Entomopathogenicity of Vairimorpha sp (Microsporidia) in the diamondback moth, Plutella xylostella (Lepidoptera: Yponomeutidae)

The biocontrol potential of a microsporidian pathogen, Vairimorpha sp., obtained from field collected diamondback moth, Plutella xylostella Linnaeus, was assessed in a laboratory colony of this insect. The pathogenicity was quantified using a standard bioassay procedure by infecting second instar larvae per os with variable dose levels of the pathogen. Vairimorpha sp. caused 100% mortality even at a dosage of 1.5 x 10(3) spores per larva. The median lethal dose (LD50) was 2.2 x 10(4) spores per larva on day 5 post-inoculation. The time taken to achieve 90-100% mortality was dose dependent and varied from 5 days with 1.5 X 10(6) spores per larva to 11 days with 1.5 X 10(3) spores per larva. The pathogen reduced the food consumption of P. xylostella larvae by 75%, 93% and 95% at doses 1.5 x 10(4), 1.5 x 10(5) and 1.5 x 10(6) spores per larva, respectively. Histological observations showed that the pathogen preferentially infected adipose tissue cells but spread to almost all tissues. The pathogen was transmitted transovarially as well as horizontally and had a marked influence on progeny performance. It was concluded that Vairimorpha sp. has sufficient potential to be tested in the field as a biocontrol agent for P. xylostella.