First record of Fusarium verticillioides (Ascomycota: Hypocreales) as an entomopathogenic fungus of grasshoppers (Orthoptera: Acridoidea)

PELIZZA S.A., STENGLEIN S.A., CABELLO M. N., DINOLFO M.I. & LANGE C.E.

Carlos paz, Córdoba

Congreso; VI Congreso Argentino de Microbiología General; 2009

The genus Fusarium comprises a large group of species of filamentous fungi widely distributed in soil. More than 13 Fusarium species are pathogenic to insects. Fusarium verticillioides (Sacc.) Nirenberg is often the most common fungus reported from infected corn kernels and vegetative tissues, but has not been recorded as an entomopathogen. Grasshoppers and locusts are important agricultural pests in different parts of Argentina. Tropidacris collaris (Stoll) has become in recent years an increasingly recurrent and extended pest in some of the Northern provinces. Although adults tend to prefer hard-leaf trees and bushes, T. collaris is actually a polyphagous species, and the nymphs bands consume virtually all available plant material they find. Currently, chemical insecticides are the only mean of control. Here we report the detection, by morphological and molecular methods, of an isolate of F. verticillioides in T. collaris, and its pathogenecity in the laboratory against another harmful grasshopper, the Melanoplinae Ronderosia bergi (Stal). During February-March 2008-09, nymphs and adults of T. collaris were collected in western Chaco Province, Argentina. The samples were immediately taken to the laboratory where grasshoppers were kept in groups in wire-screened cages in a rearing room under controlled conditions (30 ºC, 14L: 10D, 60% RH). Grasshoppers that died within 10 days post-collection were surface sterilized and held in a sterile culture chamber consisting of a Petri dish with a filter-paper disk that was periodically moistened with distilled water and incubated at 25 ºC in the dark. The filamentous fungi emerging from dead individuals were transferred to Petri dishes containing PGA + antibiotics, and incubated 26ºC. The fungal species isolated from T. collaris were identified on the basis of the macromorphological appearance of the colonies and molecular techniques were performed to confirm the fungal species. Unfortunately, our efforts to develop a breeding colony of T. collaris were not successful, hence the insects used in this study for testing pathogenicity were Ronderosia bergi, which are bred in the colony at CEPAVE. Three replicates (on different dates) of fifty third-instar nymphs each of healthy R. bergi were sprayed in groups of 10 with 1000 µl of a conidial suspension of 2.8 x 106conidia/ml. Three additional replicates of 20 grasshoppers each were used as controls. Mortality caused by F. verticillioides on R. bergi reached 58 ± 6.53 % by 10 days after inoculation, mortality did not occur among controls. In conclusion, this is the first report of infection of an insect by F. verticillioides and was confirmed by laboratory screening.