Host range and biology of three rice caseworms [Philippines]

On all development parameters, rice was the most nutritious host; 85% larvae pupated and 67% emerged as adults. The polyphagous rice caseworm developed on 23 plant species representing 18 genera and 2 families. Survivorship to adulthood was low (2-36%) on the 22 nonrice hosts. The larval growth index includes two developmental parameters: survival and days to pupation. A high growh index occurs with high survival and short developmental period. More than 20% of adults reared on Leptochloa chinensis, Polytrias amaura, Chrysopogon aciculatus, Leersia hexandra, and Ischaenrum muticum emerged. Neither P. fluctuosalis nor P. diminutalis survived on rice. They are true aquatic caseworms (they remain underwater during their entire larval period). N. depunctalis larvae are semiaquatic, ascending rice plants at night to feed. The most suitable host of P. fluctuosalis on P. diminutalis was the aquatic weed Hydrilla verticillata, which occurs in more permanent bodies of water such as reser1495voirs and canals. Several of the needle-shaped leaves are tied together by the larva to make a case. The rearing method for both aquatic caseworms was less than ideal on Hydrilla; only 40-50% survived to adulthood. They pupate out of water on plant vegetation. The host range of P. diminutalis was three times less than N. depunctalis and overlapped entirely with P. fluctuosalis, which accepted three more plant hosts. All three caseworms shared five host plants, four of them sedges: Fimbristylis miliacea, Cyperus brevifolius, C. difformis, C. rotundus, and Paspalum conjugatum. All these caseworms are similar in size and fertility. P. diminutalis has four larval instars, one less than the P. fluctuosalis and N. depunctalis; matures about 10 d than earlier 2; and has a longer egg incubation period. The sex ratio favored the development of females in P. diminutalis and P. fluctuosalis. Probably because of the lack of a better rearing method. The present rearing method seemed to favor larger individuals, which were mostly fema