Insect pathogenic fungi and desiccant dust against heat stressed bed bugs : maternal effects and response regulation from feeding

Abstract

The development of novel control options is a prerequisite for improved management of the insecticide resistant common bed bug Cimex lectularius. This laboratory study investigated the killing ability of insect pathogenic fungi Beauveria bassiana or desiccant dust (syloid) on bed bugs after having been exposed to sub-lethal heat stress at 32°C, 34°C and 36°C for 5 continious days. The first instar nymphs were only indirectly exposed to sub-lethal heat through their parents. Heat stressed adults and their nymphs were exposed to fungi or syloid for 5 minutes or 3 days respectively. Maternal effects from heat stress passed to the next generation and drastically impacted the survival of first instar nymphs without showing any immediate effect on adults. Syloid caused 100% mortality within 3 days for adults or 2 days for nymphs whereas fungi had a slower impact with only 60% mortality after 20 days. The exposure to fungi or syloid appears to override the effect from previous heat stress and no striking synergistic or additive effects were found in susceptibility. Indications of a temperature dependent increase in mortality were observed in most treatments, but this was only significant among the offspring. Access to blood increased survival among the offspring, fungi treated offspring and syloid treated adults compared to starved individuals. The practical use of the result seems limited as no major synergies related to application of fungi or desiccant dust were detected, but it is shown that, heat stress in combination with denial of blood may improve the overall treatment success through reduced performance among adults and their offspring.