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Optimization of granular formulations of Metarhizium humberi microsclerotia with humectants
Alaine M L Catão1, Juscelino Rodrigues1, Ricardo N Marreto2
1Laboratório de Patologia de Invertebrados (LPI), Instituto de Patologia Tropical e Saúde Pública (IPTSP), Universidade Federal de Goiás (UFG), Goiânia, Goiás, Brazil.
Abstract:
Granular microsclerotial formulations of entomopathogenic fungi deserve attention because of their post-application, in situ production of new conidia that enhance and prolong mycoinsecticidal efficacy against a target pest insect. Because high ambient moisture is a crucial condition to induce fungal development and conidiogenesis on granules, we tested the impacts of the additions of three humectants-glycerin, propylene glycol, and polyethylene glycol 400-on water absorption by pellets incorporating microsclerotia of Metarhizium humberi IP 46 with microcrystalline cellulose or vermiculite carriers, and on the production of infective conidia of IP 46 microsclerotia in ambient humidities suboptimal for routine conidiogenesis. Glycerin facilitated greater and faster absorption of water than the other humectants. Microcrystalline cellulose absorbed low quantities of water without any added humectant whereas vermiculite did not. IP 46 did not grow or sporulate on pellets prepared with or without glycerin at 86% relative humidity (RH) or on control pellets without glycerin at 91% RH; conidial production on pellets prepared with vermiculite or microcrystalline cellulose and 10% glycerin reached 1.1 × 105 conidia/mg and 1 × 105 conidia/mg, respectively, after 20 days of exposure at 91% RH. Hence, these results strongly support glycerin as a suitable humectant for granular microsclerotial formulations of this fungus.
Insights
Glycerin enhances water absorption in granular fungal formulations, improving conidia production for insect control. This humectant boosts the efficacy of entomopathogenic fungi like Metarhizium humberi IP 46.
Area of Science:
- Agricultural Science
- Mycology
- Entomology
Background:
- Granular microsclerotial formulations of entomopathogenic fungi offer prolonged mycoinsecticidal efficacy through in situ conidia production.
- High ambient moisture is essential for fungal development and conidiogenesis on granules, which can be a limiting factor in suboptimal conditions.
Purpose of the Study:
- To evaluate the impact of humectants (glycerin, propylene glycol, polyethylene glycol 400) on water absorption and conidia production of Metarhizium humberi IP 46 microsclerotia in granular formulations.
- To determine the effectiveness of humectants under humidities suboptimal for conidiogenesis.
Main Methods:
- Microsclerotia of Metarhizium humberi IP 46 were incorporated into granular formulations using microcrystalline cellulose or vermiculite carriers.
- Different humectants were added to the formulations, and their effect on water absorption was measured.
- Conidia production was assessed after exposing the formulations to specific relative humidity levels (86% and 91% RH) over 20 days.
Main Results:
- Glycerin significantly enhanced water absorption by the granular formulations compared to other humectants.
- Microcrystalline cellulose showed some water absorption without humectants, while vermiculite did not.
- Conidial production reached 1.1 × 10^5 conidia/mg (vermiculite carrier) and 1 × 10^5 conidia/mg (microcrystalline cellulose carrier) with 10% glycerin at 91% RH.
Conclusions:
- Glycerin is a highly effective humectant for improving water retention in granular Metarhizium humberi formulations.
- The addition of glycerin facilitates significant conidia production even in humidities suboptimal for fungal sporulation.
- Glycerin shows strong potential for enhancing the performance of granular entomopathogenic fungal formulations for pest insect control.
