Toxicity Bioassays of Essential Oils against Hadda Beetle Henosepilachna vigintioctopunctata (F)

Contact, repellent and antifeedant bioassays of essential oils (EO’s) viz., basil oil and citronella oil were evaluated against hadda beetle Henosepilachna vigintioctopunctata (F) in brinjal. Based on the results of leaf dip bioassay, the LC50 and LC90 values of basil oil and citronella oil were 1.25% and 2.85%, 0.93% and 1.52%, respectively at 24 hrs after treatment (HAT). While the corresponding LC50 and LC90 values at 48 HAT were 0.85% and 1.70%, 0.63% and 1.14%, respectively. Repellent and antifeedant effect of the chosen essential oils were also evaluated by modified preference method and no choice method, respectively. At 0.5 to 1% concentration, both basil and citronella oil showed 90-100% repellence at 30 and 60 min of treatment. 100% antifeedant effect was also observed at the same concentration (0.5 to 1%) for both the EO’s at 24 HAT. GC-FID/GC-MS analysis of basil and citronella oil revealed that the predominant component of basil oil was methyl chavicol (75.73%), followed by linalool (18.21%) and cuprenene (1.58%); in citronella oil, geranial (64.77%) was the most predominant component followed by citronellyl acetate (7.92%), geraniol (7.08%), (Z) iso citral (5.29%) and neral (3.60%).