Hirsutella citriformis Speare is the only entomopathogenic fungus that has been applied to control the hemipteran Diaphorina citri Kuwayama. However, the use of available commercial products under field conditions is limited due to conidia’s shelf life and short environmental persistence. We have previously reported the citrus psyllid D. citri adults’ biocontrol potential using H. citriformis strains. The aim of the present study was to evaluate different formulations based on H. citriformis (OP-Hir-3, OP-Hir-10, and OP-Hir-12 strains) conidia and gums as additives to improve D. citri adults’ biocontrol, under laboratory, greenhouse, and field conditions, using Hirsutella gums as conidia stabilizers to improve their viability under environmental drought conditions and as insecticide. Laboratory bioassay results showed that the highest (p < 0.05) D. citri mortality was achieved using FOP-Hir-10GH (63.5%), followed by the Hirsutella gum control (42.2%). Under greenhouse conditions, adults’ mortality reached up to 84.6% with FOP-Hir-12 and 49.0% with Hirsutella gum. In addition, we applied H. citriformis formulations under field conditions in a commercial citrus grove located in Tecomán, Colima, México, at 21.5 °C and 73.3% relative humidity (RH) in March and 25.7 °C and 72.5% RH in October 2022 and observed 67.3% and 94.0% mortality of D. citri adults, respectively. Hirsutella gum alone showed significant insecticidal activity against D. citri adults. In conclusion, this study demonstrated that Hirsutella gum functioned as additive to H. citriformis conidia formulations, improving D. citri adults’ mortality and showing potential for this pest biocontrol in citrus orchards.

Biological control by beneficial microorganisms is known to significantly reduce the effect of pests on crops yield. Among the biocontrol strategies is the use of entomopathogenic fungi such as Hirsutella citriformis, which has been applied to infect and kill hemipteran insect pests, including Diaphorina citri Kuwayama (Hemiptera: Liviidae) and Bactericera cockerelli Sulc. (Hemiptera: Triozidae). These biological agents are applied in the form of conidia that are often combined with other inert materials to facilitate application, protect conidia, and improve their shelf life. The aim of this study was to implement strategies for developing formulations to increase conidia shelf life. We evaluated gum produced from one strain and conidia from two different H. citriformis strains. Conidia were formulated by evaluating different concentrations of Acacia and Hirsutella gums to enhance conidia viability during storage at 4 °C or 25 °C. Results indicated that formulations maintained conidia viability for at least 90 d after storage at 25 °C (≥70% viability) and at least 120 d after storage at 4 °C, which was significantly (p ≤ 0.05) higher than that of the control, without observing changes in pH values. We also demonstrated 100% formulation purity from days 0 to 120, among all treatments. In conclusion, evaluated formulations maintained H. citriformis conidia viability for at least three months, when stored at 4 °C.

Desert ecosystems harbor microbial communities adapted to extreme environmental conditions, including water scarcity, elevated temperatures, and intense UV radiation. Among these microorganisms, microalgae represent promising resources for agricultural applications. In this study, microalgae isolated from desert soils in Mexico were characterized by molecular (rbcL) and phylogenetic analysis, and morphological observations. They were identified as Chlorella sp. (RAD3), Nannochloris-related isolate (RAD4), and Chlorella cf. variabilis (RAD5). The effects of microalgal biomass on maize (Zea mays L.) germination and early seedling development were evaluated using a seed-priming approach. Microalgal treatments significantly improved (p < 0.05) germination-related traits, seedling vigor, shoot height, root length, and fresh and dry biomass, as compared with the control. Chlorella cf. variabilis (RAD5) was associated with reduced germination time, whereas Nannochloris-related isolate (RAD4) consistently produced the strongest responses in vigor and growth parameters. Although some variables reached their highest numerical values at 10⁸ cells/mL, similar responses were usually observed at 10⁷ cells/mL. Overall, the evaluated desert-derived microalgal preparations were associated with improved early maize seedling performance, under the evaluated conditions.