Discrimination of mixtures of female sex pheromone components by male Trichoplusia ni (Hubner)

Pheromone mixture discrimination by male cabbage loopers, Trichoplusiani (Hübner), was assessed in a wind tunnel by responsedifferences to paired stimuli. They discriminate differencesbetween mixtures that contain three and all six of the pheromonecomponents that are emitted by virgin females. The ability todiscriminate between these two mixtures is perplexing becauseonly three antennal pheromone specialist neurons respond atnatural stimulus intensities. The cabbage looper also discriminatedbetween mixtures whose component ratios differed slightly fromthat of the female. There was some interaction between the stimulusintensity, the distance between the stimulus sources, and possiblythe extent of the perceptual difference. The mixtures of pheromonecomponents failed to enhance the amount of upwind flight responseover that of Z7–12:Ac alone. Other evidence argues thatthe instantaneous release of pheromone may exceed time-averagedmeasures.     

Hydrolysis of sex pheromone by antennal esterases of the cabbage looper, Trichoplusia ni

Esterases were isolated from chemosensory sensilla on the antennaeof Trichoplusia ni (Hübner). The disc gel electrophoreticpatterns of these esterases from males and females were similar;however, more bands were observed in the antennae than in 8other tissues examined. Most of the esterases detected in the100,000 g supernatant of the antennal preparation could be dissociatedfrom the 100,000 g membrane pellet. Esterases from both maleand female antennae hydrolyzed the sex attractant, (Z)-7-dodecen-l-olacetate, more rapidly than did the legs, fat body or Malpighiantubules. The enzymes primarily responsible for pheromone catabolismwere less sensitive to paraoxon, eserine and p-(hydroxymercuri)benzoatethan those hydrolyzing 1-napthyl acetate. This suggested thata major portion of the observed pheromone-hydrolytic activitywas due to acetylesterases. Measurement of pheromone hyrolysisin sections of disc gels that contained separated antennal orabdominal body wall esterases revealed 2 peaks of activity withboth tissues; however, the rate of pheromone hydrolysis by theabdominal esterases was slower than that of the antennae. Thesignificance of these findings is discussed in relation to thepossibility of antennal esterases having a functional role inthe olfactory process of males of T. ni.     

Temporal analysis of adaptation in moth (Trichoplusia ni) pheromone receptor neurons

Summary The temporal pattern of response in chemoreceptor neurons reflects both the temporal distribution of stimuli and the timing of signal transduction, action potential generation and propagation. Here we analyze the temporal characteristics of the responses elicited in pheromone receptor neurons by computer-controlled rectangular pulses of odorant. Extracellular recordings from the HS sensilla trichodea on the antenna of male Trichoplusia ni reveal the activity of two neurons: the A neuron, which responds to the major component of the female pheromone blend, (Z)7-dodecenyl acetate and the B neuron, which responds to (Z)7-dodecenol. B neurons were divided into two classes (HR, LR), based on the magnitude and temporal pattern of their response to (Z)7-dodecenol. Most A and HR B neurons responded to rectangular pulses of various durations (0.1–40 s) with an initial phasic burst (100 ms), followed by a slowly declining tonic component. At moderate and elevated pheromone doses, prolonged stimulation resulted in significant reductions in the tonic response levels (adaptation); stimuli of increasing duration effected greater adaptation. Most LR B neurons lacked a phasic response component and showed virtually no adaptation with prolonged stimulation. Pheromone receptor neurons may differ in both their spectral and temporal response properties which may provide the animal with additional sensory information for blend discrimination and spatial orientation in complex natural pheromone plumes. The potential functional value of adaptation in the moth pheromone communication system is discussed.Abbreviations Z7,12:AC (Z)7-dodecenyl acetate - Z7,12:OH (Z)7-dodecenol - HR High response - LR Low response - HS High sensitivity     

Skeleton and musculature of the head and thorax of Trichoplusia ni (Hubner), (Lepidoptera: Noctuidae)

The muscles of the head, neck and thorax of the adult cabbage looper Trichoplusia ni are described for the first time. They are compared to those of Choristoneura fumiferana, Manduca sexta, Smerinthus geminatus, Antheraea polyphemus, Sphinx convolvuli, Crymodes devastator, and Danaus plexippus.     

