Exposure of insects and host plants to different concentrations of CO2 affects the performance of Mahanarva spectabilis (Hemiptera: Cercopidae) in successive insect generations.

The performance of three successive generations of Mahanarva spectabilis (Distant) (Hemiptera: Cercopidae) fed on four forages exposed to environments with different CO2 concentrations was evaluated. In the first bioassay, we utilized the following scenarios: A) plants and insects were kept at high and constant CO2 (700 ppm) and B) the insects were kept at CO2 700 ppm and fed on plants from the greenhouse (average of 390 ppm). In the second bioassay, we utilized the following scenarios: C) plants and insects were kept in a greenhouse and D) the insects were kept in the greenhouse and fed on plants kept at CO2 700 ppm. The survival and duration of the nymphal and adult stages and the number of eggs/female of M. spectabilis were evaluated. It was only possible to evaluate the cumulative effects of the increase of CO2 on three successive generations of M. spectabilis kept in a greenhouse, due to the reduced survival of the insects in the first generation in the laboratory. A greater direct than indirect effect of the CO2 level on the performance of M. spectabilis was observed. Furthermore, it should be considered that the effect of CO2 elevation on the survival, periods of development, and fecundity, when taken together, can significantly impact the population dynamics of M. spectabilis in future climate scenarios.

Exposure of insects and host plants to different concentrations of CO2 affects the performance of Mahanarva spectabilis (Hemiptera: Cercopidae) in successive insect generations / A exposição de insetos e plantas hospedeiras às diferentes concentrações de CO2 afeta o desempenho de Mahanarva spectabilis (Hemiptera: Cercopidae) em sucessivas gerações do inseto

Abstract The performance of three successive generations of Mahanarva spectabilis (Distant) (Hemiptera: Cercopidae) fed on four forages exposed to environments with different CO2 concentrations was evaluated. In the first bioassay, we utilized the following scenarios: A) plants and insects were kept at high and constant CO2 (700 ppm) and B) the insects were kept at CO2 700 ppm and fed on plants from the greenhouse (average of 390 ppm). In the second bioassay, we utilized the following scenarios: C) plants and insects were kept in a greenhouse and D) the insects were kept in the greenhouse and fed on plants kept at CO2 700 ppm. The survival and duration of the nymphal and adult stages and the number of eggs/female of M. spectabilis were evaluated. It was only possible to evaluate the cumulative effects of the increase of CO2 on three successive generations of M. spectabilis kept in a greenhouse, due to the reduced survival of the insects in the first generation in the laboratory. A greater direct than indirect effect of the CO2 level on the performance of M. spectabilis was observed. Furthermore, it should be considered that the effect of CO2 elevation on the survival, periods of development, and fecundity, when taken together, can significantly impact the population dynamics of M. spectabilis in future climate scenarios.

Resumo Avaliou-se o desempenho de três gerações sucessivas de Mahanarva spectabilis (Distant) (Hemiptera: Cercopidae) alimentadas com quatro forrageiras expostas à ambientes com diferentes concentrações de CO2. No primeiro bioensaio, utilizamos os seguintes cenários: A) plantas e insetos foram mantidos em fitotron com CO2 alto e constante (média de 700 ppm) e, B) os insetos foram mantidos em nível de 700 ppm de CO2 e alimentados com plantas advindas da casa de vegetação (média de 390 ppm). No segundo bioensaio, utilizamos os seguintes cenários: C) plantas e insetos foram mantidos em casa de vegetação e, D) os insetos foram mantidos em casa de vegetação e alimentados com plantas mantidas em fitotron. A sobrevivência e duração das fases ninfal e adulta e o número de ovos/fêmea de M. spectabilis foram avaliados. Só foi possível avaliar os efeitos cumulativos do aumento do CO2 em três gerações sucessivas de M. spectabilis mantidas em casa de vegetação, devido à reduzida sobrevivência dos insetos na primeira geração quando mantidos em fitotron. Observou-se maior efeito direto do que indireto do nível de CO2 sobre o desempenho de M. spectabilis. Além disso, deve-se considerar que o efeito da elevação de CO2 sobre a sobrevivência, períodos de desenvolvimento e fecundidade, quando tomados em conjunto, podem impactar significativamente a dinâmica populacional de M. spectabilis em cenários climáticos futuros.

Biological Performance and Preference of Mahanarva spectabilis (Hemiptera: Cercopidae) for Feeding on Different Forage Plants.

The performance and preference of Mahanarva spectabilis (Distant) for feeding on different forage species were evaluated. The survival and duration of the nymphal period, longevity and fertility of adults, and food preferences (free choice) of adults of M. spectabilis were evaluated in a greenhouse trial, and food preferences of adults were also evaluated in laboratory tests without a choice of host plant. In the field, the numbers of plants with spittle masses were evaluated by forage sampling. Lower levels of nymph survival were observed in the greenhouse on Molasses grass, Jaraguá, Tanzânia, and Makueni. The duration of the nymphal period did not differ significantly on different forage species; however, the longevity and fertility of adults were significantly lower on Cynodon and Brachiaria decumbens Stapf. In the free-choice preference test, adult insects were attracted most strongly to B. decumbens and Jaraguá, with intermediate attraction to Brachiaria brizantha (Hochst ex A. Rich) Stapf and Pioneiro. In the test without host choice, insects exhibited lower excretion rates on Tanzânia, Cynodon, Jaraguá, B. brizantha, and Molasses grass, and those fed on Cynodon, Jaraguá, Molasses grass, and Makueni also exhibited reduced body mass. In the field, Pioneiro had the highest number of spittle masses, followed by Roxo de Botucatu. Thus, Molasses grass, Tanzânia, Makueni, and Jaraguá plants are less suitable food sources for M. spectabilis nymphs and adults. Additionally, although Jaraguá was less favorable to nymphs, it attracted food-seeking adults; hence, these plants have potential for use in control of M. spectabilis.

How will Mahanarva spectabilis (Hemiptera: Cercopidae) Respond to Global Warming?

The aim of this study was to determine the favorable constant temperature range for Mahanarva spectabilis(Distant) (Hemiptera: Cercopidae) development as well as to generate geographic distribution maps of this insect pest for future climate scenarios. M. spectabilis eggs were reared on two host plants (Brachiaria ruziziensis(Germain and Edvard) and Pennisetum purpureum(Schumach)), with individual plants kept at temperatures of 16, 20, 24, 28, and 32 °C. Nymphal stage duration, nymphal survival, adult longevity, and egg production were recorded for each temperature*host plant combination. Using the favorable temperature ranges for M. spectabilis development, it was possible to generate geographic distribution. Nymphal survival was highest at 24.4 °C, with estimates of 44 and 8% on Pennisetum and Brachiaria, respectively. Nymphal stage duration was greater on Brachiaria than on Pennisetum at 20 and 24 °C but equal at 28 °C. Egg production was higher on Pennisetum at 24 and 28 °C than at 20 °C, and adult longevity on Pennisetum was higher at 28 °C than at 20 °C, whereas adult longevity at 24 °C did not differ from that at 20 and 28 °C. With these results, it was possible to predict a reduction in M. spectabilis densities in most regions of Brazil in future climate scenarios.