Effect of herbicides on feeding, survival and development of Haltica cyanea, a biocontrol agent of dicot weed, Ammania baccifera L. in rice ecosystem

Abstract

Ammania baccifera L. (Fam: Lathyraceae) is one of the predominant weeds in paddy fields. In nature, the adults and grubs of Haltica cyanea (Coleoptera: Chrysomelidae) feed varaciously on the leaves of this weed leading to drying of the plants. In recent times with the gradual change in cultivation practices and increase in labour shortage the use of weedicides in rice ecosystem has increased tremendously. In an endeavour to explore the possibility of the use of these beetles as biocontrol agents, laboratory studies were carried out at ICAR-IIRR to compare the efficacy of H. cyanea as a biocontrol agent in comparison with the two recommended herbicides and also study the effect of these herbicides on the biology of the beetle. The two recommended herbicides, 2,4-D Na salt 80% (for broadleaved weeds) @800g a.i/ha and Metsulfuron methyl 10% + chlorimuron ethyl 10% WP (for broadleaved and sedges) @4ga.i/ha were tested against A. baccifera and the larval stages of H. cyanea. The effect of these herbicides on survival, feeding, longevity and biology of the bioagent was studied through leaf dip and pot spray method. It was observed that there was 21.67% reduction in shoot weight in beetle released plants as compared to herbicide treatment wherein 38.5-49.3% reduction in shoot weight was observed within 48h. Both the herbicides affected the biology of the insect and between the two herbicides, 2,4-D Na salt was more toxic to the grubs as compared to Metsulfuron methyl + chlorimuron ethyl.