In the study of the chemical communication of adults of the Melolonthidae family, bacteria have been observed in the epithelium of the genital chamber; possibly, bacteria are involved in the production of sex attractants in their hosts. Therefore, it is important to identify the volatile organic compounds from bacteria (VOCsB) released by these microorganisms and study the biological activity stimulated by VOBCs in adults of Melolonthidae. In this study, bacteria were isolated from the genital chamber of Cyclocephala lunulata and Cyclocephala barrerai, from which VOCsB were extracted using static headspace solid-phase microextraction (SHS-SPME) and dynamic headspace Super Q solid-phase extraction (DHS-SPE) and analyzed using gas chromatography-mass spectrometry. The effect of VOCsB on the hosts and conspecifics was evaluated utilizing an olfactometer and electroantennography (EAG). Two species of Enterobacteria were isolated from the genital chamber of each female species, and VOCsB derived from sulfur-containing compounds, alcohols, esters, and fatty acids were identified. An attraction response was observed in olfactometry studies, and antennal responses to VOCsB were confirmed in EAG bioassays. With these results, new perspectives on the relationship between these beetles and their bacteria emerge, in addition to establishing a basis for management programs in the future.

The Order Coleoptera provides good examples of morphological specializations in the reproductive apparatus, gonadic maturation, and allometry differing between the sexes. The female and male reproductive apparatus has been modified to ensure reproduction between individuals of the same species. The genus Cyclocephala has more than 500 species distributed in America, and Cyclocephala barrerai Martínez is an economically important species in the central part of Mexico. The objective of this work was to study the reproductive system, gonadic maturation, and allometry of C. barrerai. We used light, scanning electron, and laser scanning confocal microscopy to describe the reproductive apparatus and gonadic maturation of females and males. The relationship between adult weight and different parts of the body was established by linear regression. Regardless, the reproductive apparatuses of C. barrerai are like those of other Melolonthidae: the genital chamber, the type II accessory glands, and the ventral plaques of the female and the ejaculator bulb and genital capsule of the males are specific to C. barrerai. The gonads are fully developed when 18 d old. The weight of adult C. barrerai has a positive linear relationship with distinct parts of its body, while the antennae of males are larger than those of the females.

Scarab beetles use pheromones and volatiles to search for their partners and host plants. The perception of these compounds occurs in the beetle antennae, particularly in the sensilla. Relatively few studies have morphologically and physiologically characterized the sensilla of scarab beetles. Cyclocephala barrerai Martínez is a beetle distributed in Mexico. Male beetles have larger antennal lamellae than females, and in both cases, the size of this structure is related to their weight. Previous studies have reported that both sexes are attracted to bacterial volatiles isolated from the female genital chambers. Female cuticular hydrocarbons may act as a sexual contact pheromone. However, antennal sensilla and their electrophysiological responses to behaviorally relevant compounds remain to be investigated. Here, we describe and report the types, allometric relationships, and functions of sensilla found in the lamellae of both C. barrerai sexes. Sensilla were identified, classified, measured, and counted to identify intra and intersexual relationships. The single sensillum recordings showed that plant volatiles, hydrocarbons, and heat stimulated receptor neurons. We identified 2 new types of sensilla basiconica in the scape. Males have more and larger antennal sensilla placodea IV, which specializes in detecting pheromones, plant volatiles, and heat. Females have a greater diversity of sensilla.

A major challenge in studying the biology of the Melolonthidae has been the lack of a consistent supply of organisms with known characteristics. This study aimed to develop a methodology for mass-rearing a Cyclocephala barrerai Martínez (Coleoptera: Melolonthidae) colony over several laboratory generations. The mass-rearing was initiated with eggs from wild-collected adults; each developmental instar was reared under conditions suited to their environmental and nutritional needs. Insect survival, egg-adult cycle length, sex ratio, adult weight, and number of eggs laid by each female were recorded for each generation. The morphology of mass-rearing organisms was compared to that of the wild-collected specimens. A second cohort of organisms from the original generation was reared under identical conditions and their survival, duration, and morphometry of each larval instar were recorded weekly. These data were then compared to those from the original group to assess the impact of constant manipulation during the larval instar. The mass-rearing methodology proposed in this work successfully reared 3 generations of C. barrerai with an overall average egg-adult survival rate of 66.6%. The egg-adult cycle length, proportion of females and males, and average weight differed among generations. The F1 organisms presented similar morphometrics to those collected in the field. Manipulation significantly reduced insect survival. Mass-rearing of C. barrerai facilitates a comprehensive study of its biology and may establish the species as a model for the Melolonthidae. This methodology establishes the foundations for rearing congeneric species in the laboratory.

Our study aimed to characterize mating behavior in virgin and once-mated males and females of Cyclocephala barrerai. We reared the specimens under laboratory conditions and recorded the age at which the organisms began their reproductive activity and the time they remained active. We characterized behavioral acts during mating in two groups—virgin and once-mated organisms. Transitions between behaviors were analyzed using Markov chains and the generated ethograms. The duration of behaviors and the percentage of transitions were compared between the two groups. To characterize the mating behavior of C. barrerai, we adopted a framework commonly used in the literature, dividing mating behavior into three phases: premating, mating, and postmating. (A) Premating: Males search for females and mount and stimulate them, which the females resist through fighting behaviors. (B) Mating: The male mounts the female, which moves around and then stops; the male performs specific movements of the antennae and head and inserts his aedeagus into the female. (C) Postmating: Males exhibit guarding behavior over females. Although differences in pre- and postmating behaviors were observed between virgin and once-mated organisms, the duration of the acts did not show significant differences. These results provide key information on the reproductive behavior of C. barrerai, contributing to a better understanding of their biology and sexual interaction patterns.