Interação de Mahanarva spectabilis (Distant, 1909) e forrageiras: desempenho biológico e preferência alimentar

Abstract

Mahanarva spectabilis (Distant, 1909) is a pest that limits the production of forage grass in Brazil. Current study evaluated the influence of different forage grass on biological performance, feed preference and olfactory response of M. spectabilis. Biological aspects and food preference (free choice) of M. spectabilis were evaluated in a greenhouse; and food preference (without choice) in the laboratory. In the field, forages with spittle masses were sampled. Olfactory responses of M. spectabilis were evaluated in "Y" olfactometer, for forages without and with M. spectabilis injury and its extracts. Finally, a chemical analysis of the compounds released by forages with and without injury was conducted. Significant differences in the biological performance of M. spectabilis have been registered in different foragers, with lowest nymphal survival rate in Capim Gordura, Jaraguá, Tanzânia and Makueni and low adult longevity and fertility in Cynodon and Brachiaria decumbens Stapf. Feed preference tests with choice revealed greater attractiveness to B. decumbens and Jaraguá, whereas excretion rate was lower for Tanzânia, Cynodon, Jaraguá and Brachiaria brizantha (Hochst ex A. Rich) Stapf in the test without choice. Field experiment demonstrated high amounts of foam with nymphs in Pioneiro and Roxo de Botucatu. In Olfactometer tests, M. spectabilis showed preference for volatiles of B. decumbens and Pioneiro without injury, and repellency for volatiles of B. brizantha with injury of co-specifics. Analyses of the chemical profile of forage organic compounds showed that emissions of plant volatiles with and without injury by M. spectabilis are different. Plants with injury emitted a greater number of compounds when compared to non-injured plants. Current research underscores that forage grasses Capim gordura, Tanzânia, Makueni and Jaraguá inhibit feed and the development of M. spectabilis, and thus the capacity of using them as plants resistant to M. spectabilis, including in plant diversification. Further, M. spectabilis employs the plants chemical clues in its choice of hosts and may contribute towards the adoption of management strategies integrated to the pest, especially with the use of pest-repelling compounds.