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.

Graphical abstractMicroscopy studies on the invasion of cattle ticks (Rhipicephalus microplus) and sheep blowflies (Lucilia cuprina) by Metarhizium anisopliae reveal different patterns of incursion.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The invasion of two different hosts by Metarhizium anisopliae was studied using LM and SEM. ► Cattle tick invasion was characterised by cuticle destruction as well as surface hyphal growth. ► Adult Sheep blowfly invasion appeared to occur through the buccal cavity not the outer cuticle. ► Large numbers of un-germinated spores were seen adhering to the outer blowfly surfaces.