Effects of neem on adults of Eretmocerus warrae (Hym., Aphelinidae), a parasitoid of Bemisia tabaci (Hom., Aleyrodidae) in tropical horticulture systems.

摘要

Side effects of two commercial neem products, NeemAzal-T/S (1% azadirachtin) as foliar application and NeemAzal-U (17% azadirachtin) as soil application were tested in laboratory bioassays against about-to-emerge adults and adults of an aphelinid, Eretmocerus warrae (EW) an efficient parasitoid of the whitefly Bemisia tabaci (WF) in Thailand. Hatching rates of unparasitised WF were reduced by foliar treatments with NeemAzal TS from 84% (control) to 16% (10 ml l-1), by soil application with NeemAzal-U from 84% (control) to 63% (3.0 g l-1). Parasitoid emergence was affected in a dose-dependent manner. Whereas 80% of the EW adults hatched in tap-water treated controls after foliar treatments of pupa with NeemAzal-T/S hatching rates decreased to 50 and 24% at 5 and 10 ml l-1 dose rates respectively. In contrast, the soil application of NeemAzal-U did not affect the emergence of parasitoids. In both neem treatments longevity of the hatched adults was the same for both sexes, and no alternation in sex-ratio was detected. The longevity of the adult parasitoids was only affected after 36 hrs contact with high dose residues of NeemAzal-T/S (10-15 ml l-1) in a dry-residue bioassay test. The experiments indicate that ecto-endo parasitoids are principally highly vulnerable to neem but show in addition that soil application could reduce negative side effects compared to plant spraying and hence improve selectivity.