Ecology of red scale (Aonidiella aurantii (Maskell) [Hemiptera: Sternorrhyncha : Diaspididae]) in citrus orchards on the Central Coast of New South Wales

Abstract

I used pheromone traps over the three seasons to show that the scale has three annual generations in the region, with spring peaks of male flights occurring between 20 September and 20 October, summer peaks between 20 December and 20 January, and autumn peaks between 20 February and 30 March. Cold weather in winter, particularly ambient temperatures at sunset and sunrise, influenced scale phenology and scale mortality. I derived a positive correlation between numbers of male scale trapped in summer generations with those trapped in the preceding winter/spring generation. I recorded five parasitoids, several predators and six entomopathogens of the scale. A native coccinellid beetle, Halmus chalybeus, appeared to be the most important natural enemy in the region. There was no evidence of competitive displacement among parasitoid species. I found no evidence of density-dependency relationships between the scale and its parasitoids, or between the scale and Halmus chalybeus. I rarely observed intraguild predation of Aphytis species on Encarsia species. In a field experiment in which I prevented Iridomyrmex rufoniger from foraging on honeydew produced by black scale (Saissetia oleae), I showed that the ant disrupted the activities of five red scale parasitoids (Aphytis chrysomphali, Aphytis melinus, Encarsia citrina, Encarsia perniciosi and Comperiella bifasciata) and two predators (Halmus chalybeus and Rhyzobius lophanthae, another native coccinellid). I also observed selfasphyxiation of black scale by its honeydew in the absence of Iridomyrmex rufoniger. The ant did not disrupt predation on red scale by Orcus australasiae, also a native coccinellid. My molecular studies on yellow scale confirmed a recent (2006""2007) record of it being present in an important inland citrus producing region of the state where it had not been previously recorded. My molecular results for species of Aphytis species showed that Aphytis chrysomphali and Aphytis melinus occur in citrus orchards on the Central Coast of New South Wales: Aphytis lingnanensis, which occurs in Queensland, was not recorded. I recorded molecular differences between specimens of Aphytis. These differences, which were associated with variation in pigmentation of pupae, suggested that Aphytis melinus may have been introduced on more occasions than officially recorded, and from two sources, not one. My molecular results for the Encarsia species suggested that the form of Encarsia citrina parasitising armoured scales in coastal citrus orchards of New South Wales may be a native or Australasian strain, or from Southeast Asia. There are no formal records of Encarsia citrina being successfully introduced to Australia, and the form I recorded was genetically different to a University of California, Riverside accession. The six species of entomopathogens comprised Microcera coccophila, Microcera larvarum, Tetracrium coccicolum, Tetracrium novae-zealandiae, Clonostachys coccicola and Myriangium citri. I obtained, for the first time, pure cultures from single spores of each species. My field observations indicated that they all play roles in the biological control of armoured scale in the region. I confirmed, for the first time, that Microcera coccophila and Microcera larvarum are entomopathogens of armoured scale, by fulfilling the Koch's postulates in laboratory bioassays. Published records I reviewed during my studies suggested the presence of Microcera coccophila, Tetracrium coccicolum and two unidentified species in eastern Australia. One of these may have been Myriangium citri, specimens of which are in the Plant Pathology Herbarium, Orange, New South Wales. Microcera larvarum may have been recorded as another species, but I found no records of Tetracrium novae-zealandiae and Clonostachys coccicola being previously recorded in Australia. My study also represents the first occasion on which the anamorph of Tetracrium novae-zealandiae has been recorded and described.

Date of Award	2012
Original language	English