Tritrophic interactions between a fungal pathogen, a spider predator, and the blacklegged tick

Abstract

The blacklegged tick Ixodes scapularis is the primary vector for the bacterium causingLyme disease in eastern North America and for other medically important pathogens.This species is vulnerable to attack by fungal pathogens and arthropod predators, butthe impacts of interactions between biocontrol agents have not been examined. Thebiocontrol agent Met52®, containing the entomopathogenic fungus Metarhiziumbrunneum (=M. anisopliae), controls blacklegged ticks with efficacy comparable tochemical acaricides. The brush-legged wolf spider Schizocosa ocreata is a predator ofI. scapularis that reduces their survival under field conditions. We conducted a fieldmicrocosm experiment to assess the compatibility of Met52 and S. ocreata as tickbiocontrol agents. We compared the fits of alternative models in predicting survivalof unfed (flat) and blood-fed (engorged) nymphs. We found the strongest support fora model that included negative effects of Met52 and S. ocreata on flat nymph survival.We found evidence for interference between biocontrol agents, with Met52 reducingspider survival, but we did not find a significant interaction effect between the twoagents on nymph survival. For engorged nymphs, low recovery rates resulted in lowstatistical power to detect possible effects of biocontrol agents. We found thatnymph questing activity was lower when the spider was active above the leaf litterthan when the spider was unobserved. This provides the first evidence that predationcues might affect behavior important for tick fitness and pathogen transmission. Thisstudy presents field microcosm evidence that the biopesticide Met52 and spiderSchizocosa ocreata each reduced survival of blacklegged ticks Ixodes scapularis. Met52reduced spider survival. Potential interference between Met52 and the spider shouldbe examined at larger scales, where overlap patterns may differ. Ticks were morelikely to quest when the spider was inactive, suggesting the ticks changed theirbehavior to reduce danger.