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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.

Observations under field conditions in Bangalore showed that release of Neochetina eichhorniae and N. bruchi (Coleoptera: Curculionidae) brought about successful control of the water hyacinth in water bodies where the plants were free-floating. However, in situations where the plants were partly anchored, suppression of the weed was achieved only 8 years after insect release. Studies carried out under glasshouse conditions, in which plants with free-floating and silt-covered roots were exposed to Neochetina spp., showed that fully grown larvae were incapable of pupating on silted roots of the water hyacinth. This resulted in reduced adult emergence of N. eichhorniae and N. bruchi, indicating that delayed suppression of water hyacinth in silted tanks may be due to the low population build-up of the weevils.

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 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.

Bactra venosana Zeller (Lepidoptera: Tortricidae) is the predominant natural enemy ofCyperus rotundas L. in Bangalore, India. Although the insect was found to have potential, it was incapable of suppressing the weed due to low incidence. Laboratory studies involving field-collected insect stages revealed that heavy parasitism of eggs byTrichogrammatoidea bactrae Nagaraja (Hymenoptera: Trichogrammatidae) was the most important mortality factor suppressing its potentiality.

Bessa remota (Ald.) was introduced from Malaysia for trials againstOpisina arenosella Wlk., an important pest coconut in India. Its development was studied onO. arenosella reared on artificial diet. Eggs were laid readily on half to full grown larvae and incubation, larval and pupal periods were 2.18, 6.69 and 9.34 days respectively at 25°±2°C, 60–80% R.H. Females lived for 23 days producing 108.29 eggs, of which 53.10% yielded puparia. Among 8 other lepidopterous hosts tested 4% to 20% parasitism was observed onCrocidolomia binotalis (Z.),Spodoptera litura (Fb.),Sylepta derogata Fb. andTrichoplusia ni Hb.

The aquatic fernSalvinia molesta D.S. Mitchell is a serious weed in India, espacially in the state of Kerala. The weevilCyrtobagous salviniae Calder and Sands (Col.: Curculionidae) was introduced from Austrialia and successfully controlled the weed infesting a lily pond at Bangalore.