Cuticular lipid profiles of selected species of cyclocephaline beetles (Melolonthidae, Cyclocephalini).

Neotropical cyclocephaline beetles, a diverse group of flower-loving insects, significantly impact natural and agricultural ecosystems. In particular, the genus Cyclocephala, with over 350 species, displays polymorphism and cryptic complexes. Lacking a comprehensive DNA barcoding framework, accessible tools for species differentiation are needed for research in taxonomy, ecology, and crop management. Moreover, cuticular hydrocarbons are believed to be involved in sexual recognition mechanisms in these beetles. In the present study we examined the cuticular chemical profiles of six species from the genus Cyclocephala and two populations of Erioscelis emarginata and assessed their efficiency in population, species, and sex differentiation. Overall we identified 74 compounds in cuticular extracts of the selected taxa. Linear alkanes and unsaturated hydrocarbons were prominent, with ten compounds between them explaining 85.6% of species dissimilarity. Although the cuticular chemical profiles efficiently differentiated all investigated taxa, only C. ohausiana showed significant cuticular profile differences between sexes. Our analysis also revealed two E. emarginata clades within a larger group of 'Cyclocephala' species, but they were not aligned with the two studied populations. Our research underscores the significance of cuticular lipid profiles in distinguishing selected cyclocephaline beetle species and contemplates their potential impact as contact pheromones on sexual segregation and speciation.

Can Pheromones Contribute to Phylogenetic Hypotheses? A Case Study of Chrysomelidae.

Pheromones mediate species-level communication in the search for mates, nesting, and feeding sites. Although the role of pheromones has long been discussed by various authors, their existence was not proven until the mid-twentieth century when the first sex pheromone was identified. From this finding, much has been speculated about whether this communication mechanism has acted as a regulatory agent in the process of speciation, competition, and sexual selection since it acts as an intraspecific barrier. Chrysomelidae is one of the major Phytophaga lineages, with approximately 40,000 species. Due to this immense diversity the internal relationships remain unstable when analyzed only with morphological data, consequently recent efforts have been directed to molecular analyses to establish clarity for the relationships and found their respective monophyly. Therefore, our goals are twofold 1) to synthesize the current literature on Chrysomelidae sex pheromones and 2) to test whether Chrysomelidae sex pheromones and their chemical structures could be used in phylogenetic analysis for the group. The results show that, although this is the first analysis in Chrysomelidae to use pheromones as a phylogenetic character, much can be observed in agreement with previous analyses, thus confirming that pheromones, when known in their entirety within lineages, can be used as characters in phylogenetic analyses, bringing elucidation to the relationships and evolution of organisms.

Feeding on the Fruit Waste Orange Bagasse Modifies Immature Protein Content, Body Weight, Scent Bouquet Composition, and Copula Duration in Males of a Tephritid Frugivorous Fly.

Anastrepha ludens is a polyphagous frugivorous tephritid that infests citrus and mango. Here, we report the establishment of a laboratory colony of A. ludens reared on a larval medium that is a waste for the citrus industry, specifically, orange (Citrus × sinensis) fruit bagasse. After 24 generations of rearing on a nutritionally poor orange bagasse diet, pupae weighed 41.1% less than pupae from a colony reared on a nutritionally rich artificial diet. Larvae from the orange bagasse diet had 6.94% less protein content than larvae from the artificial diet, although their pupation rate was similar. Males from the orange bagasse diet produced a scent bouquet with 21 chemical compounds and were sexually competitive, but they had significantly shorter copulations when compared to males from the artificial diet and from the wild host, Casimiroa edulis, which had relatively simple scent bouquets. The chemical complexity in the odors of males from the orange bagasse diet might initially have attracted females to novel scent combinations, but, once in the copula, they may have been able to sense negative characteristics in males, leading them to terminate copulations soon after they began. We conclude that A. ludens can adjust morphological, life history, nutritional, and chemical traits when adapted to a larval environment consisting of fruit bagasse.

Semiochemicals Associated with the Western Flower Thrips Attraction: A Systematic Literature Review and Meta-Analysis.

