Tradition without social learning: scent-mark-based communal roost formation in a Neotropical harvestman (Prionostemma sp.)

Most models of habitat selection assume that individual animals choose and either reuse or abandon sites based on a constant reassessment of site quality. When survival is a function of the presence of conspecifics, however, the benefits of returning to traditional sites may override resource assessment. Many animals form roosting aggregations at what appear to be traditional sites. At our study site in Nicaragua, the harvestman Prionostemma sp. forms diurnal roosting aggregations on a small subset of the available spiny palm trees. With respect to physical characteristics and microclimate, the spiny palms used by the harvestmen resembled a random sample of those available, yet the same subset of trees was used in two different years (2001, 2003). This suggests that the location of aggregation sites is traditional, not a product of habitat limitation. Individual harvestmen were not faithful to particular roost sites, however, which raises the question of how the tradition could be maintained over time. In this paper, we present evidence, derived from a series of small-scale field experiments, that the harvestmen mark roosting sites chemically and enter marked sites preferentially when searching for places to roost. We also show that the harvestmen are sensitive to changes in site quality (the presence of spines) but will continue to use degraded traditional sites when no intact spiny palms are nearby. This system provides an example of how animal traditions could be maintained over multiple generations without learning. Site-labeling can be viewed as an external form of social memory.     

'Pheromone-like' compounds in the cuticle of aquatic Chironomus larva

Chironomid midges are the most commonly found dipteran insects in all types of aquatic ecosystems. Cuticular extract was bio-assayed, and it exhibited enhanced attraction to the larvae. Therefore, it was subsequently analysed by gas chromatography-mass spectrometry. Two compounds were identified as farnesol and farnesene. Bioassay of farnesol indicated its attractive properties. The components present in the cuticular extract can, therefore, be considered as pheromone-like compounds.     

The importance of experience in the interpretation of conspecific chemical signals

Foraging bumblebees scent mark flowers with hydrocarbon secretions. Several studies have found these scent marks act as a repellent to bee foragers. This was thought to minimize the risk of visiting recently depleted flowers. Some studies, however, have found a reverse, attractive effect of scent marks left on flowers. Do bees mark flowers with different scents, or could the same scent be interpreted differently depending on the bees’ previous experience with reward levels in flowers? We use a simple experimental design to investigate if the scent marks can become attractive when bees forage on artificial flowers that remain rewarding upon the bees’ return after having depleted them. We contrast this with bees trained in the more natural scenario where revisits to recently emptied flowers are unrewarding. The bees’ association between scent mark and reward value was tested with flowers scent marked from the same source. We find that the bees’ experience with the level of reward determines how the scent mark is interpreted: the same scent can act as both an attractant and a repellent. How experience and learning influence the interpretation of the meaning of chemical signals deposited by animals for communication has rarely been investigated.     

Insecticide resistance may enhance the response to a host-plant volatile kairomone for the codling moth, <Emphasis Type="Italic">Cydia pomonella</Emphasis> (L.)

The behavioral and electroantennographic responses of Cydia pomonella (L.) to the ripe pear volatile ethyl (2E,4Z)-2,4-decadienoate (Et-E,Z-DD), were compared in insecticide-susceptible and -resistant populations originating from southern France. A dose–response relationship to this kairomonal attractant was established for antennal activity and did not reveal differences between susceptible and resistant strains. Conversely, males of the laboratory strains expressing metabolic [cytochrome P450-dependent mixed-function oxidases (mfo)] or physiological (kdr-type mutation of the sodium-channel gene) resistance mechanisms exhibited a significantly higher response to Et-E,Z-DD than those of the susceptible strain in a wind tunnel experiment. No response of the females to this kairomone could be obtained in our wind-tunnel conditions. In apple orchards, mfo-resistant male moths were captured at significantly higher rates in kairomone-baited traps than in traps baited with the sex pheromone of C. pomonella. Such a differential phenomenon was not verified for the kdr-resistant insects, which exhibited a similar response to both the sex pheromone and the kairomonal attractant in apple orchards. Considering the widespread distribution of metabolic resistance in European populations of C. pomonella and the enhanced behavioral response to Et-E,Z-DD in resistant moths, the development of control measures based on this kairomonal compound would be of great interest for the management of insecticide resistance in this species.     

Morphophysiological and Population Adaptations ofAjuga reptansL. at the Northern Boundary of Its Range

The results of comprehensive morphophysiological and population studies on Ajuga reptansL., a species of the nemoral floristic complex, at the northern boundary of its range (in the middle taiga subzone of the Komi Republic) are reviewed. Adaptations at the cell, organism, and biocenotic levels are revealed. The maintenance and survival of the species at the boundary of its range are provided for by its physiological plasticity, resistance to low temperatures, and multiple variants of ontogeny. Prognosis of Ajuga reptansfuture status under conditions of global climate change and expansion of anthropogenically disturbed areas is favorable.     

