Host preference and potency of Altica cyanea as a bio-control agent of major rice field weeds, Ludwigia spp.
The water primrose, Ludwigia spp. (L. adscendens, L. prostate, L. hyssopifolia) (Onagraceae) are wide spread decumbent weeds commonly found in rice field and wetland ecosystem abundantly throughout India and elsewhere. They are highly invasive and commonest form of weed species in the Indian rice field ecosystems including West Bengal. They induce nutrient partitioning with the rice plants and thus reduce their production along with short and long term allelopathy on the other subsequent economic crops cultivated after rice. Usually, herbivores are used as bio-control agent to regulate weeds without interfering the cropping system. It is well known that chemical signals and nutritional constituents play an important role in the interactions between plants and phytophagous insects. The weeds attract the flae beetle, Altica cyanea Weber (Coleoptera: Chrysomelidae) for defoliation by means of chemical signals. The life history and host-preference of the flea beetles were studied to determine its potential value as a biological control agent for one of the major rice field weed, L. adscendens over the other two species of Ludwigia. The phytochemical constituents including nutritional and some anti-nutritional factors were correlated with such type of preference and survivability of this bio-control agent. Thus the study support the potency of the flae beetle, A. cyanea, as a bio-control agent of the major rice field weed, L. adscendens over the other two Ludwigia spp. (L. prostate, L. hyssopifolia) and they can be used for better production of rice as well as other subsequent crops cultivated after rice.