The study of the semiochemicals of the western flower thrips (WFT), Frankliniella occidentalis, Pergande (Thysanoptera: Thripidae), is a relevant topic that spans the last two decades. Approximately a hundred articles published on this subject from 2000 to 2022 can be found in academic databases, representing approximately 5% of the research on this important pest. These topics have generated a platform for novel research with a high potential for development. However, to move on to a new research step, an effectiveness evaluation of the compounds discovered so far is necessary. This review conducted a systematic analysis of the research focused on the semiochemicals (kairomones, pheromones, and attractants) for this pest. Papers from the past three decades on WFT attraction to semiochemicals were collected from databases using the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. The number of individuals attracted to compounds was extracted from the papers and compiled for analysis. With this information, an attraction ratio was calculated. Forty-one possible attractants were found in the literature, with methyl isonicotinate being the most-studied compound so far, with the third-highest attraction ratio. δ-Decalactone was the compound with the highest attraction ratio, but it was one of the least studied. A meta-analysis of the WFT choosing proportion was performed for the compounds with more trials found in the literature. The predicted mean choice percentages for methyl isonicotinate (MIN) and Lurem-TR, the MIN's commercial product, were 76.6% and 66.6%, respectively. There was a convergence among the analyzed studies showing a high degree of research focus on the same group of nitrogen-containing compounds (mainly the pyridine structure). These findings call for future research to diversify the discovery and evaluation of attractive compounds in this relevant study area.

Antennal sensilla of two species of Gymnetis MacLeay, 1819 (Coleoptera: Scarabaeidae: Cetoniinae)

ABSTRACT The present study describes the morphology of the antennal sensilla of adults of Gymnetis holosericea (Voet, 1779) and Gymnetis rufilateris (Illiger, 1800). The adults of Gymnetis spp. were sexed and antenna of males and females were dissected. Both species have sensilla chaetica, trichodea, placodea (type I and II), coeloconica (type I and II), and ampullacea (or pore). Females of G. holosericea have a total of about 19,995 sensilla and males have about 23,273 sensilla, and females of G. rufilateris have about 16,633 sensilla and males have about 21,184 sensilla. Sensilla placodea are the predominant type of sensilla in males and females of G. holosericea and G. rufilateris.

Pheromone Activity after Stimulation with Ampicillin in a Plasmid-Free Enterococcus faecalis Strain.

Enterococci exhibit clumping under the selective pressure of antibiotics. The aim of this study was to analyze the effect of supernatants from a plasmid-free clone (C29) of Enterococcus faecalis subjected to 0.25×, 0.5×, and 0.75× of the minimal inhibitory concentration (MIC) of ampicillin on the expression of an aggregation substance (AS) by a donor plasmid clone (1390R). A clumping assay was performed. The relative expression of prgB (gene that encodes AS) was determined and semiquantified in 1390R, and iad1 expression was determined and semiquantified in C29. AS expression was analyzed in the stimulated 1390R cells by confocal microscopy, flow cytometry, and ELISA. Adherence was also measured. Maximal clumping was observed with the pheromone medium 0.25×. Only the 1390R strain stimulated with the C29 supernatant without ampicillin and with 0.25× was able to express prgB. No expression of prgB was observed at 0.5× and 0.75×. The difference in relative expression (RE) of 1390R without ampicillin and with 0.25× was 0.5-fold. AS expression in 1390R showed the greatest increase upon stimulation with 0.25×. When 1390R was stimulated with 0.5× and 0.75×, AS expression was also observed but was significantly lower. Ampicillin stimulated C29 switch-off pheromone expression in recipient cells, which in turn switched off AS expression in donor cells. We observed that although prgB was switched off after 0.5× stimulation in C29, the supernatants induced expression in certain 1390R strains. In conclusion, ampicillin was able to modulate pheromone expression in free plasmid clones which, in turn, modulated AS expression in plasmid donor cells. The fact that PrgB gene expression was switched off after the ampicillin stimulus at 0.5× MIC, whereas AS proteins were present on the surface of the bacteria, suggested that a mechanism of rescue associated with mechanism pheromone sensing may be involved.

Cuticular hydrocarbons as caste-linked cues in Neotropical swarm-founding wasps.

