Allen M. Young

Nonfloral sources of chemicals that attract male euglossine bees (Apidae: Euglossini).

We present chemical analysis of four rotten or fungus-infected logs that attracted fragrance-collecting male euglossine bees. Eight of the 10 volatile compounds detected have never been found in the fragrances of orchids pollinated by male euglossine bees. Nonfloral sources of chemicals such as rotting wood may constitute an important fragrance resource for male bees. Since rotten logs produce large quantities of chemicals over long periods of time, such nonfloral sources might be more important than flowers as a source of certain fragrances for some euglossine bee species. Fragrance collecting in euglossine bees might have evolved originally in relation with rotting wood rather than flowers.

Function of glandular secretions in fragrance collection by male euglossine bees (Apidae: Euglossini).

MaleEulaema cingulata (Fabricius) (Apidae: Euglossini) possess large cephalic labial glands that secrete a mixture of lipids. In the process of fragrance collection, males secrete the labial gland lipids onto the substrate. The mixture of lipids and fragrances is then taken up by the front tarsal brushes and transferred to the hind tibial organs. The labial gland secretions apparently serve as a nonpolar solvent and carrier that increases the efficiency of fragrance collection.

Habitat and Seasonal Relationships of Some Cicadas (Homoptera: Cicadidae) in Central Costa Rica

The peak emergence periods and habitats of cicadas (Homoptera: Cicadidae) were examined in the central highlands of Costa Rica for several years. The region included remnants of primary forest along streams, various types of secondary habitats, and had a 4-month dry season. If cicada species have similar ecological requirements, it was predicted that some species would occupy different habitats and others would have allochronic peak emergence periods, perhaps synchronized with the wet and dry season cycle. Of the five species occurring here three {Fidicina pronoe (Walker) F. amoena Distant and Conibosa sp.) occupy secondary habitats including mixed plantings of coffee and bananas, while Quesada gigas (Olivier) and Zammara smaragdula Walker occupy forest remnants. The three secondary-forest species exhibit allochronic emergences: F. amoena emerges during the dry season, F. pronoe near the end of it and Conibosa in the wet season, Extensive censuses of nymphal casts of Q. gigas and Z. smaragdula along a stream revealed allochronic peak emergence periods, in the dry season for the former and in the wet season for the latter. Both cicadas emerge from the same patches of habitat, lending further support to the hypothesis that these species are ecologically similar. Because there is a relatively small amount of original forest cover remaining in this region today, some cicadas are adapting to secondary habitats. Habitat preferences in cicadas are probably determined, at least in part, by the feeding associations of nymphs with the root crowns of certain plants.

Pollination biology of Theobroma and Herrania (Sterculiaceae)—I. Floral Biology

Floral characteristics related to pollination were studied in four species of Theobroma and one species of Herrania (Sterculiaceae) in Costa Rica. Anthesis was complete in T. cacao, T. simiarum, T. speciosum, and T. mammosum at 0615 hr following an extended period of floral development throughout the night. Flowers of both T. cacao and Herrania cuatrecusana were fully open by dawn and pollen sacs dehisced throughout the morning hours. Stigma and style receptivity, assessed by hydrogen peroxide tests, were high throughout the morning and early afternoon in T. cacao. Bagged flowers resulted in no fruit-set. When petal ligules were experimentally removed there was no change in rates of flower abortion or total numbers of aborted flowers, tentatively suggesting that these structures play little or no role in attracting pollinators. Both Theobroma and Herrania flowers possess ultraviolet light reflectance/absorbance patterns which may play a role in pollinator attraction. Uptake of neutral red stain in T. cacao and T. simiarum showed scattered glandular activity on petals and sepals, perhaps indicating location of nectaries or other secretory organs. Conspicuous glandular trichomes on the ovary, on the lower third of the style, and in a conspicuous “basal ring” between petals and sepals (most pronounced and colorful in species other than T. cacao) may be sources of both floral attractant and reward.Differences in floral biology among Theobroma and Herrania species suggest divergence in pollination strategies. The data presented are discussed in terms of plant-pollinator specializations in the New World tropics.RésuméLes caractéristiques florales liées á la pollinisation ont été étudiées dans quatre espèces de Theobroma et une espèce de Herrania (Sterculiaceae) au Costa-Rica. L’anthèse était complète dans T. cacao, T. simiarum, T. speciosum et T. mammosum á 06.15 hr après une longue période de développement floral au cours de la nuit. Les fleurs de T. cacao et de Herrania étaient complètement déhiscentes á l’aube et les sacs de pollen se sont ouverts pendant toute la matinée. La réceptivité des stigmates et des styles mesurée par des tests d’hydrogène peroxyde était élevé pendant la matinée et en début de’après-midi pour T. cacao. Les fleurs ensachées n’ont pas produit de fruits. Quand les ligules des pétales ont été enlevées á titre d’expérience il ne s’est produit aucun changement dans le taux d’avortement ou le nombre total de fleurs avortées suggérant que ces structures n’influencent que peu ou pas l’attraction des polliniseurs. Les fleurs de Theobroma et de Herrania peuvent toutes deux réfléchir ou absorber la lumière ultraviolette, ce qui peut jouer un rôle dans l’attraction des polliniseurs. L’absorption de colorant rouge neutre a révélé une activité glandulaire diffuse des pétales et sépales, indiquant peut-etre la localisation de nectaires ou autres organes secréteurs. D’évidents trichomes glandularies sur l’ovaire á hauteur du tiers inférieur du style et un “anneau basel” bien visible entre les pétales et les sépales (très prononcés et colorés dans les espèces autres que T. cacao) sont peut-étre les sources de l’attraction florale et de récompense nourricière. Les différences de biologie florale entre les espèces Theobroma et Herrania suggèrent des différences dans les stratégies de pollinisation. Les données présentées sont discutées en termes de spécialisations des polliniseurs de plantes dans les tropiques du Nouveau Monde.