Modulatory effects of octopamine and serotonin on male sensitivity and periodicity of response to sex pheromone in the cabbage looper moth,Trichoplusia ni

The pheromone-mediated flight behavior of male cabbage looper moths in a sustained-flight tunnel and random activity exhibited during scotophase were observed after males were treated with octopamine or serotonin (5 hydroxytryptamine). Octopamine induced a hypersensitivity to the olfactory signal, resulting in a significant lowering of the pheromone dose that elicited peak levels of response. Octopamine, however, did not affect the circadian rhythmicity of response to pheromone. In contrast, serotonin disrupted the circadian rhythmicity of response, resulting in a high percentage of males exhibiting random activity and response to pheromone throughout the entire 8 h scotophase instead of during the normal peak period during the latter part of the scotophase. Serotonin did not effect a decrease in the dose of pheromone eliciting peak response. In addition, at the highest dosages tested octopamine and serotonin induced opposite postures associated with a paralysis that occurred when males attempted to take flight to the pheromone.     

Neurophysiological responses of pheromone-sensitive receptor neurons on the antenna of Trichoplusia ni (Hubner) to pulsed and continuous stimulation regimens

Both the frequency and the temporal pattern of action potentialproduction in an insect olfactory receptor neuron are stronglyaffected by odorant composition and the time course over whichstimulus concentration varies. To investigate the temporal characteristicsof the neurophysiological responses of these neurons, we deviseda stimulus delivery system that allows us to repeatedly presentwell-mixed, constant concentration odor pulses with relativelysharp onsets and offsets. Here we compare neurophysiologicalresponses to several different stimulation regimens, includingpulses of different durations and repetition rates. During stimulationwith high concentrations of pheromone, the temporal patternof neural activity from olfactory receptor neurons on the antennaof Trichoplusia ni (Hübner) is characterized by an initialphasic period (100–200 ms), followed by a tonic periodwhich is typically maintained for the remaining duration ofthe stimulus. Different olfactory receptor neurons appear tovary among themselves in the relative distribution between thephasic and tonic portions of the overall discharge. During stimulationregimens involving rapid repeated pulses of odorants, a portionof the phasic response levels is preserved during each pulse.Consequently, T. ni males probably detect much of the fluctuationin concentration of pheromone that may normally occur downwindfrom the site of pheromone release.     

Response of both sexes of Trichoplusia ni (Lepidoptera: Noctuidae) to virgin females and to synthetic pheromone

Abstract. 1. Male and female Trichoplusia ni were caught at three locations in California in 1974 and 1975, in traps baited with virgin female T. ni or with synthetic female pheromone.
2. 71% of the females were captured between 20.00 and 21.00 hours; only 22% of the males.
3. Both mated and unmated females were trapped.
4. Comparisons of live trap vs. dead trap catches suggest that females are responding to the virgin females (or synthetic pheromone) and not to a combination of stimuli from the first trapped males plus female pheromone.     

Genetic variation in fitness parameters associated with resistance to Bacillus thuringiensis in male and female Trichoplusia ni

Resistance of insects to insecticides is often associated with reduced fitness in the absence of selection. We examined fitness trade-offs associated with resistance to the microbial insecticide, Bacillus thuringiensis (Bt), across full-sib families in a resistant population of Trichoplusia ni. Significant genetic variation in and heritability of susceptibility to Bt occurred among the full-sib families. Male pupal weight was positively correlated with Bt susceptibility, indicating a potential fitness cost, but no such correlation occurred for females. Significant heritability for pupal weight was present for males but not females. A significant negative genetic correlation existed between development time and Bt susceptibility, indicating that resistant larvae developed more slowly than susceptible larvae. Selection for Bt resistance in T. ni resulted in changes in life-history traits that affected males more than females.     