Wasps (Vespidae) are important organisms to understand the evolution of social behaviour. Wasps show different levels of sociality, which includes solitary to highly eusocial organisms. In social insect species, queens and workers differ in physiology and morphology. The Neotropical swarm-founding wasps (Epiponini) show a variety of caste syndromes. In this clade, the caste-flexibility is a unique characteristic, in which workers can become queens and swarm to start a new nest. The investigation of the caste system comparing several Epiponini species show a clear-cut morphological distinction between queens and workers, with a morphological continuum between queens and workers. However, whether cuticular hydrocarbons (CHCs) are used as cues for caste recognition in swarm-founding wasps is still unknown. We studied whether CHCs may display caste-linked differences in eleven species of Epiponini wasps and if CHCs differences would follow morphological patterns. Our results suggest that queens and workers of Epiponini wasps are chemically different from each other at two levels, qualitatively and quantitatively, or merely quantitatively. This variation seems to exist regardless of their morphological traits and may be useful to help us understanding how chemical communication evolved differently in these species.

Temperature increase impairs recognition among nestmates in the social wasp Polybia paulista H. von Ihering, 1896 (Vespidae: Polistinae: Epiponini)

Cuticular hydrocarbons (CHCs) of most terrestrial arthropods primarily serve as a protective barrier against desiccation and infection. Throughout evolution, these compounds have acquired another fundamental function: the exchange of signals during interactions between nestmates. However, even though cuticular hydrocarbons perform a dual function in social insects, little is known about the effect(s) of one function on the other in social insects, and no study has evaluated this relationship in social wasps. Therefore, the present study tests the hypothesis that the level of aggressiveness presented during induced encounters between nestmates of Polybia paulista who were subjected to different conditions temperature is different than between nestmates who remained under the same temperature conditions. If the hypothesis is confirmed, it is likely because the cuticle of the wasps that had been exposed to temperature variation adjusted to these conditions leading them not to recognize the cuticular chemical signature of their colony. To test this hypothesis, workers were exposed to temperature variation in a BOD chamber and then subjected to encounters with workers who were maintained at a constant temperature of 24℃. We also used control groups to evaluate the effect of isolation alone among the groups. According to our results, our hypothesis was confirmed, the level of aggressiveness presented between nestmates who were exposed to temperature variation and those who remained at 24℃ was significantly higher than the levels of aggressiveness presented between nestmates who remained isolated but under constant temperature during the same period, in some cases, it was similar to the aggressiveness presented in encounters between wasps from different colonies. During these encounters, wasps performed alarm behavior, bites, and stings not seen during encounters between wasps that remained under the same temperature, but in isolated groups. The lack of aggressive behavior under isolated conditions indicates that isolation had no effect on chemical recognition signature. These results suggest that temperature variation may have caused some change in the cues that allow recognition between nestmates. On the other hand, these results were not caused by isolation or stress generated by the study design and difference in the CHC profile of workers, as described in the literature, is consistent with our results.(AU)

Aggregation Pheromones of Weevils (Coleoptera: Curculionidae): Advances in the Identification and Potential Uses in Semiochemical-Based Pest Management Strategies.

With approximately 83,000 species described, Curculionidae is the largest family of beetles, comprising more than 80% of all weevil species worldwide. Many species of Curculionidae attack a wide range of native and orchards crops, as well as globally important stored products such as grains, flour, and seeds, being responsible for significant environmental and economic losses. This work provides an overview of the research in the identification of aggregation pheromones of Curculionidae, and their potential contributions to the development of semiochemical-based pest management strategies. The synergistic effect of the host plant volatiles in the attractiveness of weevil pheromones is also briefly reported, demonstrating the important role of these additional attractants in the chemical communication of curculionids.

Mating Disruption of Pseudococcus calceolariae (Maskell) (Hemiptera, Pseudococcidae) in Fruit Crops.