Ontogeny and Population: Developmental Stability and Population Variation

By definition, the ontogenetic and population organization levels are fundamentally different. Studies at these levels are traditionally independent. However, it becomes increasingly evident that special analysis of individuals in terms of ontogeny is necessary for correct estimation of populations and their spatiotemporal dynamics, as well as for understanding the mechanisms of population processes.     

Development of sol–gel formulations for slow release of pheromones

A new type of dispenser for slow-release of sex pheromones and other semiochemicals was developed based on sol–gel polymers that can be useful for monitoring, mass trapping, and mating disruption in integrated pest management (IPM). Sol–gel matrices exhibit glass characteristics and allow control of the degree of cross-linking during the polymerization process in order to provide an optimal release rate for a particular pheromone. The advantages of sol–gel (silica) matrixes include keeping the added molecules chemically stable and enabling the sol–gel material to be applied in any desired thickness and pheromone quantity, and thereby readily modify release rates. In addition, sol–gels are primarily silica and water that are common in the environment and therefore safe for field dispensing. We developed a method for the entrapment of pheromones in sol–gel matrices that allowed release at an almost constant rate over many days in the field. For example, 2.5 mg (E)-5-decenyl acetate pheromone of peach twig borer, Anarsia lineatella, entrapped in various sol–gel formulations released 14–45 μg/day for up to 28 days. The codling moth (Cydia pomonella) pheromone in sol–gels was used in field tests to capture more codling moth males than unbaited control traps. We describe how the method may be modified to entrap other types of pheromones by making sol–gels with different pore sizes.     

Experience counts: females favor multiply mated males over chemically endowed virgins in a moth (<Emphasis Type="Italic">Utetheisa ornatrix</Emphasis>)

Determining the factors that affect male mating success is essential to understanding how sexual selection operates, including explanations of the adaptive value of female preferences and how variation in male traits is maintained in a population. Although females may appear to choose males based on a single parameter, female mate choice is often a complex series of assessments of male quality that can only be revealed through manipulation of multiple male traits. In the moth Utetheisa ornatrix (Lepidoptera: Arctiidae), females have been shown to judge males primarily on their production of a courtship pheromone, hydroxydanaidal, derived from defensive chemicals acquired as larvae. Recent work, however, suggested that other factors, including prior mating experience by males, may also influence the outcome of precopulatory interactions with females. I ran mating trials with one female and two males to determine whether there were any differences in male mating success based on their prior exposure to females, mating experience, and time between matings. Previously mated males were favored over virgins when both males lacked the pheromone, but courting experience and mating interval did not explain these differences in male mating success. Furthermore, multiply mated males lacking the pheromone were favored over virgin males that produced the pheromone, thus reversing the commonly observed trend of female precopulatory bias towards males with higher levels of the pheromone. These results demonstrate that males with mating experience can secure copulations despite deficiencies in the pheromone, and I provide possible mechanisms and discuss their implications regarding sexual selection.     

The role of a scent beacon in the communication of food location by the stingless bee, Melipona panamica

Melipona panamica foragers can deposit a scent beacon that influences the orientation of foragers near a food source. In misdirection experiments, newcomers (bees from the same colony as trained foragers) consistently preferred the feeder at which trained foragers had fed (training feeder) over an identical feeder at which bees had never fed (control feeder) even when the training feeder was placed at a site where experienced foragers had never foraged. Through similar misdirection experiments, the effective radius of the scent beacon was determined to be greater than 6 and less than 12 m. Foragers may deposit this beacon during a sequence of departure behaviors performed at the feeder. Prior to leaving the feeder with a load of sugar solution, bees tended to perform the following sequence of behaviors: (1) spinning, (2) grooming, (3) abdomen dragging, (4) excreting anal droplets, and (5) producing sounds, although not all behaviors were performed prior to each departure or at all sucrose concentrations (0.5–2.5 m). As sucrose concentration increased, the number of newcomers significantly increased, and the number of experienced foragers producing sounds and spinning on the feeder increased. The exact source of the scent beacon remains a mystery. However, three important sources have been excluded. When choosing between identical paired feeders, foragers were not attracted to the feeders with (1) anal droplets, (2) extracts of sucrose solution at which foragers had fed, or (3) mandibular gland extracts. They were indifferent to the first two preparations and exhibited only typical alarm behavior towards the mandibular gland (MG) extract: they oriented towards the feeder with MG extract but consistently landed on the feeder with no MG extract. Other authors have suggested that Melipona foragers deposit anal droplets to attract recruits, however the frequency of anal droplet production and the mass of anal droplets produced by M. panamica foragers are negatively correlated with sucrose concentration. Thus the scent beacon is evidently not deposited with anal droplets, infused into the feeder solution, or produced by mandibular glands. Received: 2 September 1997 / Accepted after revision: 30 January 1998