L-lactic acid: a human-signifying host cue for the anthropophilic mosquito Anopheles gambiae

Using a dual-choice olfactometer, the role of L-lactic acid was investigated in relation to host-seeking and selection by female Anopheles gambiae Giles sensu stricto (Diptera: Culicidae) mosquitoes in a Y-tube bioassay. L-lactic acid alone was not attractive, but it significantly augmented the attractiveness of CO2, skin odour and skin-rubbing extracts from humans and other vertebrates. Comparing the left and right index fingers of the same person, one could be made more attractive than the other by adding L-lactic acid to the air stream over that finger. The difference in L-lactic acid concentration between the two air streams offered to the mosquitoes fell within the natural range of variation emanating from a human hand, suggesting that L-lactic acid modulates intraspecific host selection by An. gambiae. Analysis of skin rubbings from various vertebrates (carnivores, chickens, primates, rodents, ungulates) indicated that humans have uniquely high levels of L-lactic acid on their skin. Tests with extracts of skin rubbings from cows and humans, with and without added L-lactic acid, suggest that naturally lower levels of L-lactic acid contribute to the lesser attractiveness of non-humans to An. gambiae s.s.     

Transfection of human endothelial cells with HIV-1 tat gene activates NF-kappa B and enhances monocyte adhesion

Human immunodeficiency virus (HIV)-1 Tat released from HIV-1-infected monocytes is believed to enter other cells via an integrin-facilitated pathway, resulting in altered gene expression. Indeed, exogenous Tat protein can increase cell adhesion molecule gene expression in human endothelial cells. Signaling pathways initiated by Tat in endothelial cells are not known. We evaluated the ability of endogenous tat to stimulate monocyte adhesion via activation of nuclear factor-kappaB (NF-kappaB) within human umbilical vein endothelial cells. Transfection with pcTat, but not control vector DNA, increased NF-kappaB binding activity, NF-kappaB luciferase reporter activity, and monocyte adhesion. pcTat also increased kappaB-dependent HIV-1-LTR-CAT reporter activity 28-fold compared with a 3-fold increase produced by transfection with an equivalent amount of pcTax (from human leukemia virus). The pcTat-induced increase in pNF-kappaB-Luc activity and monocyte adhesion to endothelial cells was blocked by cotransfection with dominant-negative mutant IkappaBalpha and by incubation with 10 mM aspirin. We conclude that monocyte adhesion to human endothelial cells stimulated by pcTat is mediated via an NF-kappaB-dependent mechanism. Furthermore, inhibition studies using aspirin suggest that pcTat-stimulated NF-kappaB activation and monocyte adhesion occur via a redox-sensitive mechanism.     

Antennal resolution of pulsed pheromone plumes in three moth species

Male antennae of Cadra cautella,Pectinophora gossypiella, and Spodoptera exigua were presented with 20-ms-duration pulses of their two-component pheromone at rates of 1 to 33 Hz. Fourier analyses of electroantennograms resolved the temporal structure of trains of pheromone filaments delivered at up to 33 Hz for C. cautella and S. exigua and 25 Hz for P. gossypiella. Pheromone components tested separately for each species were generally equivalent in filament resolution to complete blends. Ambient temperatures of 18, 23 and 28 °C affected filament resolution only slightly, with poorer ability to discriminate rapidly pulsed signals at 18 °C. The question of how, or indeed if, such frequencies are conserved beyond the peripheral nervous system, remains.     

Evidence for 1-(Malonylamino)cyclopropane-1-Carboxylic Acid Being the Major Conjugate of Aminocyclopropane-1-Carboxylic Acid in Tomato Fruit

Tomato (Lycopersicon esculentum Miller) fruit discs fed with [2,3-¹⁴C]1-aminocyclopropane-1-carboxylic acid (ACC) formed 1-malonyl-ACC (MACC) as the major conjugate of ACC in fruit throughout all ripening stages, from immature-green through the red-ripe stage. Another conjugate of ACC, γ-glutamyl-ACC (GACC), was formed only in mature-green fruit in an amount about 10% of that of MACC; conjugation of ACC into GACC was not detected in fruits at other ripening stages. No GACC formation was observed from etiolated mung bean (Vigna radiata [L.] Wilczek) hypocotyls, etiolated common vetch (Vicia sativum L.) epicotyls, or pea (Pisum sativum L.) root tips, etiolated epicotyls, and green stem tissue, where active conversion of ACC into MACC was observed. GACC was, however, formed in vitro in extracts from fruit of all ripening stages. GACC formation in an extract from red fruit at pH 7.15 was only about 3% of that at pH 8.0, the pH at which most assays were run. Our present in vivo data support the previous contention that MACC is the major conjugate of ACC in plant tissues, whereas GACC is a minor, if any, conjugate of ACC. Thus, our data do not support the proposal that GACC formation could be more important than MACC formation in tomato fruit.     

Flight Toward a Learned Odor and Factors Inducing Landing of Female Brachymeria intermedia (Hymenoptera: Chalcididae), a Parasitoid of the Gypsy Moth, Lymantria dispar (Lepidoptera: Lymantriidae)

Through a single oviposition experience in the presence of vanilla odor, female Brachymeria intermedia were conditioned to fly toward a source of vanilla odor in a wind tunnel. Conditioning was an associative process, and wasps were able to fly toward odor sources at much lower doses than the dose used in conditioning. Furthermore, upon approaching vanilla-scented paper rolls hung on a vertical cylinder, conditioned wasps landed on them readily, whereas few wasps landed on real pupae. However, more wasps reached pupae or pupal cases than white paper rolls. Visual and olfactory cues appeared to mediate the foraging behavior of wasps in conflicting ways. Therefore, the extent to which olfactory learning mediates foraging success in this species remains unresolved.     

