| dc.description.abstract | Phosphine (PH₃) resistance and tolerance contribute to the increased importance of psocids (Psocodea: Liposcelididae) as stored-product pests worldwide. However, there is currently no superior substitute for this fumigant to meet domestic and international export phytosanitary requirements in the United States. These studies were conducted in the context of developing PH₃ resistance monitoring strategies to manage resistance in psocids and assessing predatory behaviors of Cheyletus eruditus (Schrank) and Cheyletus malaccensis Oudemans (Trombidiformes: Cheyletidae) to measure their potential as effective biocontrol candidates for psocid management. The first objective was to establish the levels of PH tolerance in laboratory susceptible strains of psocids using a modified FAO Method No.16. To accomplish this, discriminating doses (DDs) were established for lab-cultured susceptible adults of Liposcelis bostrychophila (Badonnel), L. entomophila (Enderlein), L. decolor (Pearman), L. paeta Pearman, L. rufa Broadhead, L. obscura Broadhead, L. fusciceps Badonnel, and Lepinotus reticulatus Enderlein (Psocodea: Liposcelididae) over a 20-h and 72-h fumigation period. The established DDs showed a range of 65.6–697.3 ppm and 18.1–194.5 ppm over 20-h and 72-h fumigation periods, respectively. The higher heterogeneity levels found in the standard 20-h fumigation period indicates the potential for a significant increase in PH₃ resistance in field populations subjected to PH₃ fumigation. The second and third objectives were to assess the predatory efficiency of C. eruditus and C. malaccensis based on their foraging behaviors —functional and numerical responses of these predators to different developmental stages of L. decolor. Both predatory mites showed Holling Type II functional response to nymphs, adult males, or adult females of L. decolor. The estimated functional response variables showed that C. eruditus performance was preferable to C. malaccensis. However, numerical response parameters of predators indicated that C. malaccensis was more efficient than C. eruditus. The fourth objective was to provide quantitative data based on the ecological interactions of C. eruditus or C. malaccensis and L. decolor under different release ratios (predator-prey ratios), temperatures (°C), and relative humidities (RH %) over a 40-d period to determine the optimal psocids management conditions for each predatory mite. The results showed that low RH (≤63%) undermine the efficacy of both predatory mites, however, C. eruditus and C. malaccensis caused psocid population suppression of ~ 67.1–97.2% and increased their progeny by ~ 117.1–1182.6% for the 1:20–10:20 release ratios, temperatures of 20–32°C, and 75–85% RH. Future research should be aimed at using the established DDs for the detection of PH₃ resistance and estimation of resistance frequencies in field-collected populations of the psocid species investigated. Also, field evaluation of both predatory mites and their compatibility with other stored-product pest management tactics are needed to permit release for psocid management in the United States. | |
