First detection of a microsporidium in the crucifer pest Hellula undalis (Lepidoptera: Pyralidae)—a possible control agent?

For the first time, a microsporidian infection was observed in the pest species Hellula undalis (Lepidoptera: Pyralidae) in crucifer fields in Nueva–Ecija, Philippines. Because H. undalis is difficult to control by chemical insecticides and microbiological control techniques have not been established, we investigated the biology, the pathogenicity and transmission of this pathogen found in H. undalis. An average of 16% of larvae obtained from crucifer fields in Nueva–Ecija displayed microsporidian infections and 75% of infected H. undalis died during larval development. Histopathological studies revealed that the infection is initiated in the midgut and then spreads to all organs. The microsporidium has two different sporulation sequences: a disporoblastic development producing binucleate free mature spores and an octosporoblastic development forming eight uninucleate spores. These two discrete life cycles imply its taxonomic assignment to the genus Vairimorpha. The size of the binucleate, diplokaryotic spores as measured on Giemsa-stained smears was 3.56±0.29 μm in length and 2.18±0.21 μm in width, whereas the uninucleate octospores measured 2.44±0.20×1.64±0.14 μm. The microsporidium was orally and probably also transovarially transmitted. Laboratory infection tests by feeding spores on artificial diet to 3rd instars resulted in 100% infection with a final mortality of 80%. Most larvae died during larval development and 40% of them died 3 days after spore ingestion. This microsporidium shows potential for microbiological pest management.