This project examined how and when individual Helicoverpa armigera carrying a resistant allele (BX) were favoured in field-grown cotton, particularly on Ingard®. BX-like and other forms of resistance to Cry1Ac were found to be rare in field populations of H. armigera. It follows that individuals that carry will almost exclusively be heterozygous. We measured the survival and growth of heterozygous larvae and homozygous susceptible larvae on leaf samples from field-grown Ingard® and conventional varieties of cotton. By performing assays throughout the season, we were able to identify occasions that favoured heterozygotes and thus the evolution of resistance. Averaging relative survival rates of heterozygotes and homozygous susceptible genotypes over the 2002 - 03 and 2003 - 04 seasons we found that, over the first season, susceptible individuals would have survived and grown only half as frequently as the heterozygote. In the second season susceptible individuals fared slightly better surviving 0.68 as well as the heterozygote. Computer models were prepared that incorporated this information as well as new information on the frequency of Cry1Ac resistance in the field.

A second aim of the project was to detect and isolate alleles that conferred resistance to Cry1Ac and Cry2Ab in field populations of Helicoverpa armigera and H. punctigera. An F2 screen technique was employed that enabled the calculation of the frequency of alleles that confer resistance, and importantly, enabled the detection of recessive alleles. No instances of resistance were detected among 68 alleles scored for Cry1Ac and Cry2Ab in H. punctigera. Similarly, no instances of resistance to Cry1Ac were detected among 416 alleles scored for H. armigera. For this species, 95% confidence intervals around the zero determine that Cry1Ac resistance alleles would not be more common than a frequency of 0.0088. Thus despite the deployment of Ingard® for seven seasons, Cry1Ac resistance remains rare.

However, a surprising result was that resistance to Cry2Ab, the second toxin present in Bollgard II®, is relatively common. For H. armigera, three instances of resistance to Cry2Ab were isolated from 416 alleles examined. Preliminary analyses suggest that all three isolates represent mutations at the same locus. While the F2 technique was expected to identify ‘resistant alleles’ if a sufficient number were tested, the expectation was that prior to the deployment of Bollgard II®, Cry2Ab resistance would be at a frequency approaching the mutation rate, say 10 -5 to 10 -8.

With the imminent wide-scale deployment of Bollgard II®, it was important to assess the magnitude of the threat posed to Bollgard II® by the previously unsuspected resistance to Cry2Ab. Unlike the situation for Cry1Ac resistance, where resistant alleles are rare, for the more common Cry2Ab resistance it was important to examine the fitness of both heterozygotes and homozygotes. Laboratory analyses performed in CSE108C have shown that Cry2Ab resistant insects are fully susceptible to Cry1Ac. Thus it is not surprising that early in the season all larvae struggled on Bollgard II®. However later in the season when titres of Cry1Ac presumably had declined, homozygous Cry2Ab resistant larvae (but perhaps not heterozygous larvae) exhibited enhanced growth on Bollgard II® relative to susceptible insects. Thus although the resistance appears to be functionally recessive on Bollgard II®, opportunities exist for the homozygote to be favoured. Together these results suggest that this form of resistance may inpact on the longevity of Bollgard II®.

The significance of transgenic cotton in the pest control strategy adopted by the

Australian industry makes the management of resistance to the Cry1Ac toxin of Bacillus

thuringiensis essential. Accordingly, the CRDC supported the selection of resistance in

H. armigera so that the extent and nature of the threat could be estimated before it

actually occurred in the field.

During selection of the original H. armigera strain (BX) in which Bt resistance was first

detected, resistance rose to 300-fold and then declined to stabilise at approximately 80-

fold. To assess whether the decline in resistance was due to a loss in general vigour

associated with inbreeding or rather was the result of fitness costs associated with the

resistance, the BX strain was outcrossed to a susceptible laboratory strain and re-selected as the IS strain. With increasing selection pressure, the IS strain reached a resistance

ratio exceeding 800-fold. It was clear from this experiment that the decline in resistance

of the BX strain was the result of inbreeding. However, it was not clear whether the very

high resistance detected in the IS strain was merely the result of improved vigour. As

higher levels of resistance in Cry1Ac-resistant diamondback moth can be associated with

more than one resistance gene (Ferr6 and Van Rie, 2002, Ann. Rev. Entomol . 47, 501-

503), the higher resistance in H. armigera might similarly be indicative of the presence

of a secondary resistance gene (or genes). It is important that we understand all the

resistance options available to H. armigera because we cannot be certain that the order in

which resistance genes arise will be the same in the field as in the laboratory.

