Studies on the insect fauna and other invertebrates associated with Azolla spp.
The invertebrates present on Azolla spp., an aquatic fern which is used as green manure, were surveyed in the Philippines in 1985. Population fluctuations of the pyralid Ephestiopsis vishnu were studied in the field in January-June 1985 and the resistance of Azolla species and strains to this species and to 2 other pyralids, Nymphula enixalis and N. responsalis, was evaluated. Six pest species, E. vishnu, N. enixalis, N. responsalis, Polypedilum johannseni, Polypedilum sp. and Rhopalosiphum nymphaeae, were recorded. Several predatory species were also collected. Populations of E. vishnu peaked at different times on different strains of A. pinnata, A. mexicana, A. filiculoides and A. microphylla. Based on larval counts, strains of A. microphylla, except for 305, were the most preferred by the pyralids, while A. pinnata 704 was the least preferred. It is suggested that insect pests may prevent Azolla species from becoming weeds in lowland rice.