non-crop plants along roadsides and the margins of farms occasionally host low densities of bugs, but previous field surveys have not found high densities of C. dilutus that may act as a source of pests that invade cotton. Within farms several legume crops, such as lucerne (Medicago sativa) and pigeon pea (Cajanus cajan) (Malvaceae), routinely support high bug densities, whereas nearby cotton crops host substantially fewer bugs. Gut analyses conducted previously suggest that individual mirids do

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move from lucerne into cotton, but they also move in the other direction, despite the differential numbers of bugs across these crops. Similar movement patterns across pigeon pea and cotton “boundaries” were evaluated in this thesis.

The ambiguity in the dispersal and host use patterns of C. dilutus bugs makes it difficult for pest managers to predict invasions of these insects into cotton, with accuracy. Consequently, researchers are not able to design effective management strategies. With a better understanding of dispersal and host use patterns of C. dilutus bugs, it may be possible to reduce the number of insecticide sprays in cotton if bugs could be attracted away from cotton by planting alternative hosts (trap crops), but these alternative hosts may inadvertently become local reservoirs of pests that move into cotton. A particular aim of this study is, therefore, to investigate aspects of the dispersal of these C. dilutus bugs across crop host species and the associated host localization behaviour of these insects. The ultimate goal is to use this information to form a conceptual model for the host localization process of C. dilutus bugs and provide a realistic framework to develop effective pest management decisions in cotton systems.

Specifically this thesis presents the results of: 1) surveys that asked pest managers about their perceptions of invasion patterns, 2) field surveys across vast arid and agricultural landscapes to identify which host species are used most consistently by bugs, 3) molecular evaluations to confirm feeding and movement of individuals across different hosts, and 4) behavioural experiments to identify host-associated cues used by bugs to localize specific plants.

Findings from this study indicate that most pest managers reported that the earliest seasonal infestations into cotton are associated with the proximity of cotton to legume crops and also with storms that move in from the arid regions to the west. Infestation patterns are consistent with multiple invasion events in each season and into each crop, and a gradual increase in bug numbers as nymphs develop into adults within squaring (flowering) cotton. Field surveys

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in the arid zone found that the highest densities of bugs were found on Cullen australasicum (Fabaceae) and Goodenia cycloptera (Goodeniaceae), at a time prior to when cotton was planted, and on lucerne and pigeon pea in agricultural systems during the flowering period of cotton.

Similarly, too, bug densities were consistently much higher on pigeon pea than on cotton. Creontiades dilutus bugs were found in the field to feed on both pigeon pea and cotton, and frequently they move back-and-forth between these crops, as found across lucerne-cotton boundaries. Behavioural tests in the laboratory revealed that these bugs are arrested in the vicinity of pigeon pea and cotton by olfactory cues, but there was no evidence that olfactory cues alone attracted bugs to either host beyond a range of 2cm. Also, this is the first behavioural study that observed an increase of insect locomotion at night, suggesting that these bugs are essentially nocturnal.

Collectively, the results of this thesis indicate that C. dilutus bugs are produced in relatively greater numbers on specific plant species than on nearby alternative species (with cotton being a relatively poor host ecologically (although not economically)). Olfactory cues that arrest bug movement to a locality appear to have a stronger influence on settling patterns across host plant species than do olfactory cues that attract bugs towards plants. A general host localization model is proposed in which high densities of bugs develop on host plant species that maintain soft tissues (after receiving rain or growing on irrigated farmlands), then move across the landscape and land on plants until recognizing cues that arrest their movement. Other host species, such as cotton, are used if their primary hosts are not available. The implications of how these bugs persist in highly variable environments are discussed, and the implications for pest management are specified.

CRDC's Strategic RD&E Plan is CRDC’s primary RD&E planning document and provides a high-level overview of CRDC’s strategic direction for the next five years. CRDC's vision is to power the success of Australian cotton through world-leading RD&E, and the Plan sets out how this will be achieved: the goals, investment approach, and planned impact. The Plan is ambitious: over the course of the five years, CRDC aims to contribute to creating $2 billion in additional gross value of cotton production through investments in RD&E. These investment will be split across the five key focus areas of the Plan: increasing productivity and profitability on Australian cotton farms; improving cotton farming sustainability and value chain competitiveness; building the adaptive capacity of the Australian cotton industry; strengthening partnerships and adoption; and driving RD&E impact.

CRDC 2013-2018 Strategic R&D Plan under its Responsible Landscape Management theme, outlines the industries desire to lead in managing natural resources and be recognized for its leadership in environmental performance. This project built on the past decade of investment in NRM research by providing a National NRM technical specialist who helped the industry meet this strategic goal through:

• developing and implementing annual national NRM campaigns,

• continuously improving the industries best practice recommendations for

NRM, and

• facilitating the capture of past and current NRM research into project

activities, outputs and outcomes.

A key measure of success under this goal as outlined within the Strategic plan is 1000km of riparian land and one million hectares of floodplain vegetation managed under best practice.

Uptake of phosphorus (P) by cotton crops demonstrated an excellent correlation with lint yield. Despite high levels of P fertiliser being applied, crops in Kununurra took up less than 15 kg P/ha and failed to produce lint yields greater than 8 bales/ha. Lint yields and P uptake at Narrabri however were considerably greater, indicating that another factor was preventing P uptake at Kununurra and thus limiting yield potential. These results confirm the P fertiliser recommendations suggested in the NUTRIpak manual.