Fitness cost associated with resistance is an important factor in determining the

parameters required for an effective refuge strategy. When the fitness of the BX strain

was assessed against a susceptible laboratory strain, we recorded a significant delay in

development that might impede the efficiency of the resistance strategy. However, it

would not be reasonable to rely too heavily on these data because of the different genetic

backgrounds of the resistant and susceptible lines used in that experiment. We

backcrossed the resistance allele into the susceptible line so that we now have resistant

(ISOC) and susceptible lines that share a common genetic background, to the extent that

they are >93% genetically similar. We are, therefore, now in a much better position to

assess the fitness cost associated with the lower level of resistance to Cry 1Ac in

.

Cotton aphid (Aphis gossypii Glover) is a late season pest of cotton, with the potential to

reduce the value of lint by contaminating it with sticky honeydew secretions. Recently, cotton

aphid emerged as a threat during the early and mid season - due to its potential to cause yield

loss and its role as a vector of the disease 'Cotton Bunchy Top'(CBT). This project aimed to

improve understanding of the ecology of this pest, especially season abundance and

overwinter host use, and of its distribution on cotton, which is important in developing

sampling techniques. This project was complemented by two other CRDC funded projects;

'Aphid bio-control' (DAQI 19C), and 'Incorporating aphids, insecticides and early season

plant compensation in PM' (CSP147C). Key outcomes are:

1. Cotton aphid is a mid-late summer pest. A wide range of summer and winter hosts were

identified and included a range of broad leaf weeds, crops and garden plants. Among the

winter crop hosts are faba beans and lupins, although aphid do poorly on them. Aphids

failed to persist on vetch, canola or lucerne. In particular ratoon cotton will carry-over

aphid populations, which is a problem for resistance management and for carry-over of

CBT. This led to recommendations for good overwinter field hygiene.

2. It is likely that winter conditions affect the size of the overwintering populations, with

drier conditions supporting fewer hosts and lower overwinter aphid populations.

3. Cotton aphid uses hosts in farm and urban gardens through winter. Farm gardens in

particular can serve as reservoirs for insecticide resistant cotton aphids and are particularly

important in dry years when other hosts are scarce.

4. The seasonal abundance and host range of cowpea aphids was documented. This species

has two peaks in abundance, in early spring and autumn. It also uses a wide range of hosts,

but is particularly noticeable on medics.

5. Green peach aphid is a cool season specialist. It has a narrower host range than cotton

aphid and cowpea aphid, but uses some brassicaceous hosts that are widespread.

6. A wide range of other aphid species and their hosts was also recorded. This information

has proven valuable, for instance in warning industry of influxes of Rhopalosiphum spp.

which settle on seedling cotton, but which will not establish and breed. This led to the

recommendation not to treat aphid populations unless it is clear they are breeding.

7. Cotton aphids show a preference for the upper canopy leaves of plants. However, at higher

numbers there is a significant population found in the lower canopy. This population is

difficult to reach with insecticides and may be a major source of recolonisation of plants

following insecticide application.

8. Cotton aphid shows a highly clumped distribution, a product of their biology, whereby

females produce live young that do not move far away from the parent. This makes

sampling more difficult as populations may be missed.

9. There is a curvilinear relationship between the proportion of plants infested with aphids

and the mean number of aphids per leaf. This may be useful if it can be linked effectively

with the thresholds being derived in another project.

Outcomes of this research have been widely reported to industry. Future research on aphids

could emphasise selective control, improved understanding of colonization and spread in

cotton, contribution of trap crops or relay crops as hosts and link with spread of CBT.

My presentation today is titled "Marketing our Product". I intend to briefly discuss the markets for Australian cotton, the market outlook for our cotton, make come comments on our crop quality this year and then outline some challenges that I see for our industry.

Irrigated cotton growers stand to make substantial savings in fuel and greenhouse gas emissions in tractor operations if appropriate tractor engine and ground speeds are used and tillage depth is kept to the shallowest that is suitable for the task.

Lifting and moving water around farms with pumping systems for irrigation consumes plenty of energy as water is a heavy liquid. Every litre of water has a mass of one kilogram. A cubic metre of water has a mass of 1000 kg, or a tonne, and a volume of 1000 litres. A Megalitre (ML) has a mass of one million kilograms or one thousand tonnes.

Moisture at picking has a significant impact on cotton's fibre quality. It can lead to colour degradation (spotting) and discoloration which affects the colour grade: the fibre becomes yellower and less bright with the trash sticking to the lint. It can also impact seed quality, with more moisture equaling less germination and vigour.

Surveillance and sampling for Verticillium wilt defoliating strain. Includes diagnosis request forms

Farms are a fantastic place to raise a family, but they can also be dangerous, as unlike most other homes, they are also our workplaces. Help keep our most important resource - our people - safe.

Season report - end of October 2014