Acute Toxicity and Sub-lethal Effects of the Essential Oil of Aristolochia trilobata and Its Major Constituents on Nasutitermes corniger (Termitidae: Nasutitermitinae)

Nasutitermes corniger (Motschulsky, 1855) (Termitidae: Nasutitermitinae) is an important pest in urban environments and bioinsecticides can be an alternative to its control. Here, we determined the toxicity and repellence of the essential oil (EO) prepared from stems of Aristolochia trilobata L. (Aristolochiaceae) and its major constituents on N. corniger. We also investigated behavioral changes of individuals exposed to limonene. The lethal dose required to kill 50% of N. corniger population (LD₅₀) of EO of A. trilobata was 2.44 μg mg^-1. Limonene was the most toxic compound to N. corniger followed by linalool (LD₅₀ = 1.02 and 1.29 μg mg^-1, respectively). In addition, all treatments presented median lethal time (LT₅₀) less than 11 h. A. trilobata EO and its constituents showed irritability activity, but only limonene repelled soldiers more than workers. The negative behaviors of N. corniger groups were higher in individuals treated with limonene. A. trilobata EO and its constituents, especially the limonene, are promising for the control of N. corniger due the high toxicity, repellence, and possible disturbance in the colonies.

Does Distance Among Colonies and Resource Availability Explain the Intercolonial Aggressiveness in Nasutitermes aff. coxipoensis?

Aggressive behaviour can ensure animal access to local resources. To reduce constant costs in the defence of territories, species could save energy with conflicts avoiding aggression with neighbour or in situations with abundance of resources. In the present study, we analysed the effect of distance among colonies and resource availability on the aggression level and responses to chemical cues of Nasutitermes aff. coxipoensis (Holmgren) (Termitidae: Nasutitermitinae). Manipulation of resource offer was conducted in the field, where nests with different distances were kept without addition of baits (control), with addition of three or 16 sugarcane baits/nest. After 3 months, aggressiveness, linear and Y-shaped trail-following bioassays were carried out with all pairwise combinations of colonies in each treatment. Our results showed that aggressive index of N. aff. coxipoensis was affected by the resource availability. However, individuals from colonies with 0 and 3 baits/nest showed a higher number of fighting with neighbours than those from non-neighbours colonies. Termite workers from colonies without baits (control) followed shorter distance in the linear trails compared to those from colonies with addition of baits. In all treatments, there was no preference of workers in relation to the choice of chemical cues from own or other colonies. The response of intercolonial aggressiveness in N. aff. coxipoensis seems to be resource-dependent. These results may contribute to the comprehension of the use of space by N. aff. coxipoensis and could be useful to explain patterns of termite co-occurrence at different spatial scales, from local (inside the nest-e.g. cohabitation of nests by inquilines) to regional (e.g. around the nest).

Lethal Effect and Behavioral Responses of Leaf-Cutting Ants to Essential Oil of Pogostemon cablin (Lamiaceae) and Its Nanoformulation

Leaf-cutting ants belonging to the genus Atta (Formicidae: Myrmicinae) are important pests in agricultural and forest environments. In the present study, we evaluated the formicidal activity of the essential oil of Pogostemon cablin and its nanoformulation on the leaf-cutting ants: Atta opaciceps (Borgmeier, 1939), Atta sexdens (Linnaeus, 1758), and Atta sexdens rubropilosa Forel, 1908. The nanoformulation was developed by magnetic stirring using polyoxyethylene (36%), pure ethanol (36%), essential oil of P. cablin (18%), and water (10%). Bioassays of acute toxicity by fumigation and behavioral bioassays in treated arenas, with and without choice, were performed. The essential oil of P. cablin and its nanoformulation demonstrated efficient insecticidal activity and irritability to ant species. The concentration required to kill 50% of workers varied from 1.06 to 2.10 μL L^-1, with a mean time to death of less than or equal to 42 h. The essential oil of P. cablin and its nanoformulation reduced the displacement and velocity speed of the workers of A. opaciceps and A. sexdens rubropilosa in totally treated arenas. In the bioassays with choices, the three species of ants walked less and at a greater speed on the treated side of arena. This work demonstrates the potential of the essential oil of P. cablin and its nanoformulation to the generation of new formicidal products.

Ants Associated with Turnera subulata (Turneraceae): Elaiosome Attraction, Seed Dispersion and Germination

Symbiosis between plants and ants include examples in which the plant provides shelter and/or food for ants that, in turn, act in the defense or in the dispersion of seeds from the host plant. Although traditionally referred as mutualistic, the results of these interactions may vary with the ecological context in which patterns are involved. A range of species have facultative association with Turnera subulata (Turneraceae). Here, using behavioral bioassays, we investigated the effects of the most frequent ant species associated with T. subulata (Brachymyrmex sp.1, Camponotus blandus (Smith), Dorymyrmex sp.1, Crematogaster obscurata Emery, and Solenopsis invicta Buren) in the dispersion of plant host seeds and in the number of seedlings around the associated ant nests. We also evaluated the effects of these ant species in the germination of T. subulata seeds, in the consumption of elaiosome, and in the attractiveness to elaiosome odor. Our results showed that the ant species associated with T. subulata presented variation in the attraction by the odor and in the rate of consumption of the elaiosomes. However, none of the ant species studied contributed significantly to the increase of seed germination and seedling growth. Our results suggest that the consumption of the elaiosome by ant species is not a determinant factor to the success of germination of T. subulata. However, such species could contribute indirectly to seed germination by carrying seeds to sites more fertile to germination. In general, our results help to elucidate the results of ecological interactions involving ants and plants.