Plant exudates trigger leaf-trenching by cabbage loopers, Trichoplusia ni (Noctuidae)

Cabbage loopers, Trichoplusia ni, cut a narrow trench across leaves of plants that release exudate, then feed distal to the trench in an area of reduced exudation. The larvae do not normally trench plant species such as plantain, Plantago lanceolata, that lack exudate. To determine what cues elicit trenching, I reared larvae to the final instar on plantain, then applied test solutions to their mouthparts during feeding. Loopers that received latex from Lactuca serriola (Asteraceae) or phloem exudate from watermelon, Citrullus vulgaris (Cucurbitaceae), often responded by cutting a trench in plantain, even though these larvae had not previously encountered exudate nor previously trenched. Loopers that were allowed to trench and feed on L. serriola for 1 day prior to the assay subsequently cut trenches in plantain more frequently and in response to more fluids, including a viscous solution of polyethylene glycol and latex from a non-host, poinsettia (Euphorbia pulcherrima). Subsequent bioassays with larvae reared entirely on plantain tested whether bitter cucurbitacins or gelation are essential cues for trenching. Sap from non-bitter cucumber plants (Cucumis sativus) caused larvae to trench, showing that cucurbitacins are not required to induce trenching. Loopers also trenched after receiving cucumber sap that did not gel due to the addition of mercaptoethanol. An extract of sap lacking the proteins that cause gelation likewise triggered trenching. Further fractionation revealed that cucumber sap and also butternut squash sap (Cucurbita moschata) contain trenching stimulants that are small (molecular weight < 3,000) water-soluble molecules. Received: 13 January 1997 / Accepted: 6 June 1997     

Host-plant effects the expression of resistance to Bacillus thuringiensis kurstaki in Trichoplusia ni (Hubner): an important factor in resistance evolution

Pathogens are thought to exert strong selection on their hosts leading to increased host resistance. Bacillus thuringiensis kurstaki (Bkt) is a ubiquitous entomopathogen that has become the mainstay of nonchemical control of Lepidopteran pests and thus, the potential exists for the evolution of resistance in targeted host insects. We have studied the expression of Btk resistance in the cabbage looper, Trichoplusia ni (Hubner). For this generalist insect herbivore, three common host plants, tomato, pepper and cucumber, vary in suitability for larval growth and development. Here we show that the host plant also affects the overall toxicity of Btk, the relative expression of resistance between a resistant and a susceptible line and their F(1) reciprocal crosses, and importantly, the dominance of the resistance trait. This study demonstrates that tri-trophic interactions involving an insect, host plants and a pathogen have the potential to strongly influence the evolutionary response of an insect host to a pathogen.     

Antennal neurones specific for redundant pheromone components in normal and mutant Trichoplusia ni males

Abstract Recordings were made from the pheromone-sensitive receptor cells within antennal hairs of normal and mutant male cabbage loopers, Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae), using a cut-sensillum technique. From sampling 136 sensilla on normal males and 123 on mutant males, cells excited by pairs of behaviourally redundant minor pheromone components were discovered: Z9–14: Ac was found to be replaceable with 12: Ac and 11–12: Ac was found to be replaceable with Z5–12: Ac. These cells were not found during previous neurophysiological investigations, but explain most of the associations between mutually replaceable (redundant) pheromone components which had been demonstrated previously to be behaviourally redundant in wind tunnel studies. Our results indicate that the mutant gene in T.ni that affects pheromone production does not affect pheromone receptors in males. Using both AC- and DC-coupled recordings from receptor cells, we found that a single minor component could apparently hyperpolarize one cell while depolarizing another cell within the same sensillum, suggesting that noise reduction and other complex signal processing by receptor cells may contribute to odour processing in the macroglomerulus of the antennal lobe.     

