The effect of azadirachtin on the midgut histology of the locusts, Schistocerca gregaria and Locusta migratoria

The effects of azadirachtin on midgut cells of adult Schistocerca gregaria and Locusta migratoria were investigated by both light and electron microscopy. Pathological effects were seen in both species which could be related to dose and time after treatment. The midgut cells showed a slow necrosis, a rounding up of the cell and swelling of organelles; the nidi were reduced in size and number, the connective tissue beneath the epidermal layer became enlarged with many invading cells/nuclei and the circular and longitudinal muscles become rounded and swollen. The pathological effects were closely linked to a loss of feeding, with injections of 5, 10 and 15 mug/g azadirachtin causing an increasingly rapid onset of the effects associated with an increasingly reduced food intake. At the highest dose, full histopathological effects were seen at 8 hr and death occurred after 3 days. At 1 mug/g, however, the insects showed midgut disruption and reduced feeding by day 3 post-treatment but both feeding and gut pathology had recovered by day 7. At all times, histopathological effects were different from those in starved insects.