Tissue-Specific Incorporation of Azadirachtin in the Malpighian Tubules of Locus ta migratoria

The retention, tissue distribution, and localization of [22,23-3H2]dihydroazadirachtin A was investigated in the female locust, Locusta migratoria. A constant quantity of 0.4 to 0.5 μg of dihydroazadirachtin A per gram body weight is recovered in the unchanged form 5 days after injection of any of the physiologically effective doses in the range of 1.5 to 3.0 pg/g. Malpighian tubules account for 73.7% of the amount of dihydroazadirachtin A which is retained in the whole body. In the Malpighian tubules it is localized in the basal and inner regions. It is inferred from these results, that dihydroazadirachtin A acts in its unchanged form through a high-affinity binding to organ-specific membrane receptors.