IPM program for the macadamia industry – University of the Sunshine Coast

Andrew Hayes

This project is part of a larger IPM program (MC16003-8) and investigated behavioural and electrophysiological responses of insects to odours identified in conjunction with NSW DPI. Macadamia have a wide variety of insect pests, some of the most significant are the macadamia seed weevil (Kuschelorhynchus macadamiae), the fruitspotting bug (Amblypelta nitida) and Leptocoris rufomarginata. Initial studies focused on K. macadamiae and response to odours from macadamia. Unsurprisingly, both large and small nuts attracted the weevils in olfactometer studies, although none of the more volatile compounds from the headspace and solvent extractions showed behavioural responses. On the other hand, key fatty acids (e.g. myristic acid, palmitoleic acid) are attractive to the weevils. These are the fatty acids that are higher in immature nuts. As nuts mature, their fatty acid profile changes, and become dominated by other acids (such as oleic acid). Weevils avoid the odour of this acid. Pure palmitoleic acid is expensive, and so an alternative source of this acid was found in commercially available sea buckthorn oil. A series of field trials were run, at the CTH, Alstonville. These trials tested macadamia oil spiked with a variety of fatty acids and at various times of year. No weevils were trapped in any of these trials. A recent APVMA permit allowing the use of indoxacarb (PER86827) to control the pest have lessened the urgency to control this pest. Fruitspotting bug (A. nitida) is a major pest of macadamia. The banana spotting bug (A. lutescens lutescens) has commercial lure for its control based on an aggregation pheromone, and so A. nitida may also use such a strategy. The pheromone in A. lutescens lutescens is produced by the male and has been shown to attract both male and female bugs. When kept in culture with males, female fruitspotting bugs avoid the odour of groups of males, but not if females are kept in same-sex enclosures for several days - suggesting a male-produced odour that allows females to make decisions about behavior. Females are not attracted to the odours of a single male bug, suggesting that multiple males are needed before the putative pheromone is produced, perhaps in a mating lek. Aerations of were made of unmated A. nitida bugs individually and in groups. The only odours detected were those that have been reported previously, and do not show any behavioural or electrophysiological responses in previous trials associated with this project. No pheromones or attractant odours are known for Leptocoris bug but other genera in the family produce odours containing monoterpenes; aerations above groups of Leptocoris bugs showed monoterpenes. Y-tube olfactometer assays determined that the bugs either avoided or ignored most of the compounds when tested individually, but when blended in the same relative proportions as found in the headspace over live bugs, they were significantly attracted to the blend. Electrophysiological studies with antennae showed clear detection of several of the major components of the blend. Field tests were conducted to test this blend in the field, but no bugs were trapped.

IPM program for the macadamia industry – University of the Sunshine Coast

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