Impact of (Z)-7-dodecenol and turbulence on pheromone-mediated flight manoeuvres of male Trichoplusia ni

Abstract. Turbulence and chemical noise are two factors which may influence pheromone-mediated flight manoeuvres of a moth in natural habitats. In this study, the effects of turbulence and the behavioural antagonist (Z)-7-dodecenol on flight manoeuvres of male Trichoplusia ni (Hübner) were evaluated in a wind tunnel. Male moths increase airspeed and course angles when turbulence is increased. This leads to significant increases in the length of flight tracks, but significant reductions in the time taken to reach a pheromone source. In less disturbed pheromone plumes, distributions of course angles and track angles of male T.ni show a prominent peak centred about 0° relative to the upwind direction, indicating that moths can temporarily steer directly upwind toward a pheromone source.
When (Z)-7-dodecenol is released 10 cm upwind of a pheromone source to form an overlapping plume downwind, course angles, airspeeds and ground-speeds of male T.ni are reduced significantly compared with those in uncon-taminated pheromone plumes. This results in a longer flight time to reach a pheromone source. The decrease in flight speed would decrease the rate of contact with filaments, and thereby perhaps allow the moth to detect uncon-taminated pheromone filaments independently from filaments containing the behavioural antagonist.     

Quantitative analysis of male responses released by female sex pheromone in Periplaneta Americana

Serial dilutions of purified female extracts of sex pheromone were analysed for their activity in releasing courting behaviour in males. Running activity and courting displays by males increased with the higher concentrations of sex pheromone. Males responded to sex pheromone in three distinct levels: arousal, running and courting displays. Individual male responses to equal dilutions were variable in that certain males had higher thresholds and required higher concentrations to initiate similar responses. Each level, respectively, was initiated by increasing concentrations of sex pheromone. When exposed to the highest concentration, there was a minimal temporal response time prior to the terminal courting displays. Secondarily purified extracts, as low as 4·5×10^?14 g, elicited a response from males.     

Induction of female sex pheromone production in male houseflies by ovary implants or 20-hydroxyecdysone

Implanting ovaries or injecting 20-hydroxyecdysone into male houseflies induced sex pheromone production, including (Z)-9-tricosene (muscalure), 9,10-epoxytricosane and (Z)-14-tricosen-10-one, which normally occurs only in vitellogenic females. Control males did not produce detectable amounts of these compounds. Injection of 20-hydroxyecdysone (5 μg/insect per day) for 3 days resulted in the accumulation of 1.81 μg/insect of (Z)-9-tricosene, 0.97 μg/insect of 9,10-epoxytricosane and 0.12 μg/insect (Z)-14-tricosen-10-one. Multiple injections of 20-hydroxyecdysone at doses as low as 50 ng resulted in the accumulation of 23:1, C₂₃ epoxide and C₂₃ ketone; shifted the distribution of label within the alkenes from 27:1 to 23:1 and decreased the amount of label in the hydrocarbon fractions as alkenes. Structures of the C₂₃ alkene and epoxide produced by the males were verified by gas chromatography-mass spectrometry. Radioactivity from [1-¹⁴C] acetate was incorporated into the C₂₃ alkene, epoxide and ketone in male insects after ovaries were implanted or they were injected with 20-hydroxyecdysone. Synthesis of the C₂₃ pheromone components decreased rapidly within several days after the administration of 20-hydroxyecdysone ceased, indicating that the enzymes involved in sex pheromone production were not permanently induced by hormone treatment. Ecdysone was also effective in initianing pheromone production in males, whereas inokosterone and cholesterol were not effective. Data presented demonstrate that male houseflies possess the metabolic capability to produce the sex pheromone components, and this suggests that 20-hydroxyecdysone alters the production of cuticular hydrocarbons such that the C₂₃ sex pheromone components become major products.     

Novel very long-chain methyl-branched alcohols and their esters,and methyl-branched alkanes in pupae of the cabbage looper,Trichoplusia ni (Hubner)