COST OF REPRODUCTION IN POLEMONIUM VISCOSUM: PHENOTYPIC AND GENETIC APPROACHES

I measured the effect of early reproduction on subsequent growth and survival in the alpine perennial wildflower, Polemonium viscosum. Measurements were made over 4 yr on 34 maternal sibships under natural conditions. A significant phenotypic cost of early reproduction characterized the study population. Plants that flowered after only one year's growth had twice as many leaves and 25% more shoots than nonflowering individuals of equal age. However, early flowering decreased leaf number by 18% in the subsequent year and survivorship by 20% after two years relative to changes in leaf number and survival of nonflowering plants. For such trade-offs to shape the further evolution of reproductive schedules, flowering probability and those age-specific components of plant size that represent the energetic currency for reproductive costs must be heritable. Although families showed significant heterogeneity in the probability of early flowering, most (62%) entirely failed to flower. Moreover, phenotypic variation in vegetative size components at ages 1 and 2 had little genetic basis. Only at ages 3 and 4, after vegetative and demographic costs of early reproduction had been incurred, did vegetative size components (leaf length and number, and shoot number) vary significantly among families. Results of this study provide little evidence of a genetically based trade-off between early reproduction and subsequent survival in P. viscosum.     

Construction of genetically marked Vibrio cholerae O1 vaccine strains

Abstract Attenuated Vibrio cholerae O1 vaccine strains lacking the gene encoding the A subunit of cholera toxin have proven efficacious in preventing experimental cholera. As these strains move from closed, contained testing environment to large-scale field trials, a readily assayable phenotypic trait to distinguish a vaccine strain from wild-type V. cholerae O1 is desirable. We have constructed three derivatives of the attenuated V. cholerae strain CVD 103 which carry a mercury resistance or urease marker in the hlyA gene. CVD 103-HgR was constructed using a protracted marker-exchange procedure; this strain was found to have somewhat lowered colonisation efficiency in infant mice in comparison to its parent strain, CVD 103. The insertion of the resistance marker was repeated using a suicide vector system; CVD 103-HgR2 was found to colonise infant mice as efficiently as CVD 103. Strain CVD 103-UR, in which sequences encoding urease were inserted using a suicide vector, also colonised infant mice as well as CVD 103. The genetically marked strains CVD 103-HgR, CVD 103-HgR2 and CVD 103-UR form the basis for a generation of defined oral vaccines that may give single-dose, long-lasting protection to populations at risk from cholera.     

Carpels as leaves: meeting the carbon cost of reproduction in an alpine buttercup

We investigated the role of photosynthesis by reproductive organs in meeting the carbon costs of sexual reproduction in the snow-buttercup, Ranunculus adoneus. The exposed green carpels of snow-buttercup flowers have 1–2 stomata each. Net carbon assimilation rates of flowers are negative during bud expansion, but rise to zero at maturity, and become positive during early fruit growth. Experimental removal of separate whorls of flower parts demonstrated that the showy, nectary-housing petals account for most of the respiration cost of flower presentation. Conversely, photosynthesis by female organs contributes to a flower's carbon balance. Dipteran pollinators of R. adoneus are most active in sunny mid-morning to mid-afternoon intervals. At this time of day, rates of carpel photosynthesis (A_max) meet respiratory costs of pollinator attraction in fully expanded flowers. Achenes remain photosynthetically active until dispersal, and positive net carbon assimilation rates characterize infructescences throughout fruit maturation. Photosynthetic rates of achenes are positively correlated with infructescence growth rates. We tested the causal basis of this relationship by experimentally shading developing infructescences. Mature achenes from shaded infructescences were 16–18% smaller than those from unshaded controls. Leaf photosynthetic rates did not differ between plants bearing shaded and unshaded seed heads. Since female reproductive organs are only 8% more costly in terms of caloric investment than male ones and contribute to their own carbon balance, it is plausible that the energy cost of male function equals or exceeds that of female function in this hermaphroditic species.     

Effects of pheromone plume structure and visual stimuli on the pheromone-modulated upwind flight of male gypsy moths (Lymantria dispar) in a Forest (Lepidoptera: Lymantriidae)

The pheromone-modulated upwind flight ofLymantria dispar males responding to different pheromone plume structures and visual stimuli designed to mimic trees was video recorded in a forest. Males flying upwind along pheromone plumes of similar structure generated tracks that were similar in appearance and quantitatively similar in almost all parameters measured, regardless of the experimentally manipulated visual stimuli associated with the pheromone source. Net velocities, ground speeds, and airspeeds of males flying in point-source plumes were slower than those of males flying in the wider, more diffuse plumes issuing from a cylindrical baffle. The mean track angle of males flying in plumes issuing from a point source was greater (oriented more across the wind) than that of males flying in plumes issuing from a transparent cylindrical baffle. Males flying in point-source plumes also turned more frequently and had narrower tracks overall than males responding to plumes from a cylindrical baffle. These data suggest thatL. dispar males orienting to pheromone sources (i.e., calling females) associated with visible vertical cylinders (i.e., trees) use predominantly olfactory cues to locate the source and that the structure of the pheromone plume markedly affects the flight orientation and the resultant track.