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T C Baker

Publications and source records attributed to T C Baker.

14 recordsLinked to original sources
PubMed2002

Unusual pheromone receptor neuron responses in heliothine moth antennae derived from inter-species imaginal disc transplantation.

Single-cell electrophysiological recordings were obtained from olfactory receptor neurons housed in sensilla trichodea along the adult antennae arising from transplantation of the antennal imaginal discs between larval male Helicoverpa zea and Heliothis virescens. The olfactory receptor neurons from the majority of type C sensilla sampled on transplanted antennae displayed response characteristics consistent with those of the species that donated the antennae. However, some of the sensilla type C sampled in either transplant type contained olfactory receptor neurons that responded in a manner typical of the recipient species or other neurons that have not previously been found in the type C sensilla of either species. The single-cell data help to explain behavioral results showing that some transplant males do fly upwind to both species' pheromone blends, an outcome not expected based on known antennal sensory phenotypes. Our results suggest that host tissue can influence antennal olfactory receptor neuron development, and further that because of a common phylogenetic ancestry the donor tissue has the genetic capability to produce a variety of sensillar and receptor types.

Action Potentials↗
PubMed2002

Host plant volatiles synergize responses of sex pheromone-specific olfactory receptor neurons in male Helicoverpa zea.

Single-cell electrophysiological recordings were obtained from olfactory receptor neurons in antennal trichoid sensilla of male corn earworm, Helicoverpa zea. Spontaneous activity of the neuron specific for the major component ( Z)-11-hexadecenal, the conspecific female-emitted sex pheromone, was not affected by exposure to host plant volatiles. However, stimulations with binary mixtures of a threshold dosage of the pheromone component and increasing dosages of either linalool or ( Z)-3-hexenol significantly synergized the pheromone-specific neuron's firing rates compared with responses to the major pheromone component alone. Cross-adaptation studies confirmed that the enhanced impulses originated from the pheromone-component-tuned neuron. Because plant volatiles do not stimulate the pheromone-specific neuron when presented alone, the pheromone plus host odor blend would be interpreted as containing more pheromone than it actually does when processed by the pheromone-processing portion of the antennal lobe.

Action Potentials↗
PubMed2001

Odour-plume dynamics influence the brain's olfactory code.

The neural computations used to represent olfactory information in the brain have long been investigated. Recent studies in the insect antennal lobe suggest that precise temporal and/or spatial patterns of activity underlie the recognition and discrimination of different odours, and that these patterns may be strengthened by associative learning. It remains unknown, however, whether these activity patterns persist when odour intensity varies rapidly and unpredictably, as often occurs in nature. Here we show that with naturally intermittent odour stimulation, spike patterns recorded from moth antennal-lobe output neurons varied predictably with the fine-scale temporal dynamics and intensity of the odour. These data support the hypothesis that olfactory circuits compensate for contextual variations in the stimulus pattern with high temporal precision. The timing of output neuron activity is constantly modulated to reflect ongoing changes in stimulus intensity and dynamics that occur on a millisecond timescale.

Action Potentials↗
PubMed1998

Behavioral antagonism in the moth Helicoverpa zea in response to pheromone blends of three sympatric heliothine moth species is explained by one type of antennal neuron.

We have discovered a type of sensillum on the antennae of male corn earworm moths, Helicoverpa zea, that houses two types of receptor neuron (RN) that explains both the upwind flight attraction of males to their own species' pheromone blend and arrestment to the quite similar blends emitted by females of three other sympatric North American heliothine species. The first RN type is a large-spiking neuron that is most sensitive to (Z)-9-hexadecenal (Z9-16:Ald), the secondary H. zea pheromone component that along with the major component, (Z)-11-hexadecenal, causes attraction to the female. This RN is also responsive to (Z)-9-tetradecenal (Z9-14:Ald; not a H. zea pheromone component) at higher dosages. The sensitivity of this RN thus explains the attraction that has been observed in other studies when small proportions of Z9-14:Ald are added to Z11-16:Ald to mimic the conspecific blend. The second type of RN in this sensillum is a small-spiking neuron that is again responsive to Z9-14:Ald (which in larger proportions acts as a strong antagonist to upwind flight), but this RN is actually more sensitive to two other strong behavioral antagonists, (Z)-11-hexadecenyl acetate and (Z)-11-hexadecenol. Thus, activation of this single broadly tuned 'antagonist' RN could explain why H. zea males will orient only to their conspecific females. These three compounds are emitted by females of three other North American species, H. subflexa, H. phloxiphaga, and H. virescens, as agonists in their blends, which also contain the H. zea components Z11-16:Ald and Z9-16:Ald. This antagonist RN may also explain why a blend of Z11-16:Ald and a small amount of Z9-14:Ald is never as attractive to H. zea males as the conspecific blend. Enhanced specificity for the conspecific blend arises because the antagonist RN is never stimulated to fire, even when large proportions of the pheromone component, Z9-16:Ald, are added to Z11-16:Ald. When Z9-14:Ald is used instead of Z9-16:Ald, however, and the proportion of Z9-14:Ald becomes too great, the threshold of the antagonist neuron as well as that of the agonist neuron is exceeded, and the upwind flight response begins to be suppressed.

