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ARS Home » Northeast Area » Ithaca, New York » Robert W. Holley Center for Agriculture & Health » Emerging Pests and Pathogens Research » Research » Publications at this Location » Publication #302789

Title: Seasonal prevalence of the insect pathogenic fungus Colletotrichum nymphaeae in Brazilian citrus groves under different chemical pesticide regimes

item MASCARIN, G. - Universidade De Sao Paulo
item MOLINA GUARIN, J. - Corpoica
item PAULI, G. - Universidad De Sao Paulo
item Humber, Richard
item DELALIBERA, JR., I. - Universidad De Sao Paulo

Submitted to: Fungal Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2015
Publication Date: 5/31/2016
Citation: Mascarin, G.M., Molina Guarin, J.H., Pauli, G., Humber, R.A., Delalibera, Jr., I. 2016. Seasonal prevalence of the insect pathogenic fungus Colletotrichum nymphaeae in Brazilian citrus groves under different chemical pesticide regimes. Fungal Ecology. 22:43-51.

Interpretive Summary: Citrus production of Sao Paulo state, Brazil, is affected by a very serious complex of insect pests and the vast majority of these pests in the great majority of Brazilian citrus orchards are routinely managed using only chemical pesticides. A small but growing movement is using biological control agents against some of these insect pests , and this paper discusses means to use fungal pathogens of insects in an integrated pest management program for the control of the scale insect pest, Praelongorthesia praelonga. The main fungus studied here has long been recognized as a significant insect pathogen and potentially useful biocontrol agent, but its identification has only now been confirmed through the use of gene-based molecular approaches as Colletotrichum nymphaeae, a species in a genus that has little previously confirmed record of activity against insects.

Technical Abstract: In a field study, we identified an endemic fungal entomopathogen, known as the 'salmão' fungus infecting populations of citrus scale, Praelongorthezia praelonga Douglas. The identification of this fungus is close to Colletotrichum nymphaeae (Sordariomycetes: Glomerellales) based on morphological similarities and the beta-tubulin-encoding protein gene (TUB2) sequences. We investigated the impact of three pest management systems on the prevalence of C. nymphaeae in commercial citrus groves. The insect management practices were distinguished based mostly on the chemical insecticide use: i.e., “intensive pesticide use” (conventional system with frequent applications of broad-spectrum chemical insecticides), “limited pesticide use” (mycoinsecticide based on Lecanicillium longisporum against P. praelonga and 75% fewer insecticidal applications), and “low pesticide use” (L. longisporum and two acaricidal applications). Other farming practices, including the use of fungicides, fertilization and pruning, were identical in all systems. Ten trees were sampled monthly in each citrus plot for presence of P. praelonga and in association with entomopathogenic fungi. Natural periodic epizootics of C. nymphaeae were observed, with infection levels up to 94 percent mortality occurring in the humid season. Mortality caused by L. longisporum ranged from 0 to 67.5 percent with higher incidence in the management with “limited pesticide use” than the others. Chemical insecticides reduced frequency of C. nymphaeae infection in the “intensive pesticide use”, possibly due to host density dependent factors. As expected, significantly higher mortality associated with other factors rather than the fungal entomopathogens was attained in the conventional system. Our data suggest that temporal patterns of insect density and infection rates by C. nymphaeae were influenced by the phytosanitary practices. Nonetheless, the prevalence of C. nymphaeae displayed a density-dependent pattern on its host, while environmental data indicated that infections by C. nymphaeae and L. longisporum were also correlated with temperature and rainfall. Our study provides circumstantial evidence that frequent use of chemical insecticides on citrus groves is inhibitory to fungal epizootics in P. praelonga.