Laboratory assessment of the potential of<i>Paranosema locustae</i>to control immature stages of<i>Schistocerca gregaria</i>and<i>Oedaleus senegalensis</i>and vertical transmission of the pathogen in host populations

Abstract

Abstract We tested the effects of Paranosema locustae spores in wheat bran formulation on the immature stages of Schistocerca gregaria and Oedaleus senegalensis under laboratory conditions. Younger instars were the most sensitive to the pathogen. While 100% infection was recorded in younger instar nymphs, older instars were less sensitive, with 16–27% of the inoculated nymphs remaining uninfected at the end of the experiment. Mortality of each instar increased with increased spore concentration. Immature survival time was significantly reduced by the pathogen and none of the nymphs inoculated as first, second, and third instar nymphs developed to adulthood (6–30% and 55–74% of nymphs inoculated as fourth and fifth instar, respectively). Sublethal effects such as delayed host growth, reduced host size, and abnormal wing and leg development (37% of emerging adults) were noted. Almost half the infected adults showed morphological abnormalities at emergence. Moreover, infection in S. gregaria and O. senegalensis by P. locustae did not affect female oviposition. However, 60% of S. gregaria and 52% of O. senegalensis progeny clearly showed infection by P. locustae with infection intensity of 1.08±0.27×101 and 1.19±0.32×102 spores/nymph, respectively. In view of the mortality rates, immature survival, host growth, and abnormal development in the P. locustae treatments, and the high prevalence of the pathogen in offspring from infected parents, it can be expected that the reduction in the impact of the two acridid species in the field will be considerable. Keywords: biological control Oedaleus senegalensis Paranosema locustae Schistocerca gregaria vertical transmission Acknowledgements This research was supported by grants from the International Institute of Tropical Agriculture (IITA) and the German Academic Exchange Service (DAAD) in collaboration with the Leibniz University of Hanover (Germany). Authors are thankful to Prof. C. Borgemeister at ICIPE, Nairobi (Kenya) and Dr. J. Langewald at BASF Agrarzentrum, Limburgerhof (Germany) for their collaboration in this research work. We are grateful to Drs. K. Hell and D. Gnanvossou at IITA Benin station and to Jean N.K. Maniania at ICIPE, Nairobi for their critical review of the manuscript.