Laboratory studies on Australian isolates of Metarhizium anisopliae as a biopesticide for the cattle tick Boophilus microplus

Thirty-one isolates of Metarhizium anisopliae were bioassayed against the cattle tick (Boophilus microplus). More than half of the isolates showed a high degree of virulence to ticks. Radial growth curves for growth between 20 °C and 40 °C were obtained for all isolates. This information together with information on virulence will be important for the selection of isolates suitable to kill ticks on the surface of cattle. A biopesticide for cattle ticks must kill ticks rapidly at temperatures within the upper end of most isolates' growth curves. It was also found that the time taken to achieve 100% tick mortality in vitro using a virulent isolate could be halved by applying conidia in a 10% oil emulsion. Scanning electron microscopy and light microscopy were used to investigate and compare the germination and penetration of conidia formulated in aqueous and oil formulations. It was found that conidia in both formulations were able to germinate and produce appressoria on the surface of ticks in less than 11 h. Marked weakness within 26 h, followed by extensive hyphal growth on the cuticle characterised the invasion of ticks by M. anisopliae.

Pen studies on the control of cattle tick (Rhipicephalus (Boophilus) microplus) with Metarhizium anisopliae (Sorokin)

Three field trials were conducted over 12 months to assess the pathogenicity of Metarhizium anisopliae to parasitic stages of Rhipicephalus (Boophilus) microplus on dairy heifers under different environmental conditions. Two isolates were selected based on their high optimal growth temperature (30 °C), good spore production characteristics and ability to quickly kill adult engorged ticks in the laboratory. Spores were formulated in an oil emulsion and applied using a motor driven spray unit. Surface temperatures of selected animals were monitored, as were the ambient temperature and relative humidity. Unengorged ticks sampled from each animal immediately after treatment were incubated in the laboratory to assess the efficacy of the formulation and application. Egg production by engorged ticks collected in the first 3 days after treatment was monitored. Side counts of standard adult female ticks were conducted daily, before and after treatment to assess the performance of the fungus against all tick stages on the animals. In each trial the formulation rapidly caused 100% mortality in unengorged ticks that were removed from cattle and cultured in the laboratory. A significant reduction in egg production was recorded for engorged ticks collected in the 3 days post-treatment. However, there was little effect of the formulation on the survival of ticks on cattle, indicating that there is an interaction between the environment of the ticks on the cattle and the biopesticide, which reduces its efficacy against ticks.

Studies on the rust Prospodium tuberculatum, a new classical biological control agent released against the invasive alien weed Lantana camara in Australia. 2. Host range

A strain of the rust Prospodium tuberculatum from Brazil was screened as a potential biocontrol agent against 40 Australian Lantana camara forms and 52 closely related, non-target plant species. Results under glasshouse conditions showed that the Brazilian rust strain is pathogenic to only two flower colour forms: pink and pink-edged red. Macro- and microsymptoms were recorded using 11 assessment categories and four susceptibility ratings. No macrosymptoms were observed on any of the non-target plants.

Comparative studies on the invasion of cattle ticks (Rhipicephalus (Boophilus) microplus) and sheep blowflies (Lucilia cuprina) by Metarhizium anisopliae (Sorokin).

Microscopic investigations over time were carried out to study and compare the pathogenesis of invasion of ticks and blowflies by Metarhizium anisopliae. The scanning electron microscope and stereo light microscope were used to observe and record processes on the arthropods' surfaces and the compound light microscope was used to observe and record processes within the body cavities. Two distinctly different patterns of invasion were found in ticks and blowflies. Fungal conidia germinated on the surface of ticks then hyphae simultaneously penetrated into the tick body and grew across the tick surface. There was extensive fungal degradation of the tick cuticle, particularly the outer endocuticle. Although large numbers of conidia adhered to the surface of blowflies, no conidia were seen to germinate on external surfaces. A single germinating conidium was seen in the entrance to the buccal cavity. Investigations of the fly interior revealed a higher density of hyphal bodies in the haemolymph surrounding the buccal cavity than in haemolymph from regions of the upper thorax. This pattern suggests that fungal invasion of the blowfly is primarily through the buccal cavity. Plentiful extracellular mucilage was seen around the hyphae on tick cuticles, and crystals of calcium oxalate were seen amongst the hyphae on the surface of ticks and in the haemolymph of blowflies killed by M. anisopliae isolate ARIM16.

Host specificity studies on Gynaikothrips (Thysanoptera: Phlaeothripidae) associated with leaf galls of cultivated Ficus (Rosales: Moraceae) trees

Host specificity tests on Gynaikothrips ficorum (Marchal) and Gynaikothrips uzeli (Zimmerman) (Thysanoptera: Phlaeothripidae) have shown that under experimental conditions, G. ficorum will induce leaf galls on both Ficus benjamina L. and Ficus microcarpa L. f. (Rosales: Moraceae), but G. uzeli will induce galls only on F. benjamina. A further interesting aspect of the results is that gall induction by G. uzeli on F. benjamina appears to have been suppressed in the presence of F. microcarpa plants in the same cage. Liothrips takahashii (Moulton) (Thysanoptera: Phlaeothripidae), an inquiline in the galls of these Gynaikothrips, is reported for the first time from Australia, mainland China, Malaysia, Costa Rica, and western USA.