Field Evaluation of Sunflower Varieties for Susceptibility to the Parthenium Beetle Zygogramma bicolorata

Fifteen varieties of sunfluwer (Helianthus annuus L.) were evaluated under field conditfuns fur their feeding attraction to the Mexican beetle Zygogramma bicolorata Pallister (Coleoptera : Chrysomeltdae), a potential biological control agent of the noxious weed Parthenium hysterophorus L. (Asteraceae). When 500 marked adults were released on one-month-old sunflower plants, 90% of them were observed to move away in une day, 99.2% by the 4th day and 100% by the 7th day. Althuugh upto 4.8l milliun adults were estimated to be present at a time in the 2 ha weed stand surrounding the experimental plot, the numbers that alighted on the sunflower crop were negligible and did not exceed 316 adults on 651 plants. However, slight feeding by adults was noticed on 6 plants for 5 days, after which they moved away. The present studies indicate that sunflower is not a suitable host plant for the beetle and the chances of host shift appear remote.