We présent field experiments and analyses that test both the assumptions and the prédictions of a model that showed how the swarm raids of the army ant Eciton burchel l i might be selforganizing, i.e., based on hundreds of thousands of interactions among the foraging workers rather than a central administration or hierarchical control. We use circular mill experiments to show that the run ning velocity of the ants is a sigmoidal function of the strength of their trail pheromones and provide évidence that the swarm raid is structured by the inter action between outbound and inbound forager traffic mediated by the phero mones produced by both of thèse sets of ants. Inbound traffic is also affected by the distribution of prey, and hence, sites of prey capture alter the geometry of the raid. By manipulating the prey distributions for E. burchel l i swarms, we have made them raid in a form more typical of other army ant species. Such selforganization of raids based on an interaction between the ants and their environment has profound consé q uences for interprétations of the évolution of army ant species.

Larval insect herbivores feeding externally on leaves are vulnerable to numerous and varied enemies. Larvae of the Neotropical herbivore, Chelymorpha alternans (Chrysomelidae:Cassidinae), possess shields made of cast skins and feces, which can be aimed and waved at attacking enemies. Prior work with C. alternans feeding on Merremia umbellata (Convolvulaceae) showed that shields offered protection from generalist predators, and polar compounds were implicated. This study used a ubiquitous ant predator, Azteca lacrymosa, in field bioassays to determine the chemical constitution of the defense. We confirmed that intact shields do protect larvae and that methanol-water leaching significantly reduced shield effectiveness. Liquid chromatography-mass spectrometry (LC-MS) of the methanolic shield extract revealed two peaks at 20.18 min and 21.97 min, both with a molecular ion at m/z 593.4, and a strong UV absorption around 409 nm, suggesting a porphyrin-type compound. LC-MS analysis of a commercial standard confirmed pheophorbide a (Pha) identity. C. alternans shields contained more than 100 μg Pha per shield. Shields leached with methanol-water did not deter ants. Methanol-water-leached shields enhanced with 3 μg of Pha were more deterrent than larvae with solvent-leached shields, while those with 5 μg additional Pha provided slightly less deterrence than larvae with intact shields. Solvent-leached shields with 10 μg added Pha were comparable to intact shields, even though the Pha concentration was less than 10% of its natural concentration. Our findings are the first to assign an ecological role for a chlorophyll catabolite as a deterrent in an insect defense.

Foliar endophytic fungi live inside healthy plant leaves, and in some cases they confer herbivore resistance to the host. All previous studies of endophyte–herbivore interactions have occurred in temperate areas, and many use correlations rather than experiments. In Panama, Glomerella cingulata is a common endophyte species found in healthy leaves, and Chelymorpha alternans is a common herbivore on Merremia umbellata, a tropical vine. We manipulated the abundance of G. cingulata in the leaves of M. umbellata. We then assessed the effects of high and low endophyte densities on the food choice, development, and reproductive success of the leaf beetle, C. alternans. In ‘choice’ experiments, adult females with a history of feeding on wild plants showed no preference when offered food plants with high and low endophyte densities. Further, in ‘no‐choice’ experiments, C. alternans larvae that were fed high‐ or low‐density endophyte leaves did not differ in development or survivorship. However, when larvae fed on leaves with low endophyte densities became adults, they produced 80 percent more offspring. This suggests high endophyte levels in hosts can have a negative effect on herbivore fecundity. Further experiments are necessary to understand whether the reproductive effects are due to feeding on low‐density endophytes in the larval or adult stages, and whether changes in reproductive success are motivated by the adult's perception of food quality or by physiological constraint due to food quality.

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Larvae of the leaf beetle Eurypedus nigrosignatus Boheman carry fécula and cast skins on their dorsa forming a protective device, commonly called a fecal shield. Survival from egg to adult eclosión, natural enemies, and relation to its hostplant, Cordia curassavica (Jacq.) Roem. and Schult. (Boraginaceae) were assessed. Overall survival was 2%; eggs and fourth instars were less susceptible to enemies than were early larval stages and pupae. Prédation accounted for the low survival of larvae, whereas parasitism for a low success rate of pupae. Six different predators including three spiders (Arachnida), a pentatomid, a reduviid (Heteroptera), and an ant (Hymenoptera) were observed. Reared parasitoids included a chalcidid (Hymenoptera) and a tachinid (Diptera). The fecal shield increases in size throughout larval development; however, the shield of prepupal individuals is partially lost. Shield chemical content very closely reassambles that of a particular host plant. Although the lower terpenoid concentration (per weight) in shields decreases with larval development, bigger shields as a unit contain larger amounts. Adults spend the Panamanian dry season buried in the ground directly under host plants. Eurypedus nigrosignatus is under intense selective pressures in Central Panama. ResumenLas larvas del escarabajo Eurypedus nigrosignatus Boheman acumulan heces y mudas sobre su dorso formando un artefacto defensivo lllamado el manto fecal. La sobrevivencia desde la deposición de huevos hasta la eclosión de adultos, los enemigos naturales, y su relation con su planta hospedera Cordia curassavica (Jacq.) Roem. and Schult. (Boraginaceae) fue evaluada. La sobrevivencia total fue de 2%; los huevos y el cuarto estadio fueron menos susceptibles a los enemigos que los estadios larvales más jóvenes y las pupas. La depredación fue el principal factor en la sobrevivencia baja de las larvas, mientras que el parasitismo por el bajo rendimiento de las pupas. Se observaron seis depredadores diferentes incluyendo tres especies de arañas (Arachnida), un pentatomido, un reduvido (Heteroptera) y una especie de hormiga (Hymenoptera). Los parasitoides criados en el laboratorio incluyen un chalcido (Hymenoptera) y un taquínido (Diptera). El manto fecal aumento de tamaño a través del desarrollo larvario; sin embargo, el manto se pierde en los estados prepupales. El contenido químico de los mantos es muy similar al de plantas hospederas particulares. Aunque la concentración (por peso) de terpenoids en los mantos disminuye con el desarrollo larvario, los mantos más grandes como una unidad contienen cantidades más altas. Los adultos pasan la temporada seca panameña enterrados en el suelo alrededor de las raíces su planta hospedera. Eurypedus nigrosignatus está bajo presiones selectivas intensas en Panamá central.Many Cassidinae are free-living on exposed plant parts (Windsor et al. 1992). Due to their preference for apical foliage, their presence tends to be predictable, and their vulnerability to enemies high (Jeffries and Lawton 19...