IMMUNE-DEPRESSION IN RHODNIUS-PROLIXUS INDUCED BY THE GROWTH INHIBITOR, AZADIRACHTIN

Azadirachtin (1.0-mu-g/ml) if fed to last-instar larvae of Rhodnius prolixus through a blood meal, affects the immune reactivity as shown by (i) a significant reduction in numbers of haemocytes and nodule formation following challenge with Enterobacter cloacae B12 (ii) a reduction in ability to produce antibacterial and lysozyme activities in the haemolymph when inoculated with bacteria, (iii) a decreased ability of azadirachtin-treated insects to destroy the primary infection caused by inoculation of E. cloacae cells. However, the present experiments, unlike other immune reactions, fail to demonstrate any interference of azadirachtin with the prophenoloxidase-activating system since the melanin production was not reduced when this system was stimulated by trypsin or by the presence of bacteria in the haemolymph. It is suggested that the immune response is deficient in the azadirachtin-treated insects. The significance of these results is discussed in relation to the general mode of azadirachtin action in insects.