The Role of Resource Density on Energy Allocation in the Neotropical Termite Nasutitermes aff. coxipoensis (Termitidae: Nasutitermitinae)

Organisms acquire energy from environment and must allocate it among different life traits (growth, maintenance and reproduction). Social insects must manage the energy allocation to various levels such as colony growth and caste functions. Here, we addressed the question of whether resource density affects the energy allocation to the number of individuals and caste functions as well as nest's growth rate in the Neotropical termite Nasutitermes aff. coxipoensis (Homgren) (Termitidae: Nasutitermitinae). In a manipulative field experiment, colonies of N. aff. coxipoensis, with known volume, were maintained in plots with three different resource's density (0.32, 0.64 and 1.92 baits/m²) over 3 months. After this period, the number of individuals as well as the caste identity and nest volume were measured. Surprisingly, our results showed that colonies reared in the extremes of resource's density (0.32 and 1.92 baits/m²) produced a higher number of individuals compared with colonies reared with intermediate resource density (0. 64 baits/m²). The mean number of workers increased linearly with resource density; however, the average number of immature was higher in colonies reared with 0.32 baits/m² compared with colonies reared with 0.64 and 1.92 baits/m². No significant differences of resource density were observed in the mean number of soldiers, worker/soldier ratio as well as in the nest's growth rate. In conclusion, the resource's density seems to play an important role in determining the investment of energy in the number of individuals and caste in N. aff. coxipoensis colonies.

The impact of edge effect on termite community (Blattodea: Isoptera) in fragments of Brazilian Atlantic Rainforest

Habitat fragmentation is considered to be one of the biggest threats to tropical ecosystem functioning. In this region, termites perform an important ecological role as decomposers and ecosystem engineers. In the present study, we tested whether termite community is negatively affected by edge effects on three fragments of Brazilian Atlantic Rainforest. Termite abundance and vegetation structure were sampled in 10 transects (15 × 2 m), while termite richness, activity, and soil litter biomass were measured in 16 quadrants (5 × 2 m) at forest edge and interior of each fragment. Habitat structure (i.e. number of tree, diameter at breast height and soil litter biomass) did not differ between forest edge and interior of fragments. Termite richness, abundance and activity were not affected by edge effect. However, differences were observed in the β diversity between forest edge and interior as well as in the fragments sampled. The β diversity partitioning indicates that species turnover is the determinant process of termite community composition under edge effect. Our results suggest that conservation strategies should be based on the selection of several distinct sites instead of few rich sites (e.g. nesting).

Óleos essenciais de plantas medicinais e aromáticas no controle do carrapato rhipicephalus microplus

O carrapato bovino Riphicephalus microplus (Acari: Ixodidae) constitui um dos grandes problemas enfrentado pelos pecuaristas de várias partes do mundo. No Brasil este ectoparasita causa grandes prejuízos à bovinocultura devido ao processo de hematofagia e pela transmissão de agentes patogênicos nos animais hospedeiros. Diante dessa situação os produtores normalmente aplicam carrapaticidas organossintéticos de forma indiscriminada. Este método normalmente resulta em: intoxicação dos animais e dos aplicadores, resíduos de carrapaticidas nos produtos de origem animal, resistência dos carrapatos aos carrapaticidas químicos e poluição ambiental. Uma alternativa para diminuir esses problemas é uso de biocarrapaticidas de origem botânica. Os pesticidas botânicos são produtos naturais derivados do metabolismo secundário das plantas. Esse metabolismo produz uma grande diversidade de compostos com ação carrapaticida que podem ser explorados através do uso de óleos essenciais ou como modelo para síntese de pesticidas sintéticos. A necessidade de métodos mais seguros, menos agressivos ao homem e ao meio ambiente, tem estimulado a busca de novos carrapaticidas a partir de produtos vegetais. Assim, acredita-se que o uso de óleos essenciais de plantas medicinais e aromáticas de uma forma isolada ou associada pode reduzir: a velocidade do desenvolvimento da resistência dos carrapatos aos carrapaticidas, os resíduos nos produtos de origem animal e a toxicidade para os animais, aplicadores e meio ambiente.

Morphometry of the midgut of Melipona quadrifasciata anthidioides (Lepeletier) (Hymenoptera: Apidae) during metamorphosis

In Hymenoptera, midgut changes begin in the last instar. At this stage, the larval epithelial digestive cells degenerate, leaving only the basal membrane and the regenerative cells which will develop into a new epithelium during the pupal stage and in the adult. Epithelium renewal is followed by changes in volume and shape of the midgut. Morphometric analysis of digestive cells and total midgut volume of Melipona quadrifasciata anthidioides (Lepeletier) were conducted to verify whether cell volume increase are sufficient to account for the total midgut volume increase that occurs during metamorphosis. An increase in midgut volume was verified in spite of the scarcity of cell proliferation found during metamorphosis. At the end of metamorphosis, the increase in cell volume was not sufficient to explain the increase in volume of the midgut, indicating that an increase in the number of digestive cells is apparently necessary. Nevertheless, the mechanism by which regenerative cells reconstitute the epithelium during metamorphosis remains unknown.

Trophic controls delaying foraging by termites: reasons for the ground being brown?

Why is the ground brown, when detritivores and decomposers have the numbers and ability to speed up the turnover of dark-coloured soil organic carbon? We consider this soil analogue to the 'green world' hypothesis measuring in the field how fast termites occupied cellulosic baits of varying quantity and quality and how predation risks by ants affect such encounters. Single baits with ants were occupied by termites later than triple baits without ants, implying that termites may spend longer searching for suitable food than feeding on it, thereby delaying decomposition rates of both chosen and neglected items. Because termites' feeding speeds up dissimilation of polymers by decomposers, such results may imply that bottom-up and top-down forces, ultimately, impair carbon processing and release from soil. We argue that the ground is brown partly because of delays imposed upon termites' use of resources by bottom-up and top-down forces.