Pseudococcus calceolariae, the citrophilous mealybug, is a species of economic importance. Mating disruption (MD) is a potential control tool. During 2017-2020, trials were conducted to evaluate the potential of P. calceolariae MD in an apple and a tangerine orchard. Two pheromone doses, 6.32 g/ha (2017-2018) and 9.45 g/ha (2019-2020), were tested. The intermediate season (2018-2019) was evaluated without pheromone renewal to study the persistence of the pheromone effect. Male captures in pheromone traps, mealybug population/plant, percentage of infested fruit at harvest and mating disruption index (MDI) were recorded regularly. In both orchards, in the first season, male captures were significantly lower in MD plots compared to control plots, with an MDI > 94% in the first month after pheromone deployment. During the second season, significantly lower male captures in MD plots were still observed, with an average MDI of 80%. At the third season, male captures were again significant lower in MD than control plots shortly after pheromone applications. In both orchards, population by visual inspection and infested fruits were very low, without differences between MD and control plots. These results show the potential use of mating disruption for the control of P. calceolariae.

Bioactive Male-Produced Volatiles from Anastrepha obliqua and their Role in Attraction of Conspecific Females.

The study of insect semiochemicals, especially pheromones, is of fundamental importance for the development of strategies for controlling agricultural pests. In this study, volatile compounds involved in the communication between males and females of the fruit fly, Anastrepha obliqua (Diptera: Tephritidae), for mating purposes were characterized to develop attractant formulations for females of this species. Extracts containing volatile compounds released by males of A. obliqua were obtained by the dynamic headspace technique and analyzed by gas chromatography coupled with an electroantennographic detector (GC-EAD) and gas chromatography coupled with mass spectrometry (GC-MS). Twenty-one volatile compounds were identified in the aeration extracts of males. Five of them caused EAD responses from the antennae of females: 1-heptanol, linalool, (Z)-3-nonen-1-ol, (E,Z)-3,6-nonadien-1-ol, and (Z,E)-α-farnesene. Six synthetic mixtures of these compounds, including the five-component blend and all possible four-component blends, were formulated in a biopolymer and used in behavioral bioassays conducted in the laboratory arena with conspecific virgin females. One blend of 1-heptanol, linalool, (Z)-3-nonen-1-ol, and (Z,E)-α-farnesene attracted more females than the collection of volatiles from virgin males used as control. The other mixtures were as attractive to A. obliqua females as the control treatment. This study indicates potential for use of these compounds in monitoring and control strategies for this pest.

Profile of Terpenoid Compounds Mediating a Plant-Herbivore Interaction: Screening by Static Headspace Solid-Phase Microextraction-Gas Chromatography/Q-ToF Mass Spectrometry.

Conotrachelus dimidiatus (Coleoptera: Curculionidae) interacts with immature guava fruits (Psidium guajava L.) for feed, sleep, mate and oviposit. Determination of the volatile organic compounds (VOCs) emitted by the insect and immature fruits can help improve understanding of plant-insect and intraspecific insect interactions between females and males of C. dimidiatus. Daytime fruit setting emissions of immature guava consist mainly of limonene, caryophyllene, and aromadendrene. In addition to the host's volatiles, the aim of this study was to assess the VOCs released by the insect. Static headspace-solid phase microextraction (SHS-SPME), combined with gas chromatography/quadrupole time of flight mass spectrometry (GC/Q-ToF-MS), allowed the identification of the C10 terpenoids: grandlure I, II, II, IV, grandisoic acid, papayanol and papayanal bioactive compounds released by female and male C. dimidiatus under laboratory conditions. These chemical compounds are candidates for the preparation of a lure formulation.

Tergal Gland Secretion of the Rove Beetle Aleochara pseudochrysorrhoa (Staphylinidae: Aleocharinae): Chemical Composition and Biological Roles.

Aleochara pseudochrysorrhoa has a glandular complex known as the tergal gland. Generally, the tergal gland secretion (TGS) has been described to have defensive function, but some reports point to a possible secondary function of this complex. For example, the TGS of the related species A. curtula has been demonstrated to possess an important role in intraspecies communication. In this work, we describe the chemical composition of the TGS of A. pseudochrysorrhoa males and females. Eleven compounds were identified based on GC/MS and GC-FT-IR analyses, retention indexes and derivatization products. Furthermore, a brief study regarding the biological function of the TGS in mating behavior is provided, in which the stimulation of male grasping response reaction by female TGS proved to be dependent on concentration.

GnRHa implants and size pairing effects on plasma and cephalic secretion sex steroids in Arapaima gigas.

