ABSTRACT
In Argentina, the grasslands of Pampas region comprise approximately 15% of the country. As in other grasslands of the world, grasshoppers are among the most important native herbivores. Their economic importance has been recognized in Argentina since the mid to late nineteenth century, since outbreaks of different species have become recurrent phenomena. Therefore, the main objective of this work was to study their diversity and distribution in grasslands of the Southern Pampas region (Laprida county, Buenos Aires province), as one of the most affected areas. The study was conducted during five seasons (2005-10). Sampling sites were represented by the most common plant communities in this area, classified in four categories: native grasslands, disturbed grasslands, implanted pastures and halophilous grasslands. The samplings were conducted from mid-spring to early autumn, with five or six samples per season. We estimated the following population descriptors: species richness (S), eveness (E), dominance (J), and diversity index (H´). In order to evaluate the similitude of the grasshopper communities present in the different plant communities, we used qualitative and quantitative coefficients of similitude. A total of 22 species of grasshoppers were collected, of which 21 belong to the family Acrididae. The subfamily Melanoplinae was the most diverse with eight species. The largest species richness was recorded in native grasslands (18). The different communities of grasshoppers had similar indices of evenness and dominance (p>0.05). Considering all plant communities, the average value of Shannon-Wiener index was 1.58±0.075. There was a positive correlation between evenness index and species richness (p<0.05). The diversity index H’ was different between plants communities (p<0.05), and it was higher in the disturbed grassland (1.75±0.096, p<0.05) than in the halophilous grasslands (1.34±0.12). Native and disturbed grasslands had a higher plant richness than halophilous grasslands and implanted pastures (p<0.05). There was a positive relationship between plant richness and grasshoppers species richness, and diversity of grasshoppers. According to the qualitative indices applied, the similitude between different grasshopper communities was higher than 60%. In general, the species that had a higher frequency of occurrence showed greater abundance and distribution. Covasacris pallidinota, Dichroplus elongatus, D. maculipennis, Borellia bruneri and B. pallid were the most widely distributed species, most of them (12) showed a restricted distribution and few (five) an intermediate distribution.
Los acridios son componentes nativos de los pastizales, dichos sistemas han sido modificados debido a la intensificación de las actividades agrícola-ganaderas y por lo tanto se considera importante estudiar las comunidades de acridios asociadas. Se estudió la diversidad y distribución de acridios en el Sur de la región pampeana a través de muestreos realizados en las comunidades vegetales más representativas del partido de Laprida, provincia de Buenos Aires, durante cinco temporadas (2005-2010). Se recolectaron 22 especies. La subfamilia Melanoplinae fue la más diversa (ocho especies). La mayor cantidad de especies se observó en los pastizales nativos (18). La diversidad en los pastizales alterados (1.75±0.096) fue superior (p<0.05) a la de los pastizales halófilos (1.34±0.12). La riqueza de plantas en los pastizales nativos y los pastizales alterados fue superior (p<0.05) a la de las demás comunidades. Se registro una relación positiva entre la riqueza de plantas y las variables riqueza y diversidad de acridios. La similitud entre las comunidades de acridios estimada por los índices cualitativos fue superior al 60%. En general, las especies que tuvieron una mayor frecuencia de aparición, mostraron una mayor abundancia y distribución. Covasacris pallidinota, Dichroplus elongatus, D. maculipennis, Borellia bruneri y B. pallida fueron las de mayor distribución, cinco especies tuvieron una distribución intermedia y la mayoría (12) una distribución restringida.
Subject(s)
Animals , Biodiversity , Grasshoppers/classification , Poaceae , Argentina , Population Density , Population DynamicsABSTRACT
Dichroplus maculipennis is one of the most characteristic and damaging grasshopper species of Argentina, mainly in areas of the Pampas and Patagonia regions. We estimated and compared the longevity and fecundity of adult female D. maculipennis under controlled conditions (30ºC, 14L:10D, 40 percent RH) from individuals collected as last instar nymphs (VI) in the field and with a known recent history of low and high density conditions. Densities of D. maculipennis at the collecting sites were 0.95 individuals per m² in 2006 and 46 ind/m² in 2009, representing non-outbreaking and outbreaking situations, respectively. Adult female longevity in 2006 (67.96 ± 3.2 days) was significantly higher (p < 0.05) than in 2009 (37.44 ± 1.98 days). The number of egg-pods per female was 3.32 ± 0.44 for 2006 and 1.62 ± 0.26 for 2009. The average fecundity in 2006 (89.29 ± 11.9 eggs/female) was significantly greater (p < 0.05) than that in 2009 (36.27 ± 5.82 eggs/female). While it was observed that the oviposition rate was higher in 2006, this difference was not significant (p > 0.05). The fecundity curves showed that the highest values were at weeks 11 and 13 for the 2006 females, and at week 6 for those of 2009. Since the daily oviposition rate at low and high densities was not significantly different, the diminished fecundity rate at high density is attributable to their reduced longevity.
O gafanhoto Dichroplus maculipennis é um dos mais característicos e prejudiciales da Argentina, principalmente nas regiões das Pampas e da Patagonia. O objetivo deste estudo foi estimar e comparar a longevidade e fecundidade das fêmeas adultas do D. maculipennis sob condições controladas (30ºC, 14 luz: 10 obscuridad, 40 por cento RH) a partir do indivíduos coletados em campo como ultimo estadio ninfal (VI) e con historia recente conocida de baixas e altas densidades. As densidades de D. maculipennis nos locais de coleta foram de 0.95 indivíduos por m² em 2006 e 46 indivíduos/m² em 2009, representando situações de "non-outbreaking" e "outbreaking", respectivamente. A longevidade das fêmeas adultas em 2006 (67.96 ± 3.2 dias) foi significamente maior (p < 0.05) do que as de 2009 (37.44 ± 1.98 dias). O número de oviposiçãos por fêmea foi de 3.32 ± 0.44 para 2006 e 1.62 ± 0.26 para 2009. A fecundidade média em 2006 (89.29 ± 11.9 ovos/fêmea) foi significativamente maior (p < 0.05) do que a das fêmeas de 2009 (36.27 ± 5.82 ovos/fêmea). As curvas de fecundidade mostraram que os valores mais elevados ocorreram nas 11ª e 13ª semanas de 2006, e na 6ª semana para àquelas de 2009. Comparando a taxa diária de oviposição para altas e baixas densidades, não apresentaram diferenças significativas (p > 0.05). No entanto, as baixas taxas de fecundidade das fêmeas em densidades elevadas, se devem, provavelmente à longevidade reduzida.