Dodecyl acetate,a second pheromone component of the cabbage looper moth,Trichoplusia ni

Dodecyl acetate was identified as a second component of the sex pheromone ofTrichoplusia ni (Hübner). Dodecyl acetate comprised 9.6% by weight of the total pheromone [(Z)-7-dodecenyl acetate plus dodecyl acetate] extracted from glands and 7.3% by weight of the total pheromone evaporated from the surfaces of glands. Dodecyl acetate appears to function as a short-range pheromone component. Evaporation at female release rates of a 1090 mixture of dodecyl acetate and (Z)-7-dodecenyl acetate in the field caused a significantly greater percentage of males to land on the pheromone source, increased significantly the time they spent on the source, but decreased significantly the time they spent searching for the source when within 50 cm, as compared to (Z)-7-dodecenyl acetate alone.Lepidoptera: Noctuidae.     

Pheromone-mediated responses of male cabbage looper moths,Trichoplusia ni,following various exposures to sex pheromone or (Z)-7-dodecenol

Prolonged preexposure (three days) of maleTrichoplusia ni to its six-component sex pheromone blend or its major pheromone component, (Z)-7-dodecenyl acetate, reduced subsequent upwind flight responses to a pheromone source. Preexposure to (Z)-7-dodecenol increased upwind flight responses to a pheromone source combined with (Z)-7-dodecenol. The impact of long-term preexposures was moderate when compared to the more immediate effects of background noise. When (Z)-7-dodecenyl acetate was presented as background noise, all maleT. ni failed to respond to a plume of the full pheromone blend. However, most moths succeeded in locking on to the pheromone plume and contacting the pheromone source in the presence of the five minor pheromone components as background noise. When (Z)-7-dodecenol was released as background noise the response rate to a pheromone source containing (Z)-7-dodecenol was increased dramatically. This indicates that males became adapted to (Z)-7-dodecenol while responding to the pheromone source. The results of this study indicate that both long-term preexposure treatments and immediate exposure to background noise can limit the ability of maleT. ni to respond to sex pheromone sources.     

Filamentous nature of pheromone plumes protects integrity of signal from background chemical noise in cabbage looper moth,Trichoplusia ni

(Z)-7-Dodecenol failed to interrupt pheromone-mediated anemotactic responses by male cabbage looper moths,Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae) in a wind tunnel when released 5 cm crosswind on both sides of the pheromone source or 10 cm upwind of the source to create an overlapping plume downwind. Significant inhibitory effects of (Z)-7-dodecenol were observed when released with the six-component pheromone blend from the same septum or abutting septa. These results indicate that (Z)-7-dodecenol needs to be received simultaneously with the pheromone blend to inhibit the anemotactic responses of males to the sex pheromone. We suggest that this feature and the filamentous nature of pheromone plumes render pheromone signals relatively protected from background chemical noise that may originate from pheromone plumes of other insect species. Unless filaments from a pheromone signal and an inhibitor arrive simultaneously, the integrity of the signal is maintained.     

Identification of male cabbage looper sex pheromone attractive to females

A multicomponent pheromone produced by male cabbage looper moths that is attractive to female moths in a flight tunnel bioassay was isolated and identified. Based on analyses of hairpencil extracts of male cabbage loopers and volatiles emitted by males, the pheromone has been identified as a blend consisting of (S)-(+)-linalool,p-cresol, andm-cresol. The chirality of the major component, (S)-(+)-linalool, is important for behavioral response of females. These pheromonal compounds were also identified as volatiles released by males when males were exposed to the principal pheromone component of female cabbage loopers, (Z)-7-dodecen-1-ol acetate. The amount of male pheromone released was increased significantly when males were exposed to a combination of (Z)-7-dodecen-1-ol acetate and the odor from cabbage. Neither linalool nor the cresols were detected in volatiles from cabbage or from males exposed to cabbage odor.     

Effects of host plant,Gossypium hirsutum L., on sexual attraction of cabbage looper moths,Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae)

Unmated female or male cabbage looper moths,Trichoplusia ni (Hübner), were attracted more often in a flight tunnel to a cage with moths of the opposite sex and a bouquet of cotton foliage. Increased sexual attractiveness of females with plants may be a result of stimulation of pheromone release in response to plant odor, since more males were attracted when odor of cotton foliage was passed over females than when odor of females was passed over cotton foliage before venting into the flight tunnel. Increased sexual attractiveness of males with plants is due in part to host odor enhancement of female attraction to male pheromone, since more females were attracted to synthetic male pheromone (a blend of enantiomers of linalool and isomers of cresol) and a cotton leaf extract than were attracted to male pheromone alone. A short synthesis procedure was developed for (S)-(+)-linalool, the major component of the male sex pheromone, isolated from hair pencils, used in these tests.     

Genetic aspects of interpopulational differences in pheromone blend of cabbage looper moth,Trichoplusia ni

The genetic basis of interpopulational differences in the pheromone blend emitted by the cabbage looper moth,Trichoplusia ni (Hübner), was examined by crossing individuals from a field-derived population (P₁) with individuals from a long-maintained laboratory colony (P₂). These colonies differed in the emission rate and relative proportions of four of the five known minor pheromone components, but not in the emission rate of the major component, (Z)-7-dodecenyl acetate (Z7-12Ac). These differences in pheromone blend were quantitatively small but biologically significant, because in the field, males responded preferentially to traps baited with a pheromone blend that is similar to that emitted by P₁ females relative to a blend similar to that emitted by P₂ females. In initial crosses, variation in the quantity and quality of pheromone blends among families of P₁, P₂, and F₁ hybrid females was examined. In F₁ females the relative proportions (quantity relative to the major component) of (Z)-5-dodecenyl acetate (Z5-12Ac) and (Z)-7-tetradecenyl acetate (Z7-14Ac) were intermediate to parental lines. In a second more extensive set of crosses, analyses included P₁, P₂, F₁, F₂, and selected backcrosses. The relative proportion of Z5-12Ac, Z7-14Ac, and Z9-14Ac emitted by F₁ females were intermediate to parental lines. The frequency distributions of relative proportions of these components emitted by females were not consistent with those expected under a single autosomal or sex-linked gene hypothesis, suggesting that more than one gene is involved in the quantitative differences in the pheromone blend.     

