The role of the host-specific grasshopper Cornops aquaticum (Orthoptera: Acrididae) as consumer of native Eichhornia crassipes (Pontederiaceae) floating meadows

Cornops aquaticum is a widely distributed semiaquatic grasshopper in the Neotropics. The development, feeding and oviposition of C. aquaticum take place on Pontederiaceae, especially on species of Eichhornia. Several aspects of the feeding of C. aquaticum are studied because is one of the most important herbivores of the highly invasive floating Eichhornia crassipes in native areas. The aims of this paper were: (1) to quantify the amount of E. crassipes consumed by C. aquaticum, (2) to determine the growth rate and the conversion efficiency of food ingested by this grasshopper, and (3) to determine the possible effect of consumption on E. crassipes productivity. Thirty individuals from each specific age class were used in the experiment: nymphs A, nymphs B, adult males and adult females. Insects were individually confined in plastic pots with a leaf of E. crassipes. We estimated feeding by individual, consumption index (CI), relative growth rate (GR) and efficiency of conversion of ingested food to body substance (ECI). The impact of C. aquaticum consumption on E. crassipes floating meadows was assessed with the abundance of the grasshopper, and the available data on primary production of the host plant at the study site. Food intake of C. aquaticum was 11.23% of plant productivity. Food consumption, growth rate and food conversion efficiency of this grasshopper varied according to the specific age classes. Damage caused by C. aquaticum is high in comparison with the damage caused by other semiaquatic and grassland grasshoppers, however it is not enough to prevent the growth and coverage of native E. crassipes floating meadows because abundance of grasshoppers are realtively low and the growth rate and productivity of the host plant is high. Rev. Biol. Trop. 59 (3): 1407-1418. Epub 2011 September 01.

Cornops aquaticum es una tucura semiacuática Neotropical que vive asociada a las Pontederiaceae y constituye uno de los más importantes herbívoros de Eichhornia crassipes en áreas nativas. Los objetivos de este trabajo son: (1) cuantificar el consumo de C. aquaticum (2) determinar la tasa de crecimiento y la eficiencia de conversión del alimento ingerido de esta tucura, y (3) determinar el efecto del consumo en la productividad de E. crassipes. De cada categoría de edades de la población se utilizaron 30 individuos: ninfas A, ninfas B, adultos machos y hembras. Los insectos fueron confinados individualmente en recipientes con hojas de E. crassipes. Luego, se estimó el consumo por individuo, la tasa de consumo (CI), tasa de crecimiento (GR) y la eficiencia de conversión del alimento (ECI). La abundancia de C. aquaticum se determinó en verano y con los datos de productividad de la planta se calculó el efecto del consumo sobre E. crassipes. La tasa de consumo, tasa de crecimiento y la eficiencia de conversión del alimento varió entre las distintas categorías de edades de la población. C. aquaticum consume el 11% de la productividad primaria de E. crassipes. Si bien el consumo es alto, el daño no produce mermas importantes en los camalotales debido a la abundancia relativamente baja de C. aquaticum y la alta productividad de la planta huésped.

Metaphase I orientation of Robertsonian trivalents in the water-hyacinth grasshopper, Cornops aquaticum (Acrididae, Orthoptera)

Trivalents resulting from polymorphic Robertsonian rearrangements must have a regular orientation in metaphase I if the polymorphisms are to be maintained. It has been argued that redistribution of proximal and interstitial chiasmata to more distal positions is necessary for a convergent orientation, the only one that produces viable gametes. Cornops aquaticum is a South-American grasshopper that lives and feeds on water-hyacinths, and has three polymorphic Robertsonian rearrangements in its southernmost distribution area in Central Argentina and Uruguay. The orientation of trivalents in metaphase I, the formation of abnormal spermatids and the frequency and position of chiasmata in the trivalents, was analysed in a polymorphic population of C. aquaticus. In this study we observed a correlation between the number of trivalents with the frequency of abnormal spermatids; additionally, the number of chiasmata, especially proximal and interstitial ones, was strongly correlated with the frequency of the linear orientation. Therefore we confirmed our previous assumption, based on other evidence, that the chiasmata redistribution in fusion carriers is essential to the maintenance of the polymorphisms.

Duração do ciclo de vida de Cornops aquaticum (Bruner, 1906) (Orthoptera: Acrididae: Leptysminae) e aspectos de seu comportamento alimentar na Amazônia central / Life cycle of Cornops aquaticum (Bruner, 1906) (Orthoptera: Acrididae: Leptysminae) and aspects of its food behavior at Central Amazonia

O gafanhoto Cornops aquaticum (Bruner, 1906) (Orthoptera: Acrididae: Leptysminae) completa seu ciclo de vida em Eichhornia (Pontederiaceae). Em experimentos ao ar livre, durante o período da enchente, foi verificado que a cópula pode durar entre 40 a 120 minutos. Cada postura tem em média 13,4 ovos (+/- 3,2) e o período de incubação durou 34,1 dias (+/- 1,97). A duração média do desenvolvimento de ovo a adulto foi de 156,2 dias, sendo 34,1 do estágio de ovo, 53,4 do estágio ninfal e 68,7 do estágio adulto. Alimentou-se de 6 espécies de macrófitas aquáticas dentre as 13 oferecidas. Ninfas (N) e Adultos (A) sobreviveram mais dias em Pistia stratiotes (N = 43 por cento até 30 dias e A =1 por cento até 27 dias) e Pontederia sp. (N = 85 por cento e A = 40 por cento até 24 dias) que em Limnobium sp. (N =13 por cento e A =10 por cento até 12 dias), Ludwigia sp. (N =3 por cento até 24 dias e A =15 por cento até 9 dias), Azolla sp. (N =35 por cento até 9 dias e A =15 por cento até 12 dias) e Paspalum repens (N =3 por cento até 21 dias e A =5 por cento até 24 dias).

Life cycle of the grasshopper Cornops aquaticum (Bruner, 1906) (Orthoptera: Acrididae: Leptysminae) is dependent on Eichhornia (Pontederiaceae). Experiments were carried outdoors during receding water, the Mating last for about 40 and 120 minutes. The ootheca has an average of 13.4 (+/- 3.2) eggs. Incubation lasted for 34.1 days (+/- 1.97). Mean durations of total development from egg to adult was 156.2 days, being 34.1 in the egg stage, 53.4 in the ninphal stage, and 68.7 in the adult stage. Nymphs (N) and adults (A) accepted only six aquatic macrophytes out of 13 species offered during 30 days; survived more time in Pistia stratiotes (N = 43 percent, 30 days and A = 1 percent, 27 days) and Pontederia sp. (N = 85 percent and A = 40 percent until 24 days) than Limnobium sp. (N =13 percent and A =10 percent until 12 dias), Ludwigia sp. (N =3 percent, 24 days and A =15 percent, 9 days) Azolla sp. (N =35 percent, 9 days and A =15 percent, 12 days) and Paspalum repens (N =3 percent, 21 days and A =5 percent, 24 days).