Formulation of Metarhizium anisopliae (Metschnikoff) Sorokin with biodegradable polymers and their virulence against Heliothis virescens (Fabricius)

Propagules of Metarhizium anisopliae (Metchnikoff) Sorokin were obtained from solid fermentation of rice grains to produce microcapsules by the spray drying technique. Bovine gelatin, nixtamalized corn, and corn starch were used as matrix, in addition to a feeding stimulant and a UV protector. Eight microencapsulated formulations were obtained adjusting the spray drying conditions to 120 ºC and 70 ºC of inlet and outlet temperatures, respectively, and to a flow rate of 3.34 mL/min. Previously, feeding preference tests with Heliothis virescens (Fabricius) were conducted with two feeding stimulants (chickpea and vegetable oil). To select the formulation with the highest adherence capacity, adhesion trials were performed with five water washes (64 mL/min during 24 s) on glass slides. The virulence of these formulations was assessed through a bioassay using first instar H. virescens larvae. Mortality was recorded after seven days. The selected formulation (F6) showed the highest adherence to slide (85.55 ± 1.79 [%]), highest larvae feeding preference (6.6 ± 1.24 [%]), and contained bovine gelatin (26 g), corn oil (20 mL), red dye (4 g) and M. anisopliae (1x109 spores/g). The results showed that the drying process of the fungus produced encapsulating granules with particle size < 20 µm, moisture content of 8.74 ± 3.6 [%], spore germination values of 5.4 ± 0.6 [%] (after 24 h), and fungi virulence of 10.31 [%] tested on first instar H. virescens larvae. Since virulence was low, decreasing dryer´s inlet temperature (between 60 ºC and 70 ºC) may increase the spore survival as well as the effectivity of the formulation on larval mortality.