Aggregation Behavior in Spiderlings: a Strategy for Increasing Life Expectancy in Latrodectus geometricus (Araneae: Theridiidae)

Studies on the biology of Latrodectus geometricus are scarce, especially on the behavior and life expectancy of the species. In this study we investigated the importance of the aggregation behavior of juveniles on life expectancy and longevity of the species. Egg sacs were collected in the urban area of Dourados- MS and transferred to the laboratory. The spiderlings hatched were separated into two groups: spiderlings aggregated and isolated, kept in the presence of luminosity. The same tests were run with egg sacs deprived of luminosity. A calculation of entropy was performed for all cases. Individuals grouped held under light exposure showed 14.3 days of life expectancy and 46 maximum longevity and 14.8 days of life expectancy and 32 days of longevity when isolated. For individuals grouped and deprived of light life expectancy was 29.8 days and maximum longevity 85 days and 19.3 days of life expectancy and 26 days of maximum longevity when isolated. The entropy of individuals kept in the presence of light, when grouped was H=0.692 and when isolated H=0.377. For individuals deprived of light, the entropy was H = 0.628 when kept grouped and H = 0.143 when isolated. Therefore it is concluded that the aggregation behavior and luminosity influence the longevity and life expectancy of spiderlings. Cannibalism must be a strategy to acquire food reserves contributing to the survival of a small number of individuals

Morphological Differences between Reproductive and Non-reproductive Females in the Social Wasp Mischocyttarus consimilis Zikán (Hymenoptera: Vespidae)

Phenotypic divergence plays an important role in establishment of the reproductive division of labor among castes in social insects; however, little is known about this subject in independent-founding polistine wasps. In this study, we investigated morphological differences among foundresses from associative and solitary foundations, as well as among females produced in different phases of the colony cycle in Mischocyttarus consimilis Zikán. Our results showed that the alpha foundress had significantly greater body size than auxiliary foundresses, although it did not differ in size from solitary foundresses. In addition, the alpha foundress had greater ovarian development than their auxiliary and solitary foundresses. We also demonstrated that gynes were significantly larger than workers. These results therefore suggest that the phenotype of females emerging in colonies M. consimilis can vary with the progress of the colony cycle, and that body size and ovarian condition are closely linked to the function performed by the foundress

Do Odontomachus brunneus nestmates request for help and are taken care of when caught?

In social insects, situations can arise that threaten an individual or an entire colony. When the call for help goes out, different behavioral responses are elicited by signals emitted from nestmates. In ants, the response can be one of redemptive behavior by the worker receiving it. However, little is known about the evolution of this behavior and in which group of ants it manifests. Therefore, this study investigates whether workers of Odontomachus brunneus Patton can act as rescuers, able to detect and respond to calls for help from nestmates. Laboratory experiments were carried out in which the legs of ants were trapped by tape, simulating capture by a predator. Nearby were nestmates able to receive and respond to a request for help. Two experiments were performed: 1. Calls for help were made at different distances, in order to test the response latency. 2. Evaluation of whether rescuers would respond differently to calls for help from nestmates, non-nestmates of the same species, and ants of another species. Finally, evaluation was made of the behaviors of the rescuers when they responded to requests for help from nestmates and ants of another species. It could be concluded from the results that O. brunneus workers respond to signals emitted by workers who may have been captured by a potential predator, prompting the performance of behaviors related to rescue attempts. The signals involved appear to have an optimal range and are species-specific. When exposed to a capture situation, this species transmits audible signals by stridulation, so it is possible that this type of signal may be involved, in addition to chemical signaling

Evaluation of Insects that Exploit Temporary Protein Resources Emphasizing the Action of Ants (Hymenoptera, Formicidae) in a Neotropical Semi-deciduous Forest

The majority of the ants is opportunistic and generalist foragers, commonly feeding on vegetable secretions, seeds, and living or dead animal material. They may be present on any type of substrate even, occasionally on carcasses. This work, then, aimed to evaluate the action of insects, especially ants, in the exploitation of protein resources in forest environment. Monthly collections were made over a year and, in each collection, were made observations during 12 consecutive hours. To simulate exposure of protein resources we used three types of baits, sardines, beef liver and chicken. To evaluate the importance of ants on protein resources for each type of bait there was a control replica with physical barrier to prevent their access. The ants were observed on all baits throughout the collection period. In total, the baits were visited by 34 species of ants. The main genus of ants to visit the baits were: Pheidole, Crematogaster and Solenopsis. These results demonstrate that the presence of ants is important to ecological succession on temporary protein sources in forest environments interfering in the occurrence of other frequent groups in this type of resource, such as flies, for instance. The species that dominated the baits, when presents, were those that regardless of size and aggressiveness, presented mass recruitment and exploited the baits with large flow of individuals Although some species that exhibit certain characteristics can locate the baits faster and eventually dominate them at some point, depending on the ants species that co-occur, the results for the sequence of colonization can be modified

Temporal polyethism, life expectancy, and entropy of workers of the ant Ectatomma vizottoi Almeida, 1987 (Formicidae: Ectatomminae)

