Relation between enzimatic activity and virulence of Metarhizium anisopliae over llanera locust (Orthoptera: Acrididae)

Abstract

Llanera locust, Rhammatocerus schistocercoides (Rehn), represents a serious threat for agriculture and livestock in the Eastern savannas of Colombia. A native isolate of the entomopathogenic fungí Metarhizium anisopliae, grown in rice and formulated, has been successfully used for locust control under field conditions. The effect of the culture medium over fungí virulence has been reported in the scientific literature. The objective of the present work was to evaluate the effect of some potential virulence inductors over the ogical and enzymatic activity of the M. anisopliae conidia. For thís purpose, the isolate Mt004 previously selected by its high virulence against R. schistocercoides and the isolate Mt006 of M. anisopliae which presented the lowest biocontrol activity were grown in a shaken liquid medium and in solid medium containing different potential virulence inductors (colloidal chitin, locust wings and legs, wheat bran. Rhizoctonia solani dead mycelia and Aspergillus niger dead mycelia). Conidia produced in presence of virulence inductors were evaluated under laboratory conditions, against adult locust. The maximum mortality in locust was caused when the fungí was grown in liquid medium supplemented with a homogenized powder of locust wings and legs, this strain presented a lethal time 50 (LT50) of 11 days and 70% of total mortality, 15 days after treatment. Otherwise, Mt004 isolate presented the highest biocontrol activity when the fungi were grown in liquid medium supplemented with both homogenized powder of locust wings and legs and wheat bran. This strain presented a LT50 of 5,8 days and 7,2 days respectively and total mortality of 100% and 100% respectively, 13 and 14 days after treatment. This result suggests that these substrates have a virulence induction effect. Enzymatic activity was higher when the culture was made in the id medium than solid medium and when it was supplemented with homogenized powder of locust wings and legs and wheat bran. The biological activity presented a direct relation with the protease activity of PRl. The found results let conclude that this enzyme is directly related to fungus virulence.