Blood digestion in the mosquito, Anopheles stephensi: the effects of Plasmodium yoelii nigeriensis on midgut enzyme activities

N. JAHAN a1p1, P. T. DOCHERTY a2p2, P. F. BILLINGSLEY a2c1 and H. HURD a1
a1 Centre for Applied Entomology and Parasitology, Department of Biological Sciences, Keele University, Staffordshire ST5 5BG
a2 Department of Zoology, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ


Midgut proteases contribute to the success or failure of Plasmodium infection of the mosquito. This paper examines the reciprocal effect of Plasmodium yoelii nigeriensis on midgut trypsin, chymotrypsin, aminopeptidase and carboxypeptidase in the mosquito Anopheles stephensi. The total protein ingested and the rate of protein digestion were unaffected by the parasite, but more protein was ingested at the first than the second bloodmeal. All peptidases were unaffected by the presence of the parasite during the first gonotrophic cycle, when ookinetes were penetrating the midgut. In the second gonotrophic cycle, trypsin and chymotrypsin were unaffected by growing oocysts, but aminopeptidase activity was reduced in the midguts of infected mosquitoes. Chymotrypsin activity was depressed and aminopeptidase activity elevated during the second gonotrophic cycle. Plasmodium infection has a negligible effect on bloodmeal digestion and does not limit the availability of the protein for egg production. The significance of changes in aminopeptidase activity when oocysts are present is discussed.

(Received May 6 1999)
(Revised June 29 1999)
(Accepted June 29 1999)

Key Words: Plasmodium; Anopheles stephensi; trypsin; chymotrypsin; aminopeptidase; bloodmeal.

c1 Corresponding author: Department of Zoology, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, UK. Tel: +44 1224 272 882. Fax: +44 1224 272 396. E-mail:
p1 Current address: Lahore College for Women, Lahore, Pakistan.
p2 Current address: Medical Entomology Section, Laboratory for Parasitic Diseases, NIAID/NIH, Bethesda, MD 20892-0425, USA.