BIOLOGICAL-ACTIVITY OF NEEM SEED KERNEL EXTRACTS AND SYNTHETIC AZADIRACHTIN AGAINST LARVAE OF PLUTELLA-XYLOSTELLA L

Citation
Rhj. Verkerk et Dj. Wright, BIOLOGICAL-ACTIVITY OF NEEM SEED KERNEL EXTRACTS AND SYNTHETIC AZADIRACHTIN AGAINST LARVAE OF PLUTELLA-XYLOSTELLA L, Pesticide science, 37(1), 1993, pp. 83-91
Citations number
32
Categorie Soggetti
Agriculture
Journal title
ISSN journal
0031613X
Volume
37
Issue
1
Year of publication
1993
Pages
83 - 91
Database
ISI
SICI code
0031-613X(1993)37:1<83:BONSKE>2.0.ZU;2-1
Abstract
The activity of two neem extracts, AZT and NEEM-AZAL (containing 30 an d 3 mg azadirachtin ml-1 respectively) and synthetic azadirachtin (AZ) against second-instar larvae (L2) of Plutella xylostella L. was exami ned using leaf-dip bioassays. On Chinese cabbage, AZ was significantly (P < 0.05) less toxic (3 to 4-fold; LC50 0.54 mug AZ ml-1) than eithe r neem extract against a laboratory strain of P. xylostella (FS). The LC50 values for AZT against the FS and another laboratory strain (Well come) were not significantly different on Chinese cabbage. The activit y of AZT against the FS and Wellcome strains was similar on Chinese ca bbage and Brussels sprout. AZT was significantly less toxic (3-fold) o n Brussels sprout against an acylurea-resistant field strain (Sawi) wh en compared with the FS strain on Chinese cabbage. Larval mortality (a t day 13) was found to increase with increasing exposure time of P. xy lostella (FS) larvae to AZT-treated Chinese cabbage, although there wa s little difference in mortality between 48 and 120 h exposure. When A ZT, NEEM-AZAL and AZ were applied at a dose (1 mug AZ ml-1) which gave end-point mortalities between 50 and 90 % (at day 13), all treatments delayed the development of a proportion of surviving larvae but no mo rphogenetic abnormalities were observed in larvae which reached pupati on. Evidence for antifeedant (reduced weight gain) and repellant effec ts (choice-chamber) for AZT were observed with L2 P. xylostella (Wellc ome) on Chinese cabbage. AZT was also shown to have ovicidal activity against P. xylostella (Wellcome) at relatively high dose ranges (10-10 00 mug AZ ml-1) as well as some contact activity (FS strain) in topica l bioassays. In residual bioassays on glass with adults of the hymenop teran endo-larval parasitoid of P. xylostella, Diadegma semiclausum (I chneumonidae), AZT showed little or no activity at rates up to 1000 mu g AZ ml-1. In medium-volume (MV, 200 litre ha-1) and ultra-low-volume (c. 1 litre ha-1) spray bioassays on Brussels sprout, AZT gave 16-92 % and 88-100 % mortality respectively (Wellcome strain) at rates approx imating to 1-20 g AZ ha-1. The residual activity of AZT and NEEM-AZAL against P. xylostella (FS) on Brussels sprout (MV spray) was observed to decrease appreciably after three days, the decline in activity bein g particularly marked for NEEM-AZAL.