Arapaima gigas, one of the world's largest freshwater fish, is considered an emerging species for aquaculture development in Brazil given its high growth rate and meat quality. However, the lack of reproductive control in captivity has limited the expansion of Arapaima farming. This study aimed to test the effects of hormonal induction using mGnRHa implants and size pairing on broodstock reproduction through the analyses of sex steroids. To do so, broodstock of different sizes (large, small or mixed) were paired and implanted. Plasma and cephalic secretion profiles of testosterone (T), 11-ketotestosterone (11-KT) and 17ß-oestradiol (E2) were analysed. Compared to control (non-implanted), implanted broodstock showed a significant increase in plasma 11-KT (large and small males) and T (large and mixed females) post GnRHa implantation. In females, a significant increase in plasma T levels was shown, however, E2 remained unchanged after implantation. Despite the lack of clear spawning induction, this study showed the potency of GnRHa on sex steroid production regardless of pairing groups. Interestingly, significant correlations between blood plasma and cephalic secretion levels of 11-KT in males and T in females were observed, indicating the possible release of pheromones through the cephalic canals of A. gigas.

Host Plant and Antibiotic Effects on Scent Bouquet Composition of Anastrepha ludens and Anastrepha obliqua Calling Males, Two Polyphagous Tephritid Pests.

In insects, the quality of sex pheromones plays a critical role in mating success and can be determined by the ability of larvae/adults to accrue chemical precursors. We tested the host-quality-effect hypothesis by analyzing the chemical composition of scent bouquets emitted by calling males of two polyphagous tephritid species (Anastrepha ludens and A. obliqua) that originated from 13 fruit species representing diverse plant families. In A. ludens, we worked with an ancestral host (Rutaceae), nine exotic ones (Rutaceae, Anacardiaceae, Rosaceae, Solanaceae, Lythraceae), and two species never attacked in nature but that represent candidates for host-range expansion (Solanaceae, Myrtaceae). In A. obliqua, we tested an ancestral, a native, and an exotic host (Anacardiaceae), one occasional (Myrtaceae), and one fruit never attacked in nature (Solanaceae). We identified a core scent bouquet and significant variation in the bouquet's composition depending on the fruit the larvae developed in. We also tested the possible microbial role on the scent bouquet by treating adults with antibiotics, finding a significant effect on quantity but not composition. We dwell on plasticity to partially explain our results and discuss the influence hosts could have on male competitiveness driven by variations in scent bouquet composition and how this could impact insect sterile technique programs.

An ant navigation model based on Weber's law.

We analyze an ant navigation model based on Weber's law, where the ants move across a pheromone landscape sensing the area using two antennae. The key parameter of the model is the angle [Formula: see text] representing the span of the ant's sensing area. We show that when [Formula: see text] ants are able to follow (straight) pheromone trails proving that for initial conditions close to the trail, there exists a Lyapunov function that ensures ant trajectories converge on and follow the pheromone trail, with these solutions being locally asymptotically stable. Furthermore, we indicate that the features of the ant trajectories such as convergence speed or oscillation wave length are controlled by the angle [Formula: see text]. For [Formula: see text], we present numerical evidence that indicates that ants are unable to follow pheromone trails. We also assess our model by comparing it to previous experimental results, showing that the solutions' behavior falls into biologically meaningful ranges. Our work provides solid mathematical support for experimental studies where it was found that ant perception follows a Weber's law, by proving that such models lead to the desired robust and stable trail following.

Diel Periodicity of 3-Methyl-2-Butenyl Butyrate Emissions by Bronze Bug Males Is Suppressed in the Presence of Females.

The bronze bug, Thaumastocoris peregrinus Carpintero & Dellapé (Heteroptera: Thaumastocoridae), is an exotic emerging pest in Eucalyptus commercial forests in South America, Africa, and southern Europe. Information on the chemical communication system and reproductive ecology of this insect is scant, and it may be relevant for designing management strategies for eucalypt plantations. Males emit large amounts of 3-methyl-2-butenyl butyrate, which attracts conspecific adult males but not females. To learn more about the biological function of this putative male-produced pheromone, we quantified this compound in volatile emissions collected from males, females, and couples, in three 4-h collecting periods during the morning, afternoon, and night of a single 24-h cycle. Our results showed that virgin males emit 3-methyl-2-butenyl butyrate in a diel time pattern, with an almost sevenfold difference between the afternoon emission peak compared to morning or night hours. In addition, we show that in the presence of females, males emit the compound in the same amounts throughout the photocycle. While a definite function cannot yet be attributed to the emission of 3-methyl-2-butenyl butyrate by T. peregrinus males, our findings point to an intraspecific function, possibly one related to male-male competition.