We investigated the changes in the behavioral repertoire over the course of life and determined the life expectancy and entropy of workers of the ant Ectatomma vizottoi. Newly emerged ants were individually marked with model airplane paint for observation of behaviors and determination of the age and life expectancy. Ants were divided into two groups: young and old workers. The 36 behaviors observed were divided into eight categories. Workers exhibit a clear division of tasks throughout their lives, with young workers performing more tasks inside the colony and old workers, outside, unlike species that have small colonies. This species also exhibits an intermediate life expectancy compared to workers of other species that are also intermediary in size. This supports the hypothesis of a relationship between size and maximum life expectancy, but it also suggests that other factors may also be acting in concert. Entropy value shows a high mortality rate during the first life intervals

Variation in Chemical Composition of Cuticular and Nonpolar Compounds of Venom of Apoica pallens and Polistes versicolor

Although cuticular hydrocarbons and venom are important to the evolutionary success of social behavior, studies that investigated these compounds in tropical social wasps are rare. Thus, the aim of this study was to compare the cuticular chemical composition and the nonpolar portion of venom of Apoica pallens, a swarm-founding wasp and Polistes versicolor an independent-founding wasp. Gas chromatography coupled to mass spectrometry (GC/MS) technique was used. In the samples of A. pallens, 66 compounds were identified on the cuticle and 87 in venom, 13 are unique of the cuticle and 26 of venom. In the samples of P. versicolor, 85 compounds were identified on the cuticle and 60 in venom, 10 are exclusive of the cuticle and 5 of venom. The results show that, although they present different foundation types and organize in colonies with significantly different population number, the variation in chain length of compounds is relatively similar. In addition, in both types of samples of both species, the most representative class of compounds in content and number are the branched alkanes, which are recognized as the most effective during interactions between nestmates. However, there is greater similarity in content of shared compounds between samples of cuticle and venom of A. pallens, suggesting that because it is a species that is organized in more populous colonies, it may have a more elaborate signaling system based on volatile compounds of venom

Opportunistic Strategies for Capture and Storage of Prey of Two Species of Social Wasps of the Genus Polybia Lepeletier (Vespidae, Polistinae, Epiponini)

The foraging activity in social wasps is complex behavior that involves the ability to locate and transport the resources necessary for the colony. The activity is opportunistic and generalist, sometimes adapting to the availability of the resources when the colonies are exposed to critical environmental conditions. The aim of this study was to evaluate the opportunistic behavior of two species of wasps of the genus Polybia for the capture and storage of prey in the form of flights of winged. Five colonies of Polybia occidentalis (Olivier) and two colonies of Polybia paulista (L.) were collected. Six of them contained stored winged of termites, and one contained winged of ants. The results indicated that these two species practice an opportunistic foraging strategy and are able to store large quantities of protein resources in their colonies

Effect of Magnetic Field on the Foraging Rhythm and Behavior of the Swarm-founding Paper Wasp Polybia paulista Ihering (hymenoptera: vespidae)

The geomagnetic field can be used by insects for navigation and orientation, through different magnetoreception mechanisms. Magnetic sensitivity is very well documented in honeybees, ants and termites, but few studies have examined this capability in social wasps. The present study analyzed the magnetic sensitivity of the paper wasp Polybia paulista. The wasps' behavior was analyzed in the normal geomagnetic field and in the presence of external magnetic fields generated by permanent magnets or by Helmholtz coils. The frequency of foraging flights was measured in both conditions, and also the behavior of the individuals on the nest surface was analyzed. The magnetic field from the permanent magnet produced an increase in the frequency of departing foraging flights, and also the wasps grouped together on the nest surface in front of the magnet. The electromagnetic field created by the Helmholtz coils also increased foraging flights, but individuals did not show grouping behavior. This Helmholtz electromagnetic field induced wasp workers to perform “learning flights”. These results show for the first time that Polybia paulista wasps are sensitive to magnetic fields, including it in the list of animal models to study magnetoreception and magnetic sensitivity

Morphology and Histochemistry of the Venom Apparatus in Different Castes of the Ant Ectatomma vizottoi (Formicidae: Ectatomminae)

The elimination of toxins via a venom gland by some ant species is a component of a larger mechanism for capturing prey and defense. The present study describes the morphology and histochemistry of the venom apparatus of different castes of the ant Ectatomma vizottoi Almeida, 1987. Morphologically, the venom apparatus of queens, gynes and workers of E. vizottoi are similar and composed of the sting apparatus and three distinct portions: two secretory portions (convoluted gland and secretory filament), and a storage portion (reservoir) - a hollow sting apparatus covered in the terminal portion of the reservoir by a sclerotized cuticle. The venom gland of E. vizottoi is longer in queens and gynes than in workers. Furthermore, the epithelium of the convoluted gland is taller in the glands of queens and gynes than in workers, which may be indicative of greater toxin synthesis, or may be related to different body sizes of the castes. The morphology and histology of the venom apparatus reflect those of a generalist, while the histochemical tests indicated that this structure has the same chemical content of lipids, proteins and polysaccharides among queens, gynes, and workers. Images obtained by confocal microscopy and scanning electronic microscopy reveal a muscle layer surrounding the reservoir that is interlaced with secretory filaments, which fixes, in a manner, the filaments in place. This musculature serves to eject stored venom, which likely leads to greater success in defense or foraging

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