Experimental studies to evaluate spray applications of a mycoinsecticide against the rice grasshopper, Hieroglyphus daganensis, in northern Benin

Abstract

Three experiments were conducted to examine the effects of spray applications of a mycoinsecticide against the rice grasshopper, Hieroglyphus daganensis, in northern Benin. The experiments were designed to expand on previous evaluation studies and contribute to a better understanding of the overall impacts of mycoinsecticide applications. The first experiment showed that acquisition of spores from the spray residue had a significant effect on mortality rate and a greater single influence on mortality than direct contact with spores from the spray aerosol. The second and third experiments revealed the mycoinsecticide to have sub‐ and pre‐lethal effects, causing a significant reduction in per capita feeding rate and increasing susceptibility to predation. The significance of these results for the overall impact of spray applications and for development of comprehensive evaluation methods are discussed.

Ecological approaches and the development of “truly integrated” pest management

“…For example, studies have revealed that infected hosts appear to be more vulnerable to predation than healthy hosts before death (ref. 19 and unpublished data). This phenomenon may have benefits in that speed of kill after application may effectively be increased through the pathogen's interaction with other mortality factors, although the extent to which this mortality occurs will depend on the nature and abundance of natural enemies at the site of application.…”

“…This result has been shown in laboratory and field settings for a range of species and pathogen doses (19)(20)(21)(22). Thus it appears that the overall impact of the biopesticide is determined by more than just mortality rate (which can be slow under field conditions; see below) and that even infections with very low levels of pathogen still may have important consequences for control.…”

The Role of Viral Infection in Pest Control: A Mathematical Study

“…For example, studies have revealed that infected hosts appear to be more vulnerable to predation than healthy hosts before death (Thomas et al, 1998). This phenomenon may have additional benefits in that speed of killing or mortality of pests, although the extent to which this mortality occurs will depend on the nature and abundance of natural enemies at the site of application.…”

“…The viral infection makes some behavioral changes and sublethal effects on host. It impairs the pest defense by reducing their stamina, creating disorientation and altering their responses, which make them more vulnerable to predation by natural enemy than healthy hosts (Thomas et al, 1998). There are many examples of parasites modifying the behavior of the infected individuals in the host population (Holmes and Bethel, 1972;Lafferty and Morris, 1996).…”

“…The natural enemy or predator P consumes both the susceptible and infected pests with the fact that the infected pests are more vulnerable to predation due to the disease (Thomas et al, 1998) and due to the same reason also the handling time for infected pest is, in fact, negligible. So, assuming a 0 is the rate of searching multiplied by the probability of finding a susceptible, the predation rates for susceptible and infected are of the forms,…”