Final Report - Rhizosphere biological functions as influenced by GM cotton

The aims of the trial were: 1. To determine whether mating of H. armigera could be disrupted in cotton by mass release of pheromones; 2. If mating disruption was achieved, to determine the effects of this on the densities of eggs and larvae; 3. To observe the nocturnal behaviour of moths in pheromone treated and untreated fields in an attempt to understand the mechanics of mating disruption

Functional soil systems

Final Report - Study of alternaria leaf spot on cotton in Northern Australia

In Australia the two-spotted spider mite, Tetranychus urticae Koch, is regarded as a major pest of cotton. However, neither the pest status nor the ecology of spider mattes on cotton has been studied. Consequently management strategies are based on information derived elsewhere, which may not be relevant in Australia. Therefore the pest status of mites, their patterns of distribution and abundance on cotton and associated host plants, and the factors that influence these patterns were investigated. This project produced a large amount of information from a wide range of experiments. Rather than detail experimental methods, presentation is restricted to the key findings and their implications for mite ecology and management.

Nutrition group activities

This study determined the genetic basis of pyrethroid resistance in Heliothis armigera and characterised those factors that lead to cyclical fluctuations in the frequency of resistance in field populations. The major findings were:

(1) A single major semi-dominant gene, associated with mimed function oxidases, is responsible for most pyrethroid resistance in field populations.

(2) The nerve insensitivity mechanism, which appeared to be important in field failures with pyrethroids in the early 1980's, no longer contributes significantly to the expression of resistance in field populations.

(3) Field application rates kill resistant larvae < 4-days old.

(4) Very small resistant larvae can survive field exposure to pyrethroids as the pesticide decays or is diluted by plant growth.

(5) Field application rates kill susceptible but not resistant adults.

(6) Pupae overwintering under cotton crops have high levels of resistance and high survival.

These findings have been integrated into the resistance management strategy for control of spring/summer pests in broad acre crops in eastern Australia. In particular, these results led to, or validated, recommendations about the commercial use of pyrethroids:

Use pyrethroids only on larvae < 5 mm,

Do not use pyrethroids at low rates against non-Heliothis pests,

Do cultivate cotton crop stubble to destroy overwintering populations of Heliothis,

Use a synergist, piperonyl butoxide, with pyrethroids to reduce selection pressure for resistance.

The cotton industry is one of the most technologically advanced agricultural industries in Australia. However, advisers to cotton growers often lack confidence in advising their clients on decisions relating to soil management. It was thought that training these advisers would increase their knowledge and skills in soil management, thereby helping to improve and sustain cotton production by reducing soil degradation and lessening the number of expensive ineffective machinery operations in growing cotton. Thus the project was aimed at improving the level of soil management advice given to New South Wales cotton growers by Departmental advisers and private consultants. The project consisted of a series of three soil management workshops, based on the use of backhoe pits and SOILpak, the soil management decision support system for cotton production on cracking clay soils. The workshops were held at yearly intervals in the main cotton growing areas of New South Wales, and involved a total of approximately 50 participants, as follows:

In January 1983, pyrethroids failed to give satisfactory field control of Heliothis (Helicoverpa armigera (Hubner) at Emerald in central Queensland. Prior to that, as in the USA (Riley 1989), they had been "heralded as miracle insecticides" as they replaced the resistance prone and environmentally liable organochlorines, cyclodienes and organophosphates (Morton & Collins 1989). When they were introduced commercially in the late 1970's, they had many benefits over what was then available. They were very cost effective at extraordinarily low rates on a broad range of agricultural and public health pests, had no residue problems, were safe to mammals, had low environmental impact and were immobile in the soil (Elliott 1989). Indeed, they were regarded as the almost perfect insecticide (Leahey 1985). In fact, by 1986, their popularity was such that they accounted for around 25%, of all insecticides used in agriculture and public health (Jackson 1989, Hirano 1989). They were particularly favoured in cotton because of their contact mode of action and good efficacy against previously resistant pests and by the mid 1980's accounted for 49%", of the world cotton insecticides market (Walkinson 1989, Riley 1989). So when the breakdown at Emerald was clearly shown to be due to the development of resistance (Gunning et al 1984), there was no disguising the concern of the Australian cotton industry in particular, but also the other field crop industries in which H. armigera was a key pest. Within 6 months of these reported field failures, a strategy aimed at containing the resistance problem, had been formulated and ratified for use in the following season, by all parties concerned (Forrester 1990)

A technique to identify the host crop of Heliothis moths by analysis of elemental content has been progressively developed over several seasons (CRC Project CS13L, Fin 1986). In this grant period we finalised statistical analyses of the existing database for individuals from known hosts and have developed a procedure for allocating unknown individuals collected in cotton crops to probable hosts (developed by Dr. Richard Motton CSRO Biometry Unit). The procedure (based on Newton's method with gradient matrix calculated by formula) allows for moths to be allocated to one of five major host crops or to a class derived from none of the major crops and includes a facility to use only a subset of possible hosts in an allocation run. The procedure gives acceptably accurate estimates of the proportion of a sample of moths derived from major hosts, though to date it has been validated using the same database as used to produce it. Further data for individuals from known hosts is being collected this season for validation purposes. We have commenced processing elemental data for unknowns collected in 1985/86 using the procedure but have encountered a problem which may be due to dust contamination of field caught moths. The elements Fe, P, and Mn are the most important in discriminating moths from different crops (accounting for 85-90% of the variation), but most of the moths taken from traps show levels of Fe (and Al and Si) outside the range of any of those reared from crops, while levels of other elements are similar to those for moths reared on crops. Elevated concentrations of Fe, Al and Si are characteristic of sample being contaminated with soil, which may easily occurring pheromone traps from which the moths are collected.