Does Elevated Body Ni Concentration Protect Insects Against Pathogens? A Test Using Melanotrichus boydi (Heteroptera: Miridae)

—I hypothesized that the naturally elevated Ni concentration of Melanotrichus boydi (718–789 mg g21) might protect this insect species against pathogen attack. I contrasted survival of M. boydi against survival of the low-Ni mirid Lygus hesperus when treated with three entomopathogenic biocontrol agents. Biocontrol agents used were the fungus, Beauveria bassiana, and infective juveniles of two nematode species (Steinernema carpocapse and Heterorhabditis bacteriophora). Biocontrol agents suspended in water were sprayed onto insects placed in petri plates in the laboratory. Control treatments consisted of spraying water onto comparable replicates. Separate experiments examined effects of biocontrol agents on nymphs and adults of each species. I monitored insect survival for 4 d after treatment and used survival analysis to contrast survival of individuals receiving control and biocontrol treatments for each species. Biocontrol agents significantly reduced the survival of L. hesperus in all but two trials and reduced the survival of M. boydi in all experimental trials. Both insect species were susceptible to these pathogens and I rejected the hypothesis that elevated body Ni concentration protects M. boydi from pathogen attack.