Effect of Paranosema (Nosema) locustae (Microsporidia) on morphological phase transformation of Locusta migratoria manilensis (Orthoptera: Acrididae)

Abstract

Field and laboratory studies demonstrated that Paranosema (Nosema) locustae had significant effects on the morphological phase transformation of Locusta migratoria manilensis (Meyen 1835). In the field, spraying P. locustae on gregarious locusts caused a substantial population reduction by 16 days after treatment, with most of the surviving locusts being phase solitaria. However, the effects of P. locustae on locust phase transformation began before direct mortality had caused a substantial reduction in locust density: locust numbers were still high at day 10, but locusts had already transformed to phase transiens. Laboratory assays showed that while a low dose of P. locustae had no effect on phase transformation, at a higher dose of 1×10⁵ spores/mL, locusts had F/C ratios that were significantly (P<0.05) more solitaria than untreated locusts, with locusts having ratios that were either phase solitaria or on the solitaria side of phase transiens. In a second laboratory experiment that analysed the effects of locust density on phase transformation by P. locustae, there was no obvious effect of density on female locusts 10 days later as all were solitaria at all locust densities. At day 16, female locusts were transiens at higher densities, but were solitaria at 4/cage. With males there were lesser effects. These results provide new evidence for P. locustae having sub-lethal effects on locust phase transformation at a wide range of locust densities.

Keywords:

• Locusta migratoria manilensis
• Paranosema (Nosema) locustae
• morphological phase

Acknowledgements

Thanks to Dr Long Zhang and Mr Honghai Li in the Department of Entomology, China Agricultural University and Mr Zhigeng Xie in the Dagang County Locust Station for their help during the experiments in the field. The Beijing Science Foundation (Z09050200890905) and the National Key Technologies Research and Development Program of China funded this research during the 11th Five-Year Plan Period (2008BADA5B05, 2008BAD92B08 and 2008ZX08011).