Four homologous series of very long-chain methyl-branched alcohols were found in the internal lipids of cabbage looper, Trichoplusia ni, pupae both as free alcohols and as esters. These alcohols were identified based on mass spectra of their TMS and acetate derivatives, and on the Kovats Indices and mass spectra of the alkanes obatained by reduction of their bromide derivatives with LiAlH₄. The four homologous series (from C36 to C46) consisted of monomethyl-, two dimethyl- and a trimethyl-branched alcohol series. The major alcohols (with the corresponding alkanes in parentheses) were identified as 24-methyltetracontan-1-ol (17-methyltetracontane), 24,28-dimethyltetracontan-1-ol (13,17-dimethyltetracontane), 24,36-dimethyltetracontan-1-ol (5,17-dimethyltetracontane) and 24,28,36-trimethyltetracontan-1-ol (5,13,17-trimethyltetracontane). The minor components had an odd number of carbon atoms (C37, C39, C41 and C43) in the carbon chain and the methylalkanes formed from their reduction had methyl branches on the 18- and 14,18-positions. The methylalkanes found internally in pupae were similar to those previously reported in larval cuticular lipids (de Renobales and Blomquist, Insect Biochem. 13, 493–502, 1983). Additional novel methylalkanes identified were 2,X-dimethylalkanes, 5,15-dimethylhentriacontane, 5,23-dimethyltritriacontane, 5,17,23-trimethyltritriacontane and 5,15,23-trimethylpentatriacontane. The methyl branching positions of the major methyl-branched alcohols were different from those of the major methylalkanes.     

Responses of male aphids to the female sex pheromone in Megoura viciae Buckton

Oviparae of Megoura viciae Buckton release a sex pheromone from numerous plaques on their hind tibiae. Adult males react to this scent in a variety of ways: inactive males are aroused; males already walking orient to the odour source; and copulatory activity is increased. These responses are only evoked within a few centimetres of the stimulus source and decline rapidly as the stimulus is diluted. Male responsiveness to the pheromone is unchanging throughout the light phase (of LD 12 : 12), although they show a marked circadian locomotor rhythm. Their sensitivity develops early in adult life and thereafter remains high, decreasing only slightly before death. However, although very young adults will orient to a pheromone source, they do not show copulatory responses until they are sexually mature. Larval males neither respond to the pheromone nor possess the antennal receptors (secondary rhinaria) which are essential for the adult reaction. Mating, and attempted copulation with suitable objects (e.g. coloured beads), is dependent upon appropriate visual and tactile stimuli; it can occur in the absence of the pheromone but is enhanced by its presence. Habituation to the scent does not prevent copulation, and conversely, copulation does not affect subsequent responsiveness to the pheromone. Once copulation has begun the pheromone has no effect on the efficiency of insemination. Vigorous intergeneric responses to the pheromones of female M.viciae and Acyrthosiphon pisum Harris were observed.     

Protein expression during parasite redirection of host (Trichoplusia ni) biochemistry

Expression of proteins during normal egg and larval development of Trichoplusia ni was compared with that occurring in hosts stung as eggs by the parasitic wasp Chelonus sp. near curvimaculatus. Those stung hosts which produced a parasite (truly parasitized), precociously expressed proteins associated with larval-pupal metamorphosis, as did those stung hosts which did not contain a developing endoparasite (pseudoparasitized). No highly abundant, low-intermediate molecular weight hemolymph proteins were observed in truly or pseudoparasitized larvae which did not also occur at some point in the development of normal larvae. A low abundance, high molecular mass (160,000 Da) protein was observed in the hemolymph of truly parasitized larvae, but not of normal or pseudoparasitized larvae. The protein is glycosylated and very acidic (pI near 4.5). The data show that any parasitization proteins injected or induced by the ovipositing female parasite are in low abundance, in contrast to situations reported for parasitic wasps which sting hosts as larvae.     

Guidance of flying male moths by wind-borne sex pheromone

ABSTRACT. On passing from clean air into a homogeneous cloud of sex pheromone in a wind tunnel flying male Adoxophyes orana (F.v.R.) (Lepidoptera: Tortricidae) turned more or less upwind and reduced the time and distance between their switchings of track from one side of the wind line to the other. These responses became adapted under the constant pheromone stimulation in the cloud, thereby arresting upwind progress; but the adapted moths would now 'lock-on' to an added pheromone plume and advance upwind along it. Moths also locked-on to the border of a pheromone cloud, not by turning back on losing the scent as previously supposed but by initiating the above programme of small-amplitude, crosswind movements (reversing anemomenotaxis). The onset and cessation of the pheromone stimulus produced anemotactic responses that differed quantitatively within a continuum, not two distinct kinds of response as previously supposed. The behavioural mechanism whereby uniform permeation of an area with synthetic sex pheromone can prevent males from finding females is reconsidered.