Assessing heat tolerance of distinct agent populations to predict biological control performance

Authors: FOSTER, BRIANNA - University Of Florida; Leidi, Jorge; Dray Jr, Forrest; Halbritter, Dale

Submitted to: International Symposium on Biological Control of Weeds
Publication Type: Abstract Only
Publication Acceptance Date: 3/10/2026
Publication Date: 3/10/2026
Citation: Foster, B.M., Leidi, J.G., Dray Jr, F.A., Halbritter, D.A. 2026. Assessing heat tolerance of distinct agent populations to predict biological control performance. International Symposium on Biological Control of Weeds, March 8-13, 2026, Rotorua, New Zealand.

Interpretive Summary: The thrips Pseudophilothrips ichini was released in Florida in 2019 to help control the invasive Brazilian peppertree. Although the insect has been established at some sites, its numbers often drop during the hot summer months, raising concerns that high temperatures may limit its effectiveness. Temperature stress is especially important in insects like thrips, where unfavorable conditions can change the balance of males and females, potentially reducing population growth. To explore this, we compared three populations of P. ichini: the established population from Minas Gerias, a population from Bahia still in quarantine, and hybrids created by crossing the two. Each group was tested at standard laboratory temperatures and at higher summer-like temperatures. We measured the number of offspring produced, sex ratios, body size, and plant damage. This study will help determine whether the Bahia population or hybrids might perform better under Florida’s summer conditions.

Technical Abstract: The biological control agent Pseudophilothrips ichini (Hood) (Thysanoptera: Phlaeothripidae), native to Brasil, has been released in Florida since 2019 to manage the invasive shrub Brazilian peppertree (Schinus terebinthifolia Raddi). While P. ichini has successfully established at several sites, populations often decline during the summer months, suggesting that high temperatures may hinder persistence. Such maladaptation can be particularly consequential in haplodiploid insects, where unfavorable conditions may skew sex ratios, limiting long-term field efficacy. To assess thermal and population level responses, we compared three P. ichini populations with distinct genetic backgrounds: (1) the Minas Gerais population, currently established; (2) the Bahia population (in quarantine since 2022); and (3) hybrids produced through crosses of Minas Gerais and Bahia individuals. Each population was reared under two environmental chamber conditions: a high summer-relevant temperature (24-32 °C daily oscillations) and a standard laboratory temperature (24 °C). We measured performance based on offspring production, sex ratio, morphological metrics, and damage to the target plant. This design allowed us to test whether geographic origin of a population influences heat tolerance and whether hybridization alters performance either generally or in response to temperature. Our findings will clarify whether alternative populations or hybrids offer advantages under Florida summer conditions.