Aldehydes↗
PubMed1994

Reiterative responses to single strands of odor promote sustained upwind flight and odor source location by moths.

We characterized single upwind surges of flying male Heliothis virescens moths in response to individual strands of pheromone generated experimentally in a wind tunnel. We then showed how this surge functions in this species as a basic 13.4-cm, 0.38-sec-long building block that is strung together repeatedly during typical male upwind flight in a normal pheromone plume. The template for a single iteration, complete with crosswind casting both before and after the straighter upwind surging portion, was exhibited by males flying upwind to pheromone and experiencing filament contacts just frequently enough to produce successful upwind flight to the source, as hypothesized by an earlier model. Also as predicted, with more frequent filament contact by males, only the straightest upwind portions of the surges were reiterated, producing direct upwind flight with little crosswind casting. Electroantennogram recordings made from males in free flight upwind in a normal point source pheromone plume further support the idea that a high frequency of filaments encountered under the usual pheromone plume conditions promotes only these repeated straight surges. In-flight electroantennogram recordings also showed that when filament contacts cease, the casting, counterturning program begins to be expressed after a latency period of 0.30 sec. Together these results provide a plausible explanation for how male and female moths, and maybe other insects, fly successfully upwind in an odor plume and locate the source of odor, using a surging-casting, phasic-tonic response to the onset and disappearance of each odor strand.

Journal Article↗
PubMed1988

Adaptation of antennal neurons in moths is associated with cessation of pheromone-mediated upwind flight.

A wind-borne plume of sex pheromone from a female moth or a synthetic source has a fine, filamentous structure that creates steep and rapid fluctuations in concentration for a male moth flying up the plume's axis. The firing rates from single antennal neurons on Agrotis segetum antennae decreased to nearly zero within seconds after the antennae were placed in a pheromone plume 70 cm downwind of a high-concentration source known from previous studies to cause in-flight arrestment of upwind progress. In a separate experiment, the fluctuating output from chilled neurons on Grapholita molesta antennae became attenuated in response to repetitive, experimentally delivered pheromone pulses. The attenuation was correlated with a previously reported higher percentage of in-flight arrestment exhibited by moths flying at cooler compared to warmer temperatures. These results indicate that two peripheral processes related to excessive concentration, complete adaptation of antennal neurons, or merely the attenuation of fluctuations in burst frequency, are important determinants of when upwind progress by a moth flying in a pheromone plume stops and changes to station keeping. Also, adaptation and attenuation may affect the sensation of blend quality by preferentially affecting cells sensitive to the most abundant components in airborne pheromone blends.

Action Potentials↗
PubMed1988

Measured behavioural latency in response to sex-pheromone loss in the large silk moth Antheraea polyphemus.

Males of the giant silk moth Antheraea polyphemus Cramer (Lepidoptera: Saturniidae) were video-recorded in a sustained-flight wind tunnel in a constant plume of sex pheromone. The plume was experimentally truncated, and the moths, on losing pheromone stimulus, rapidly changed their behaviour from up-tunnel zig-zag flight to lateral casting flight. The latency of this change was in the range 300-500 ms. Video and computer analysis of flight tracks indicates that these moths effect this switch by increasing their course angle to the wind while decreasing their air speed. Combined with previous physiological and biochemical data concerning pheromone processing within this species, this behavioural study supports the argument that the temporal limit for this behavioural response latency is determined at the level of genetically coded kinetic processes located within the peripheral sensory hairs.

Animals↗
PubMed1976

Reinvestigation of oak leaf roller sex pheromone components and the hypothesis that they vary with diet.

The sex pheromone of the oak leaf roller, Archips semiferanus, was identified as a specific blend (67:33) of trans-11- and cis-11-tetradecenyl acetates. The pheromone blend of females from a semisynthetic diet and from three oak species did not vary significantly. Males from these diets responsded in the laboratory and the field only to treatments approximating the 67 : 33 blend. These findings conflict with the hypothesis that the composition and perception of month sex pheromones vary with slight changes in diet.

Animals↗