Increased tolerance of Beauveria bassiana and Metarhizium anisopliae conidia to high temperature provided by oil-based formulations

Abstract

The influence of the temperature of aqueous conidial sprays on conidial viability and virulence against Diatraea saccharalis was evaluated for pure conidia, rice + fungus (technical concentrates) and oil-based formulations of Beauveria bassiana s.s. and Metarhizium anisopliae s.s. under laboratory conditions. The fungal preparations were suspended in water and maintained at 26 °C, 36 °C and 46 °C for one, four and six hours. Conidial viability was determined by plating aliquots of each suspension onto PDA medium followed by incubation for 20-22 h and observing for viable conidia (germ tubes longer than diameter of conidia). Fungal virulence was determined by spraying suspensions onto third-instar larvae of D. saccharalis. In general, germination and virulence, particularly for unformulated conidia, were negatively affected by increases in water temperature and exposure time in suspension. However, the decrease in conidial viability in the oil-in-water emulsion was less than 7% for both species after 6 h of exposure at 36 °C, in contrast to reductions of 7-21% and 28-60% for the oil-free suspensions of B. bassiana and M. anisopliae, respectively. For the sprays of conidia in an oil-in-water emulsion previously exposed to elevated water temperatures for longer periods, the levels of insect mortality were higher than those of pure conidia or technical concentrates under identical conditions. Our results indicate that emulsifiable oil-based formulations can protect the conidia of both species of fungi from the adverse effects of high water temperatures before spraying in the field.

Endophytic colonization of tomato plants by the entomopathogenic fungus Beauveria bassiana for controlling the South American tomato pinworm, Tuta absoluta

“…However, formulation techniques have been shown to increase EPF viability under stressful environmental field conditions. For example, emulsifiable oilbased formulations increased fungal tolerance to high temperatures (Oliveira et al 2018), whilst addition of vegetable oils to conidial suspensions increased protection against the harmful effects of UV (Kaiser et al 2018).…”

Interactions of fungal entomopathogens with synthetic insecticides for the control of Kuschelorhynchusmacadamiae (Coleoptera: Curculionidae)

“…Without protective formulations, EPF are poorly active against targeted insects under field conditions (Kaiser et al., 2020). Studies have shown that oil‐based formulations can provide protection from unsuitable weather conditions (de Oliveira et al., 2018) and result in a greater impact on insect pests (Kaiser et al., 2020; Luz & Batagin, 2005). In this study, vegetable oil, canola oil (Codacide ® ) and olive oil were able to protect the conidia of both fungal species from solar UV radiation under glasshouse conditions.…”

Isolation, fermentation, and formulation of entomopathogenic fungi virulent against adults of Diaphorina citri

“…Conidia were considered germinated (i.e. viable) if they had a germ tube longer than their diameter after 16 h of incubation at 26 ± 0.5 °C with a 12 h photoperiod 26 . Conidial viability was checked before each experiment and reached 90% of germination in all cases before the formulation experiments unless expressly stated otherwise.…”

“…In contrast to unformulated conidia, oil formulation can elevate the virulence and shelf life of formulated conidia against whitefly 23 and grasshoppers 24 . Different carriers, including mineral oil 25 and soybean oil, 26 are reported for oil‐based formulations. Besides these carriers, sesame oil can resist high temperatures and UV light effects and therefore can be exploited as a sunscreen to minimize the effect of UV in different healthcare products, 27 indicating the potential of sesame oil as a valuable carrier for the formulation of biopesticides.…”