SummarySirodesmin PL is a phytotoxin produced by the fungus Leptosphaeria maculans, which causes blackleg disease of canola ( Brassica napus ). This phytotoxin belongs to the epipolythiodioxopiperazine (ETP) class of toxins produced by fungi including mammalian and plant pathogens. We report the cloning of a cluster of genes with predicted roles in the biosynthesis of sirodesmin PL and show via gene disruption that one of these genes (encoding a two-module non-ribosomal peptide synthetase) is essential for sirodesmin PL biosynthesis. Of the nine genes in the cluster tested, all are co-regulated with the production of sirodesmin PL in culture. A similar cluster is present in the genome of the opportunistic human pathogen Aspergillus fumigatus and is most likely responsible for the production of gliotoxin, which is also an ETP. Homologues of the genes in the cluster were also identified in expressed sequence tags of the ETP producing fungus Chaetomium globosum . Two other fungi with publicly available genome sequences, Magnaporthe grisea and Fusarium graminearum , had similar gene clusters. A comparative analysis of all four clusters is presented. This is the first report of the genes responsible for the biosynthesis of an ETP.

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Cotton or melon aphid, Aphis gossypii Glover, is an important pest of cotton, and recently the neonicotinoid group of insecticides has provided a key option for control where they are used as seed treatments and foliar sprays. Here we document for the first time in Australian cotton, resistance to three neonicotinoids (acetamiprid, clothianidin and thiamethoxam) in A. gossypii via diagnostic discriminating concentration assays that were also associated with field control failure. Subsequent full log dose probit analysis on strains with discriminating dose survivors confirmed acetamiprid, clothianidin and thiamethoxam resistance at 6.4-, 10-and 22-fold, respectively. Further laboratory pressuring of strains caused acetamiprid resistance to significantly increase to 22-fold but resistance factors to clothianidin and thiamethoxam were unchanged. Clearly there is a need to reduce overall neonicotinoid selection to prevent or slow any increase in neonicotinoid resistance. An effective method to contain resistance would be to move away from the more persistent neonicotinoid seed dressings to either organophosphate or carbamate-based products and to limit the use of neonicotinoid foliar sprays.

The Australian cotton industry progressively embraced integrated pest management (IPM) to alleviate escalating insecticide resistance issues. A systems IPM approach was used with core principles that were built around pest ecology/biology and insecticide resistance management; together, these were integrated into a flexible, year-round approach that facilitated easy incorporation of new science, strategies, and pests. The approach emphasized both strategic and tactical elements to reduce pest abundance and rationalize decisions about pest control, with insecticides as a last resort. Industry involvement in developing the approach was vital to embedding IPM within the farming system. Adoption of IPM was facilitated by the introduction of Bt cotton, availability of selective insecticides, economic validation, and an industry-wide extension campaign. Surveys indicate IPM is now embedded in industry, confirming the effectiveness of an industry-led, backed-by-science approach. The amount of insecticide active ingredient applied per hectare against pests has also declined dramatically. Though challenges remain, pest management has transitioned from reactively attempting to eradicate pests from fields to proactively managing them year-round, considering the farm within the wider landscape.

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. l egg per day). Consumption by first instar F. schultzei was much lower than for second instars. Adult T. tabaci consumed ca. l 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.

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