COMPARATIVE TOXIC ACTIVITY OF FOUR ALGAE, AGAINST THE 2ND AND 4TH LARVAL INSTARS OF BLACK CUTWORM, AGROTIS IPSILON (HUFNAGEL)

Abstract

The dry biomass of four cyanobacterial microalgal strains Anabaena flos aquae, Anabanea laxa, Anabanea fertilissima and Nostoc muscorum was evaluated in invitro assay as a biopesticides against 2 nd and 4 th instars of Agrotis ipsilon. Larvae were fed on leaf discs painted with the algal solution for 24h. The 2 nd instar larvae were more susceptible than the 4 th ones to the four tested algal treatments. N. muscorum treatment was the most toxic one against the 2 nd and 4 th larval instars. Where, its LC 50 values were 45 and 150 mg/ml, respectively while, A. fertilissima was the least one, its LC 50 values were 250 and 660 mg/ ml, respectively. All the treated larvae were susceptible to four tested algal treatments and its resistance varied according to the larval instars and tested alga. Marked decrease in pupation for both 2 nd and /or 4 th instar by the four algal treatments, whereas, the 2 nd instar treated with N. muscorum alga exhibited the most suppressive decrease to 44%, as compared to control (97%). Significant reduction for pupal weight, where, 4 th instar treated with A. flos aquae alga recorded the highest pupal weight decrease to average 290mg, as compared to 484mg of control. Besides prolonging pupal duration where, treatment for both instar with A. flos aquae and A. laxa algae induced the longest period and increased the pupal malformation These results are similar with those obtained by Aly and Abdou (2010) who found that the treatment of Spodoptera littoralis larvae with 5% conc. of Spirulina cells content and cell wall decreased significantly the larval and pupal weight. In contrary with those obtained by Venkatesh et al. (2009) who found that Spirulina increased the weight of pupa and shell of Bombyx mori, which produced by the treated larvae.