Interactions of monocrotophos and quinalphos with Anabaena torulosa isolated from rice soil

The interaction of insecticide combinations of monocrotophos and quinalphos on Anabaena torulosa, by the criteria of absorbance (OD) and packed cell volume (PCV) of the culture, content of chlorophyll a, phycocyanin, carotenoids, total protein, DNA and RNA, heterocyst differentiation and nitrogen fixation, were assessed. In general, monocrotophos and quinalphos, in combination, interacted significantly yielding three different responses viz., additive, antagonistic or synergistic. The nature of the interaction found with OD and PCV was nearly the same for a particular concentration of the insecticides. However, no consistent interaction was observed with respect to carotenoids and phycocyanin. The three types of interaction were noticed for total protein, DNA and RNA. Interestingly, the insecticide combinations at lower concentrations yielded all interaction responses for heterocyst frequency and nitrogenase activity. But, higher concentrations, in combination, resulted in synergism for heterocyst differentiation and nitrogen fixation.