Interaction of spittlebug and forage grass under different carbon dioxide concentrations

Abstract

This study evaluated the impact of different CO2 levels on the biological characteristics of Mahanarva spectabilis (Distant) and on the performance of forage grasses. The signal grasses Brachiaria decumbens Stapf (susceptible) and Brachiaria brizantha (A. Rich.) (resis- tant), the elephant grass Pennisetum purpureum (Schum.), including the Roxo de Botucatu cultivar (susceptible) and the Pioneiro cultivar (resistant) and the insects were kept in climate-controlled chambers with constant low (250 ppm) CO2 levels, constant high (500 ppm) CO2 levels, or fluc- tuating CO2 levels (mean, 368 ppm). Among these three CO2 treatments, no significant differences were found in the nymphal survival of M. spectabilis when the nymphs were fed on two signal grass species. On the other hand, under a constant low CO2 level (250 ppm), nymphal sur- vival rates were significantly lower when the insects were kept in Roxo de Botucatu and Pioneiro cultivars. The mean adult longevity values for M. spectabilis were not signifi- cantly different among the three levels of CO2 evaluated. We observed that increased CO2 levels improved the per- formance of M. spectabilis and elephant grass cultivars in accumulating dry mass, which was not evident in signal grass. We further conclude that the levels of susceptibility and resistance of the forages tested will be maintained in future scenarios under which atmospheric CO2 levels are expected to increase.