Effectiveness of the blue-green algae <i>Anabaena flos-aquae</i> in controlling <i>Helicoverpa armigera</i> (Lepidoptera: Noctuidae)

Abstract

The blue-green algae are known as Anabaena flos-aquae, which is a nutrient-rich food supply. The 2^nd and 4^th larval instars of the cotton bollworm, Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) were tested in a lab using a crude extract of the cyanobacterial isolates of the Anabaena flos-aquae alga. The algal extract was administered to larvae via contact and feeding techniques. Depending on the larval instars and the applying technique, the algal extract's effects changed. Contact algal treatment was more successful than the feeding treatment. Also, the second larval instar was more vulnerable than the fourth. In terms of contact treatment, the LC₅₀ value for the second larval instar was 0.0125 ml/l, while the fourth instar's 0.025 ml/l. In terms of feeding treatment, the LC₅₀ value was 0.05 and 0.1 ml/l for the second and fourth instars, respectively. In contrast to controls, where adults emerged at a rate of 100% compared to 85%- 86% adults emerged as second instar and fourth instar in terms of feeding method, respectively. While adults emerged of second instar and fourth instar in terms of contact method was 81%-93%, respectively. The contact method's LC₅₀ value for the second larval instar caused a highly significant increase in larval and pupal durations and a drop in adult emergence. Also, the contact method's LC₅₀ value for the second larval instar caused the greatest percentage of pupation malformation 37%, and adult malformation (19%). Also, adults that emerged from the contact-treated 4th larval instar showed a significant decrease in egg hatchability to 82.4%. It was found that the proportion of pupation had significantly decreased. Additionally, adult longevity and adult emergence percentage were decreased for contact or feeding treatments on the fourth larval instar .