Biomedical Engineering Reference
In-Depth Information
with appressorium b. Scanning electron micrograph showing appressoria (1) in and
around a setal socket (2) on the insect cuticle c. diagrammatic representation of conidial
germination on an insect cuticle. diagrammatic representation of structure of insect
cuticle and mode of penetration (according to Clarkson and Charnley 1996).
the insect cadaver (mycosis) and fi nally sporulates profusely on it
(Fig. 2)
(fi gure legend: Mycosis induced by the insect pathogenic fungus
Beauveria
bassiana
on cadavers of insects dead due to infection. (a) silk worm (b) and
(c) tobacco caterpillar larva and egg mass (d) brinjal beetle (e) cereal beetle
(f) pea aphid (g) sorghum shoot borer (h) cockroach (i) cotton boll worm
(j) blister beetle). The spores on the cadaver are dispersed to start a second
infection cycle on the insects that are yet to be infected. The fungus can
attack egg masses and also sproulate on the pupa when the infected larva
metamorphoses into pupa. The infection process is demonstrated in fi gure
3
(Figure legend: Life cycle of an entomopathogenic fungus in the insect
host—the process of infection). Every step in the pathogenic life cycle of
the fungus is gene controlled. During the past decade, the battery of genes
operating at each step and the important (main) genes are being unraveled.
Recently an arsenal of molecular biology techniques is being utilized
for the study of pathogenicity genes in these fungi. These include study of
transcriptomes through microarray, suppression subtractive hybridization
(SSH) (Zhang and Xia 2009), quantitative real time PCR (qRT PCR) (Fang and
Bidochka 2006), expressed sequence tag (EST) library from fungi cultured
in vitro
on cuticle extracts and
in vivo
in insects (Freimoser et al. 2003, Wang