Morphology of putative chemosensory setae in males of the spider genus Ariadna Audouin (Araneae, Synspermiata, Segestriidae)

Chemoreception in spiders plays an important role in prey detection, conspecific recognition and recognizing chemical cues in the environment. Sexually dimorphic structures often suggest a role in mating and there are not many papers describing sexual dimorphism in chemosensory setae in spiders. In this study, we present the first detailed morphological description of scopulate putative chemosensory setae in the palpal tarsi (cymbium) and in the distal segments of the legs of adult males of seven species of the spider genus Ariadna (Segestriidae) [A. araucana Grismado, A. boliviana Simon, A. corticola Lawrence, A. maxima (Nicolet), Ariadna sp. 1 (AUS), Ariadna sp. 2 (AFR-CONT), Ariadna sp. 3 (AFR-MAD)]. Our results show three different grouping configurations of five morphologically different types of scopulate setae (types a–e). This is the first detailed description of this type of setae on legs of a Synspermiata spider contributing to the knowledge of the morphology of different types of sensilla in this group of spiders. Our findings show that the scopulated setae of Ariadna do not seem to be homologous to the pseudoscopula of Mesothelae and Mygalomorphae. We also discuss how our findings relate to previous hypotheses of female sex pheromone detection and support during copulation.

Tools for detecting insect semiochemicals: a review.

Semiochemicals are chemical compounds that are released by many species as a means of intra- and interspecific communication. Insects have extremely advanced olfactory systems; indeed, they rely on smell when performing many of their main behaviors, such as oviposition, breeding, prey location, and defense. This characteristic of insects implies that semiochemicals could be used for various applications, including in agriculture, where they could be employed along with other tools to control pest insects. The aim of this review is to present the main techniques used and the state of the art in the detection of semiochemicals, focusing on pheromones. In addition to the traditional methods of identifying semiochemicals, such as gas chromatography coupled to a high-resolution detection mode (e.g., flame ionization (FID), electron capture (ECD), photoionization (PID), or mass spectrometry (MS)), other tools are addressed in this review, including sensors and biosensors. While these new technologies may be used under laboratory conditions to improve or complement technologies that are already being used, they are mainly intended for use as new agricultural tools for detecting and controlling pest insects in the field.

Temporal Response of Foragers and Guards of Two Stingless Bee Species to Cephalic Compounds of the Robber Bee Lestrimelitta niitkib (Ayala) (Hymenoptera, Apidae).

Lestrimelitta spp. are stingless bees that steal food and nesting materials from other highly social bees to survive. Though most of their victim species respond, either aggressively or submissively, to cephalic components of Lestrimelitta, little is known about if such response changes at some point during extended periods of exposure. Moreover, potential synergistic effects due to a mixture of victim's alarm/defense pheromones and Lestrimelitta mandibular pheromones, like in an actual attack, have not been examined so far. In this paper, we investigated the response of two species of non-robber stingless bees, Scaptotrigona mexicana (Guérin) and Tetragonisca angustula (Latreille), to (a) cephalic compounds from crushed heads of nestmates, (b) cephalic compounds of Lestrimelitta niitkib (Ayala), and (c) a mixture of (a) and (b). We found that even though T. angustula did not react to nestmates' crushed head, its response towards L. niitkib cephalic compounds was stronger and lasted longer than that of S. mexicana. Interestingly, the addition of crushed heads of the non-robber species to L. niitkib crushed heads caused no significant increase in the alarm response of both species. It may be that the absence of an alarm pheromone in T. angustula made this species more receptive to extraneous odors, which is not the case for S. mexicana; however, more species must be studied to elucidate any pattern regarding the absence/presence of alarm pheromones and the corresponding response to intruders' pheromones.