Morphometric analyses of sexual dimorphism in sound-emitting structures in adults of the bess beetle Vindex agnoscendus (Coleoptera: Passalidae).

In insects, the sexually dimorphic body size, color, and horns are very conspicuous. Other not so obvious characteristics, such as behavioral traits related to reproduction, are also dimorphic (courtship dances and sounds). Among these, the stridulation, stridulatory apparatus, and hearing systems could also be different between sexes. Passalids are subsocial beetles with acoustic communication in the interactions of larvae-adult and adult-adult. Most of the species do not have morphological traits with sexual dimorphism, but sounds are dimorphic under reproductive and aggression contexts. We studied sexual dimorphism in the stridulation organs (plectrum) in Vindex agnoscendus (Percheron) as an important step towards understanding its functioning. We acquired SEM micrographs of the plectrum for 14 specimens per sex, for measuring size, density and shape of the spines. We performed traditional and geometric morphometric analyses to test for sexual differences in the spines of three zones (Z1-Z3) of the plectrum. Allometric analyses showed spine variation is not related to body size in either sex. Our univariate and multivariate analyses uncovered sexual dimorphism in spine size (length and width of spines), spine density (distance between spines and number of spines), and spine shape (landmark coordinates). Spines were wider in males than in females in the apical zone (Z1). The spines were further apart in females than in males in two zones (Z1, Z2) and the spine numbers were higher in females than in males in the apical zone (Z1). The shape of spines was different between sexes in two zones (Z1, Z2). Moreover, our disparity analyses showed different variability patterns in size and density of spines. Variability of spine shape was similar between sexes, and variability of spine density was higher in females than in males, while for spine size it was higher in males than in females. These findings for the plectrum suggest further research for sexual dimorphism in the pars stridens and acoustic signals, and for the possible roles of natural and sexual selection in the patterns of variability of spines.

Developmental stability, age at onset of foraging and longevity of Africanized honey bees (Apis mellifera L.) under heat stress (Hymenoptera: Apidae).

Beekeeping with the western honey bee (Apis mellifera) is important in tropical regions but scant information is available on the possible consequences of global warming for tropical beekeeping. We evaluated the effect of heat stress on developmental stability, the age at onset of foraging (AOF) and longevity in Africanized honey bees (AHBs) in the Yucatan Peninsula of Mexico, one of the main honey producing areas in the Neotropics, where high temperatures occur in spring and summer. To do so, we reared worker AHB pupae under a fluctuating temperature regime, simulating current tropical heatwaves, with a high temperature peak of 40.0 °C for 1 h daily across six days, and compared them to control pupae reared at stable temperatures of 34.0-35.5 °C. Heat stress did not markedly affect overall body size, though the forewing of heat-stressed bees was slightly shorter than controls. However, bees reared under heat stress showed significantly greater fluctuating asymmetry (FA) in forewing shape. Heat stress also decreased AOF and reduced longevity. Our results show that changes occur in the phenotype and behavior of honey bees under heat stress, with potential consequences for colony fitness.