Search

Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae) of Mexican origin, introduced for biological control trials against the weed Parthenium hysterophorus (Compositae), was found to feed on the tender leaves of the related plant sunflower (Helianthus annuus Linnaeus) at a few places in Kolar district in Karnataka State, India. The insects in these populations exhibited variability in feeding response to sunflower under laboratory and field conditions. The sesqueterpene lactone parthenin, specific to P. hysterophorus, was found to induce feeding by the adults of Z. bicolorata on treated sunflower leaves within six hours, as compared to 4–7 days on untreated leaves. Further investigations resulted in the novel finding that dusting of parthenium pollen, or smearing its extract which contains parthenin, on sunflower leaves also induced feeding responses in adults. Parthenium pollen was detected on sunflower leaves growing in close proximity to the weed stand, suggesting that this could be one of the factors influencing variability in the feeding behaviour of Z. bicolorata.

Zygogramma bicolorata Pallister was introduced for biological control trials against the weed Parthenium hysterophorus (Asteraceae) in India. The insect entered diapause over an extended period of time between July and December in Bangalore. Diapausing adults burrowed into the soil, and emerged in May–June with the commencement of monsoon rains. Percentage diapause increased over time, peaking at 72% during November. Non-diapausing adults were capable of breeding, under laboratory conditions, during the winter. Some adults bred both before and after diapause, during two consecutive years. Soil moisture played an important role in providing the conditions for burrowing or emerging from the diapause chambers. The studies also showed that diapausing adults had to be exposed to the high summer temperatures, for termination of the diapause. It was possible to break diapause by continuous exposure to 30°C, 35°C and 40°C for 22 days, nine days and 10 hours, respectively, during February–March, about three months after its inception. This method can be used to initiate mass multiplication for carrying out releases early in the season.