Relative humidity impacts development and activity against Aedes aegypti adults by granular formulations of Metarhizium humberi microsclerotia

Optimization of granular formulations of Metarhizium humberi microsclerotia with humectants

“…However, G, as well as the other humectants tested, is metabolized by microorganisms and may favor the development of contaminants on the pellets, thereby potentially impeding the development of the entomopathogen on the pellets. The addition of 10% (w/w) G in the pellets increased their moisture content to a level that, under the tested conditions, permitted MS to develop mycelium and new conidia, even at suboptimal ambient humidity [6]. When tested with 40% G in the formulation, pellets prepared with MC eventually accumulated so much additional water as to hamper fungal development and conidiogenesis on the waterlogged pellets.…”

“…The biomass containing MS was mixed with one of the powdered carriers, the humectant, and distilled water (Table 1) in a stainless-steel container and then manually mixed to homogeneity for 5 min. The mixture was then extruded through a circular plate with 0.5 mm diameter perforations (Caleva 20®; Caleva) adjusted to 25 rpm, and then processed in a spheronizer (Caleva MBS) set at 1500 rpm for 3 min [6]. Pellets were dried at 40 ± 1°C in a fluidized bed dryer (Mycrolab®; Hüttlin) for 30 min.…”

“…Pellets were dried at 40 ± 1°C in a fluidized bed dryer (Mycrolab®; Hüttlin) for 30 min. The water content of pellets was assessed with an infrared moisture balance (IV2000®; Gehaka), and moisture was stabilized at <5% (w/w) [6,13]. Pellets were stored in plastic bags at −20°C, and their viability (>98%) was confirmed before each assay inoculating 30 mg on water-agar medium (2% w/v) and then assessing fungal development for 100 pellets after a 5-day exposure at 25 ± 1°C, >98% RH, and 12 h photophase.…”

“…The RH inside the containers was monitored as mentioned. Containers were kept in a major container (350 × 200 × 350 mm) at 25 ± 1°C and 12 h photophase [6].…”

“…Recently, a granular formulation technique using extrusion and spheronization has been developed to produce pellets with either microcrystalline cellulose or vermiculite, a clay mineral, as carriers [5]. MS incorporated in these pellets were able to produce new conidia at a minimal humidity of 93% [6]. The requirement for high ambient moisture could be an impediment for the use of MS-based formulations in pest control as shown in field tests with Metarhizium brunneum against adults of the Asian longhorned beetle, Anoplophora glabripennis [7,8], and in laboratory tests with Aedes aegypti eggs [9].…”