Toxicokinetics of [³H]‐dihydroazadirachtin in the variegated cutworm Peridroma saucia

Abstract

The excretion, retention, and tissue distribution of [3H]-dihydroazadirachtin was investigated in the variegated cutworm, Peridroma saucia (Noctuidae). The candidate compound was rapidly cleared from the hemolymph following either oral exposure or topical administration, with maximum concentrations at 6 h post-treatment and peak appearance of label in the frass at 12 h. However, approximately 45 and 55% of the labelled material was retained in the body at 72 h in respective treatments. Major depots for retained radioactivity were the gut (24% of the administered oral dose, 18.8% of the administered topical dose) and integument (1 2.2% of the oral dose and 30.7% of the topical dose). The variation in tissue distribution of dihydroazadirachtin with respect to the mode of application is discussed. A single polar metabolite fraction was obtained from the frass of dihydroazadirachtin-fed larvae. The physiological and behavioral effects of 22,23-dihydroazadirachtin and azadirachtin are quantitatively similar.

The effect of neem allelochemicals on nutritional physiology of larval Spodoptera litura

“…Thus, this effect is unequivocally independent of its antifeedant properties. However, when S. litura sixth instars were force-fed with leaf discs within 6 h, to consume about 1.2 #g of azadirachtin as described earlier (Koul et al, 1994), growth regulatory effects were observed. We used this procedure in addition to topical and injection methods to demonstrate the reduction in the activity of midgut trypsin, which is a primary protease in the gut in many lepidopteran genera (Broadway & Duffey, 1988), and to show whether the mode of application imparts any variation in this enzyme reduction.…”

“…However, after injection and topical application this activity was reduced to 34% and 37.5% respectively. Toxicokinetic studies of azadirachtin have clearly shown that retention of this allelochemical in the tissues varies with the mode of application (Koul et al, 1994); thus a possible variation in tryptic activity as well. Our findings indicate that decrease in tryptic activity may not be due to direct inhibition of the enzyme and has already been demonstrated in Manduca sexta (Timmins & Reynolds, 1992), So the possibility of the direct action on enzyme secreting cells of the midgut wall or the mechanism which controls trypsin secretion (may be hormonal) is highly probable.…”

“…In terms of nutritional physiology, it has been recently shown with several lepidopteran species that avoid-ance of primary antifeedant activity can be achieved quite easily after applying azadirachtin either topically or by injection (Koul & Isman, 1991). Accordingly evidence is available that insect growth inhibitory and antifeedant effects are independent of each other (Koul et al, 1987(Koul et al, , 1994Koul & Isman, 1991;Timmins & Reynolds, 1992). The effects of azadirachtin on gut physiology are mostly related to efficiency of diet conversion (Ayyangar & Rao, 1989;Timmins & Reynolds, 1992, Peter & Ananthakrishnan, 1993 or inhibition of digestive enzymes.…”

“…(2-4 h-old) were individually administered all the four compounds either orally, topically or via injections. In oral feeding azadirachtin was given at the rate of 1.2 #g; salannin equal to 5.0 #g and nimbinene and nimbin at the rate of 20/~g to each insect by applying the amount to castor leaf discs as described earlier (Koul et aL, 1994). Due to the antifeedant nature of these compounds the larvae were pre-starved for 5 h before the treated leaf discs were provided for feeding to individual larvae with a known quantity of each compound.…”