Sex ratios in juveniles and adults of Dichroplus maculipennis (Blanchard) and Borellia bruneri (Rehn) (Orthoptera: Acrididae)

Abstract

Revista Brasileira de Entomologia 59 (2015) 96-99 w w w . r b e n t o m o l o g i a . c o m a b s t r a c tDichroplus maculipennis and Borellia bruneri are two of the 18 grasshopper species of actual or potential economic relevance as pests in Argentina. The objective of this study was to estimate the sex ratios for adults and older nymphs of D. maculipennis and B. bruneri in the field, and analyze possible temporal variations. The study was conducted during seven seasons (2005-06 to 2011-12) in representative plant communities of the southern Pampas region. A total of 4536 individuals of D. maculipennis, and 6038 individuals of B. bruneri were collected. The sex ratio registered in older nymphs for D. maculipennis and B. bruneri did not deviate from a 1:1 ratio (p > 0.05), suggesting that these species have such a primary sex ratio. However, a significant bias in sex composition in adults of both species was observed (p < 0.05). The sex ratio in adults of D. maculipennis was different in five of the 18 sampling dates carried out. In three sampling dates it was biased toward males, while in the other two it was biased toward females. Taking into account the sex ratio by sampling season, significant differences were recorded in two seasons. In 2007-08 the sex ratio was biased toward males (1 F:2.26 M), while in 2008-09 it was biased toward females (1.35 F:1 M). The sex ratio in adults of B. bruneri was always biased toward males (p < 0.05). We conclude that results obtained in this study indicate that various factors like differential survival, dispersion, predation, among others, could have modified the primary sex ratio in these species.

Morphometric Differentiation in a Field Population ofDichroplus maculipennis(Orthoptera: Acrididae: Melanoplinae) under Outbreak and Non-Outbreak Situations

“…likewise, studies under experimental, controlled conditions determined that females from outbreak conditions have a shorter lifespan and are less fecund than females from non-outbreak conditions (Mariottini et al 2011c), conceivably accounting for the physiology "expression". Since no color differences were observed in more than 1500 juveniles at outbreak and non-outbreak conditions (Mariottini et al 2015) and no records (even anecdotal or circumstantial) exist in the earlier literature that mention coloration changes in nymphs, nymphal color "expression" is the only lacking characteristic preventing D. maculipennis from exhibiting the complete set of evidence of density-dependence phase polyphenism.…”

Postembrionic development and reproductive parameters of the grasshopper pest Borellia bruneri (Acrididae: Gomphocerinae) under controlled conditions

“…In recent years, several studies carried out in Argentina and Uruguay have contributed valuable information regarding B. bruneri, such as its distribution, density, sex ratio, and nymphal morphometry (De Wysiecki et al, 2011;Mariottini et al, 2012Mariottini et al, , 2015Miguel et al, 2014;Zerbino et al, 2016). Nevertheless, important aspects related to the biology and ecology are still unknown.…”