Desiccation risk of biological control agent pupae in a mass release strategy

Authors: Halbritter, Dale; Wheeler, Gregory; Rayamajhi, Min

Submitted to: Entomological Society of America Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 11/17/2019
Publication Date: N/A
Citation: N/A

Interpretive Summary: Insects are especially susceptible to drying out because of their small size. Hiding in damp areas , undergoing dormancy , having a water-resistant coating, or absorbing moisture from the air are among some of the ways insects can prevent or recover from water loss. The thrips Pseudophilothrips ichini is a promising biological control agent of Brazilian peppertree and thrips larvae pupate on the soil’s surface among leaf litter. We investigated the utility of using clumps of sphagnum moss to move thrips pupae into wildlands infested with Brazilian peppertree. Specifically, we tested the impact of humidity on thrips survival in dry moss during their 1- to 2-wk pupation window. Pupae-laden moss clumps were either exposed to very humid (~100% relative humidity), dry (~50% relative humidity), or fluctuating every 48 h between dry and very humid air. The fluctuating humidity mimics what could happen during a rain-free period in the field in which humidity periodically recovers, especially at night, allowing the pupae to potentially re-hydrate. The implications of these thrips moss “bombs” for a mass release strategy will be discussed.

Technical Abstract: Insects face the challenge of desiccation due to their small size and high surface area to volume ratios. Seeking favorable microclimates, undergoing dormancy or quiescence, having a waxy cuticle, or the uptake of atmospheric water are among some of the adaptations insects have acquired to prevent or recover from water loss. The thrips Pseudophilothrips ichini (Thysanoptera: Phlaeothripidae) is a promising biological control agent of Brazilian peppertree whose larvae pupate on the soil’s surface among organic litter. We investigated the efficacy of using clumps of sphagnum moss as vehicles to establish thrips populations in wildlands infested with Brazilian peppertree. Specifically, we tested the impact of ambient humidity on thrips survival in dry moss during their 1- to 2-wk pupation window. Pupae-laden moss clumps were either exposed to atmospheres consistently near saturation (~100% RH), dry (~50% RH), or fluctuating between dry and saturated every 48 h. The fluctuating humidity models what could happen during a rain-free period in the field in which humidity periodically recovers, especially at night, allowing the pupae to potentially re-hydrate. The implications of these thrips “bombs” for a mass release strategy will be discussed.