Morphological observations of haemocytes from Agrotis ipsilon (Lepidoptera: Noctuidae) larvae infected by Escherichia coli.

Understanding the types of haemocytes involved in the immune response in insects, and the mechanism involved in determining that response, can provide a scientific reference for developing effective microbial insecticides. Therefore, the current study examined haemocytes from Agrotis ipsilon (Hufnagel) larvae infected with Escherichia coli in terms of their morphology, total counts, and relative proportions at different time points post-infection by optical microscopy technology. The results revealed six types of haemocytes (prohemocytes, plasmatocytes, granulocytes, spherule cells, oenocytoids, and cystocytes) in the haemolymph of sixth-instar larvae. Haemocyte deformation, disruption, nuclear changes, and vacuoles were recorded after infection with different dosages of E. coli. At each time period post-infection, the total haemocyte count was significantly higher than in the controls, peaking at 24 h post-infection and then decreasing by 48 h post-infection. The proportion of prohemocytes decreased significantly until 24 h post-infection, and then began to increase. By contrast, the proportions of plasmatocytes, granulocytes, spherule cells, oenocytoids, and cystocytes relatively increased, and peaked by 24 h post-infection, and then decreased. This revealed that strong immune response was stimulated in larva of A. ipsilon in a short time after infection with E.coli, and the results shed addition light on the cellular immune response of insects to pathogens. [ABSTRACT FROM AUTHOR]