Research

Do thrips serve as pollinators of the early-flowering manzanita plant?

Thrips are often considered pests, feeding primarily on flowers of economically important crops. However, thrips are quite common in natural habitats, and may serve ecological roles. We are currently looking at the role of thrips in pollinating a plant - pointleaf manzanit (Arctostaphylos pungens) whose flowering begins early in the season, when snow might still be found on the ground and conventional pollinators may not be very common. Thrips, however, are very common at that time. We conducted exclusion experiments to test the hypothesis that thrips pollinate manzanita, in addition to varifying thrips capacity to transfer pollen between plants.

Behavioral Defense Mechanisms in a Chemically-Protected Caterpillar

Swallowtail caterpillars of the species Battus philenor feed on Aristolochia plants, which are chemically-protected. The caterpillars sequester the chemicals and use them for their own protection from predators and parasitoids, both as larvae and as adults. In addition, caterpillars possess special evertible organs - osmeteria - between their head and thorax that emit volatile chemicals which repell predators. However, we found that there is a significant variation in the use of osmeteria in caterpillars. Contrary to our hypothesis that osmeteria would be used as a primary source of defense, many caterpillars used them in a limited manner, employing various behavioral defenses instead. We are planning to look at the underlying causes of this variation in osmeteria use in the caterpillars.

Click here for a poster on the topic presented at the Animal Behavior Society meeting in Boulder, CO (July 2013).

Synergy vs. Potency in Defense Secretions of True Bug Nymphs

One of the characteristics of true bugs (Heteroptera) is the presence of abdominal glands in the immature nymphal stages. These glands usually produce defense chemicals that vary among taxa, yet maintain levels of similarity in closely related groups. Learning about the compounds and their prevalence in different taxa can help shed light on the evolution of those chemical defenses. We found that within the infraorder Pentatomomorpha, the secretions of nymphs of the Pentatomid clade usually contain the hydrocarbon tridecane and a long chain keto-aldehyde as the most abundant components. Nymphs of the Coreioid and Lygaeoid clades contain little or no hydrocarbon, and a high prevalence of shorter chain keto-aldehydes. We hypothesized that the long chain keto-aldehyde would be less potent than its shorter homologs, and that bugs that carry the former would benefit from a synergistic effect of tridecane.

To test these hypotheses, we used three different behavioral assays using ants. We used predator-prey assay, where individual jumping ants (Harpegnathos saltator; thank you to the Liebig Lab at ASU) were served crickets treated with the different chemicals to test the deterring effect of the defensive compound; vapor experiment tested the effectiveness of the volatiles in paralyzing groups of the fire ant Solenopsis xyloni; a spray experiment tested the irritating effect of the chemicals on the ants Pogonomyrmex rugosus. The results show a synergistic effect of the combination of tridecane and the long chain keto-aldehyde in causing disturbance to predators and deterring them. The short chain keto-aldehydes were highly effective on their own.

Compounds that Correlate with Individual Reproductive Status in Social Insects

Reproductive division of labor in social insects is accompanied by the reliable communication of individual fertility status. A central question is whether there exists a general mechanism underlying this communication system across species. The best way to produce reliable information is through physiological markers tightly associated with reproductive status. Cuticular hydrocarbons exhibit this link to individual fertility in several species of ants, bees, and wasps, and we present the first evidence for such a system in non-Hymenoptera eusocial species.

Cuticular Hydrocarbons in Termites

In the termite Zootermopsis nevadensis, we identfied four polyunsaturated alkenes, which only occur in significant amounts on reproductives that are actively producing gametes. These compounds are either absent or only occur in small amounts in soldiers, worker-like larvae, and secondary reproductives with inactive gonads. In contrast to Hymenopteran social insects, both sexes express the reproductive peaks. the reproductive-specific hydrocarbons may promote tending behavior by worker-like larvae, or act as a primer pheromone, inhibiting the reproductive development of immature conspecifics.

Poison Gland Alkaloids and Cuticular Hydrocarbons in Fire Ants

In the red imported fire ant, Solenopsis invicta, both cuticular hydrocarbons and piperidine alkaloids from the poison glands correlate with the reproductive status of queens. Mature queens from monogyne and polygyne colonies possess higher proportion of cis-piperidines than immature queens. Mature queens, especially those from polygyne colonies, also possess more alkenes than immature queens.