COMPARATIVE ANALYSIS OF STEAM DISTILLED FLORAL OILS OF CACAO CULTIVARS (Theobroma cacao L., Sterculiaceae) AND ATTRACTION OF FLYING INSECTS: IMPLICATIONS FOR A Theobroma POLLINATION SYNDROME

Steam-distilled floral fragrance oils from nine distinctive cultivars ofTheobroma cacao L. (Sterculiaceae) in Costa Rica were examined with GC-MS to determine whether or not major differences existed among these cultivars for volatile constituents comprising 50% or more of the samples. The cultivars selected for floral oil analyses were chosen to represent diverse cultivars having supposedly different genetic backgrounds and histories of artificial selection for agronomic purposes. Cluster analysis revealed two major groupings of cultivars: those with higher molecular weight dominant compounds, and those having lower molecular weight compounds. Additionally, one cultivar, Rim-100, selected from criollo or ancestral-type cacao in Mexico and resembling criollo in the appearance of flowers and fruits, formed an extreme group having the highest molecular weight profile for major volatile compounds. Based upon these analyses, bioassays using McPhail traps were performed in an abandoned cacao plantation in northeastern Costa Rica during rainy and dry seasons to determine the relative attraction of these oils to flying insects. Bioassays revealed that the Rim-100 cultivar attracted by far the greatest numbers of cacao-associated midges (Diptera: Ceratopogonidae and Cecidomyiidae), as well as stingless bees (Hymenoptera: Apidae: Meliponinae), suggesting that a floral fragrance having high-molecular-weight volatiles is more potent as an attractant to flying insects than floral oils having lower-molecular-weight compounds. It is suggested that Rim-100 more closely resembles an ancestral or wild-type cacao than the other cultivars examined, and therefore it is more effective in attracting opportunistic dipteran floral visitors and pollinators than other cultivars in plantation settings. Several of the major volatile compounds found in the floral oils ofT. cacao and other species ofTheobroma occur in mandibular and other exocrine glands in various bees, including stingless bees and halictids, known visitors ofTheobroma flowers. These compounds are particularly present in noncultivated species ofTheobroma and have much more noticeable fragrances than the seemingly scentless flowers of cultivatedT. cacao selected for agriculture. It is hypothesized that the floral attraction system of ancestral or wild (noncultivated)T. cacao and other species ofTheobroma may have evolved to attract certain bees as their principal pollinators in natural habitats in the Neotropics, with a floral reward hypothesized as being sociochemicals needed by bees for mating, foraging, territorial defense, etc. Because of the many generations of extensive selection by cloning for desired cultivars,T. cacao might have lost much of its original floral attraction system for bees, instead being pollinated opportunistically by dipterans in plantation habitats. This may help to explain why natural pollination in cultivatedT. cacao is generally very poor relative to observed levels of fruit-set in wild or noncultivated species ofTheobroma.

Chemistry and possible roles of cuticular alcohols of the larval atlas moth

Abstract 1. 1. Cuticular wax from abdominal tubercles of Attacus atlas (Lepidoptera; Saturniidae) is primarily composed of 1-triacontanol in combination with 1-hexadecanol, 1-heptadecanol, 1-nonadecanol and 1-dotriacontanol. 2. 2. Evidence for the roles of wax in water conservation and defense against predators and parasitoids, and the defensive behavior associated with an additional thoracic defensive secretion are discussed. 3. 3. 1-Triacontanol at 2.28 × 10 −8 M, but not larval was containing this compound at the same concentration, increased the number of leaves, and leaf and stem fresh and dry weight of Ailanthus altissima seedlings, a host-plant of the Atlas moth.

