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Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae), a biological control agent of Parthenium hysterophorus L. (Asteraceae), was feeding on leaves of Helianthus annuus in India, raising concerns of its host range. Based on the age grading technique, it was shown that the majority of Z. bicolorata on sunflower plants at any time were reproductively immature. This establishes that Z. bicolorata does not pose any risk to sunflower in India.

Freshly emerged adults of Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae), introduced for biological control trials against the noxious weed Parthenium hysterophorus , were seen to feed and lay eggs on sunflower leaves under confined conditions in the laboratory. The time taken for initiation of feeding was found to be positively correlated with adult age, while survival after feeding on the crop was negatively correlated. However, adults that had fed on sunflower even for 1 day on P. hysterophorus were incapable of ovipositing, and young larvae could not feed on the crop. Under field conditions, newly emerged adults were only attracted to feed on plants that were treated either with a crude aqueous extract of leaves or pollen grains of P. hysterophorus , indicating that the chances of Z. bicolorata becoming a pest of sunflower are negligible. Age-related Feeding by the Parthenium Beetle Zygogramma bicolorata on Sunflower and its EVect on Survival and Reproduction

The introduced Mexican beetle, Zygogramma bicolorata Pallister (Chrysomelidae), has brought about large scale defoliation of the noxious weed Parthenium hysterophorus L. (Asteraceae) in Bangalore and surrounding areas. Studies carried out over a period of two years in two uncultivated parthenium infested horticultural fields showed that defoliation by the beetle can cause up to 99.5% decline in weed density, provided the soil is left undisturbed. Forty different species of plants, formerly suppressed by the weed, were noticed to grow in the areas vacated by parthenium. The studies also indicated that the rate of decline of parthenium and the degree of diversity of succeeding plant species in fallow lands, after defoliation by Z. bicolorata, may vary depending on the duration of weed occupation and the history of land utilisation.

Time-specific life tables were constructed for the Mexican beetle, Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae), which is a promising biological control agent of the Neotropical weed, Parthenium hysterophorus L. (Asteraceae) in and around Bangalore, India. Infertility of eggs (46.00–71.10%) was found to be the key mortality factor, followed by death during the pupal stage (15.76–21.38%), as confirmed by key mortality factor analysis and construction of survivorship curves. No parasitoids or predators were recorded on this insect, while some of the dead pupae/pre-pupae (2.27–17.24%) were found to be infected by Metarhizium anisopliae (Metchnikoff) Sorokin. The high generation trend values (305.88–557.14), give an indication of the biotic potential of this insect, which was found to cause rapid defoliation of the weed under field conditions.

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.

Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae) of Mexican origin, released in Bangalore in 1984, was observed defoliating Parthenium hysterophorus L. (Asteraceae) in 1988, and had dispersed over 50 000 km2 by 1992. The insect appears to have potential in reducing weed density in those parts of India having moderate weather conditions.