Courtship Behavior of the German Cockroach

The male German cockroach performs a characteristic courtship behavior upon contacting a sexually receptive female: he turns away from the female and raises his wings, thereby exposing tergal glands whose secretions contain phagostimulatory substances. The female then mounts the male and feeds on these nuptial secretions; this behavior places her in the appropriate precopulatory position

Identification of Two Additional Components of the Female Contact Sex Pheromone

The multi component contact sex pheromone produced by females is responsible for eliciting courtship behavior. The most abundant components are 3,11-dimethylnonacosan-2-one and 3,11-diemethylheptacosan-2-one, which are oxidation products of 3,11-dimethylcosane and 3,11-dimethylheptane, respectively. The C29-dimethyl ketone is thought to be further metabolized to two less abundant pheromone components, 29-hydroxy-3,11-dimethylnonacosan-2-one and 29-oxo-3,11-dimethylnonacosan-2-one. Based on this

The Natural Stereoisomer of the Most Abundant Component of the Contact Sex Pheromone is the Least Effective at Eliciting Courtship Behavior

Using isolated male antenna dosed with synthetic test compounds to assay male behavior, we found that at high doses all four stereoisomers elicited responses from 100% of the males. However, at physiologically relevant doses similar to those found on the female antenna, the (3S,11S)-isomer was the least effective of the four stereoisomers at eliciting courtship responses in males. This is the first example of a natural stereoisomer having less bioactivity than related stereoisomers that do not occur naturally.

Males Court Nymphs!

We found that nymphs and their antennae also can elicit the full courtship response in adult males. We extracted lipids from the cuticular surface of nymphs and, guided by behavioral assays, we fractionated the extracts using various chromatography procedures. Mass spectrometry analysis of behaviorally active fractions revealed two classes of courtship-eliciting compounds: all nymphs possessed a novel, still unidentified compound that elicited courtship in adult males. In addition, in last instar females, we isolated four of the six adult female-specific contact sex pheromone components, consistent with differentiation of the sexes at this stage, and the onset of sexual maturation of the pheromone biosynthetic machinery. The results of our experiment with starved nymphs support the interpretation that nymphs engage in sexual mimicry to gain access to male-produced nuptial tergal secretions that are exposed and can be secured only during courtship.

Males Court Other Species!!

We found that contact with the antennae of 5 out of 20 assayed cockroach species elicited courtship behavior in German cockroach males. The heterospecific courtship-eliciting compounds were isolated by behaviourally-guided fractionation of the active crude extracts and compared to the native sex pheromone components. We identified two active compounds from the cuticular extract of the Oriental cockroach, Blatta orientalis - 11-methyl-heptacosan-2-one and 27-oxo-11-methylheptacosan-2-one; The former compound was confirmed by synthesis and proved to independently stimulate courtship in German cockroach males. There compounds share common features with, but are distinct from, any of the known contact sex pheromone components.

Identification of the Volatile Sex Pheromone of the Wide Wood Cockroach

The distribution of the endangered red-cockaded woodpecker, Picoides borealis, is now limited to pine forests of southeastern North America, where the endemic wood cockroach, Parcoblatta lata, is the most abundant of cockroach species. Not surprisingly, this species is the primary source of food for woodpecker nestlings, and monitoring its population could assist in evaluating habitat suitability for woodpecker conservation purposes. The female P. lata releases a long-range sex pheromone whose identification may be applied to monitor cockroach populations. The compound we identified is a macrocyclic lactone, which we named parcoblattalactone. We confirmed the structure by synthesis, and tested the synthetic pheromone in the field, where it effectively attracted P. lata males.

A song was written for this study by the sci-fi author Elissa Malcohn (to the tune of Walking in Winter Wonderland). Just in time for Christmas! Check it out! Also, the article was featured on ScienceDaily.

Regulation of Sex Pheromone Biosynthesis in the Cotton Bollworm

It was observed that females of the cotton bollworm, Helicoverpa armigera, are less receptive following copulation. A possible factor involved in this phenomenon is a male-produced peptide, called pheromonostatic peptide (PSP), which is transfered to females during copulation. A fragment of this peptide, isolated from a related species, H. zea, was synthesized and we tested its effect on the production of pheromone in females. We found that it inhibits the activity of PBAN - pheromone biosynthesis activating neurpeptide, and thus the production of pheromone is diminished. We also found that a common herbicide - diclofop - a known Acetyl-CoA carboxylase inhibitor, has a similar effect. This suggests that PBAN acts on this enzyme as well.