On the evolution of cicada X host-tree associations in Central America

An hypothesis tout court is proposed to account for the association of cicadas (Homoptera: Cicadidae) with large-sized trees of the family Leguminosae in both climax forest formations and forest remnants in Central America. Based upon extensive field studies of these insects in Costa Rica, final-instar nymphal skins of many genera and species of Neotropical cicadas appear to be aggregated annually around individual large legume trees in a broad range of habitats in Costa Rica, and much of the reproductive behavior of the adult insects is also centered around these trees. A series of testable subhypotheses are generated based largely upon the assumption that cicadas, primarily through egg-placement behavior and nymphal feeding behavior, have coevolved with legume trees in climax forest formations of Central America, and perhaps elsewhere in the Neotropical Region. The “root crowns” of such trees, with some exceptions, might be optimal feeding sites for cicada nymphs in tropical forests.

On the evolution of egg placement and gregariousness of caterpillars in the Lepidoptera

Drawing heavily upon natural history data from the Neotropical butterfly fauna, an attempt is made to develop a model, with testable hypotheses, to account for the evolution of egg-clustering and larval gregariousness. Given the high diversity of both plant and butterfly species in the American tropics, there is a higher incidence of egg-clustering there, including some species with aposematically-colored immature stages. Emphasis is placed on the need to examine both the physical (mechanical) toughness of larval food plants for larval feeding success, and the spatial structuring of food plant populations. It is argued that when food plant spatial patchiness is high, the breadth of local food plant species usage low, plant growth rates high, fed-upon structures tough, butterfly dispersal low, and reproductive potential low, egg-clustering evolves. Such ecological character states, coupled with the occurrence of food plant patches in large sizes relative to the nutritional and fecundity needs of the butterfly specialist on the species, select for egg-clustering to ensure survival of the butterfly population in that habitat. It is emphasized that the model proposed here requires considerable examination through field studies.

Development and characterization of 16 microsatellites for Hoffmann’s two-toed sloth, Choloepus hoffmanni

Hoffmann’s two-toed sloth (Choloepus hoffmanni) is an arboreal mammal found throughout the Neotropics. Due to its limited dispersal power and reliance on forested habitats, C. hoffmanni could serve as a model species for understanding the response of mammals to land cover change. To better understand sloth life history and their response to tropical forest fragmentation and loss, we developed and characterized 16 polymorphic microsatellite markers. We tested each locus with 16–23 C. hoffmanni individuals sampled in northeastern Costa Rica. The number of alleles per locus ranged from three to seven, while mean observed heterozygosity was 0.56 and ranged from 0.33 to 0.75. All loci met Hardy–Weinberg expectations and none of the loci exhibited significant linkage disequilibrium. The microsatellite markers developed herein will be used to investigate dispersal rates and gene flow among habitat patches in Costa Rica, as well as provide insights into the life history of two-toed sloths.

An evolutionary-ecological model of the evolution of migratory behavior in the Monarch Butterfly, and its absence in the Queen Butterfly

This paper presents a model that generates testable hypotheses concerning the evolution of long-range migratory behavior in the Monarch Butterfly,Danaus plexippus and the general absence of such behavior in a related form, the Queen,D. gilippus (Lepidoptera: Nymphalidae: Danainae). An attempt is made to reconstruct a probable transition within the Neotropical forest-dwelling danaines associated with woody Asclepiadaceae (and to a lesser extent, perhaps some Apocyanaceae) as larval food plants to a progenitor stock of the Monarch and Queen in more seasonal tropical regions, and eventually temperate regions, and associated with herbaceous asclepiads such asAsclepias. A basic premise of the proposed hypothetical model is that the colonization of secondary habitats in seasonal tropical regions of Central America preadapted both forms to an eventual colonization of the sub-temperate and temperate zone of North America. The assumed evolutionary diversification of the herbaceousAsclepias species in North America provided an evolutionary stepping stone for the expansion of these danaines into this region. Owing to strong selection arising from the co-association of the Monarch and Queen with the same species ofAsclepias in the subtropical region of North America, eventually there was selection for the colonization of the higher latitudes by the Monarch, whereAsclepias thrived. Being essentially a tropical insect, the Monarch evolved an obligatory long-range migratory behavior to allow colonization of the temperate zone annually, and necessitating the use of overwintering sites in Mexico and other places.