Comparison of electroantennograms from female and male cabbage looper moths (Trichoplusia ni) of different ages and for various pheromone concentrations

The electroantennogram (EAG) responses of both male and femaleTrichoplusia ni to two components of the female-released sex pheromone were determined over a range of concentrations of chemical and age of insect. The EAG was at a peak at a dose of 100 g for both dodecyl acetate and (Z)-7-dodecenyl acetate (Z7–12OAc) for both sexes. The EAG responses varied with age of the insect. Responsiveness to both components was at a maximum at three days postemergence for males followed by a fairly rapid senescence, and for females it peaked at three days followed by a rapid senescence forZ7–12OAc but not for dodcecyl acetate.     

Activity of perfluorobutyl-containing components in pheromone blend of cabbage looper moth,Trichoplusia ni

Substitution of nine hydrogens by nine fluorines in the butyl terminus of (Z)-7-dodecenyl acetate, the major component of the pheromone blend of the cabbage looper,Trichoplusia ni (Lepidoptera: Noctuidae), produces a highly volatile analog that is significantly less active as a replacement for the natural pheromone component, either alone or substituted in the sixcomponent pheromone blend of this species. When 9,9,10,10,11,11,12,12, 12-nonafluoro-(Z)-7-dodecenyl acetate (nf-Z7-12: OAc) was tested in a wind tunnel as a single component or as part of the six-component blend, males exhibited preflight activation, but they did not orient in the pheromone plume and fly upwind over a five-decade range of doses at levels comparable with those of the natural component and blend. Addition of large amounts of nf-Z7-12:OAc to the optimal dose of the natural blend also did not effect flight arrestment as when increased amounts of Z7-12:OAc were added. The nonafluoro (nf) analog of (Z)-9-tetradecenyl acetate, a minor component in theT. ni blend, did not affect male behavior when substituted in the sixcomponent blend, and substitution of both nf analogs in the natural blend produced the same results as observed for blends containing nf-Z7-12:OAc. The lack of an effect with substitution of nf-Z9-14:OAc is discussed in relation to the reported redundancy in the action of minor components inT. ni.     

Pheromone hydrolysis by cuticular and interior esterases of the antennae,legs, and wings of the cabbage looper moth,Trichoplusia ni (Hübner)

Examination was made of the hydrolytic activities of esterases obtained from the antennae, legs, and wings of 3-day-old cabbage looper moths,Trichoplusia ni (Hübner), by elution and by homogenation of those appendages. Pheromone hydrolysis in 1-min assays was monitored by use of tritium-labeled (Z)-7-dodecen-1-ol acetate and thin-layer chromatography to separate the reaction products. Listed according to the activities of the esterases obtained by homogenation, the organs were antennae > legs > wings. In contrast, the order according to the activities of the eluted esterases was wings > legs > antennae. Also, the eluted enzymes were less active than the esterases obtained by homogenization. The relatively high pheromone-hydrolyzing activity present in homogenized antennae suggests that the esterases originated inside the antennae and lends support to the hypothesis proposed in earlier investigations that pheromone-inactivating enzymes may play an important role in the olfactory process, possibly by clearing pheromone from the vicinity of the olfactory receptors. The esterases detected on the cuticle, on the other hand, may function by preventing surface accumulation of pheromone. The higher measured esterase activity in homogenates of prothoracic legs than of mesothoracic or metathoracic legs suggests that the prothoracic legs, which are used to clean the antennae of debris, may function by removing and degrading pheromone from the surface of antennae.Mention of a commercial or proprietary product does not constitute an endorsement by the USDA.     

A mutation in pheromonal communication system of cabbage looper moth,Trichoplusia ni

A mutation that results in a dramatic change in the relative proportions of the pheromone components produced by female cabbage looper moths has been found. The most notable changes involve reduction in the emission rate of the major component [(Z)-7-dodecenyl acetate], near absence of a component [(Z)-5-dodecenyl acetate] that is normally present at about 20% of the major component, and a remarkable ca. 20-fold increase in a trace component [(Z)-9-tetradecenyl acetate]. In spite of the multiplicity of changes in the pheromone blend, a genetic analysis indicates that the condition is controlled by a single autosomal gene. These mutants are ineffective in attracting conspecifics, but do attract another distantly related noctuid moth. These results suggest that the evolutionary process that leads to distinct chemical signals in sibling species may include single gene mutations that lead to major changes in the species-specific blend.     

Interpopulational variation in emitted pheromone blend of cabbage looper moth,Trichoplusia ni

Female cabbage looper moths,Trichoplusia ni, from laboratory colonies initiated from three locations across the United States emitted similar quantities and blend ratios of the six known pheromone components. In contrast, females from a long-established laboratory colony emitted a greater proportion of four of the five minor components relative to the major component, (Z)-7-dodecenyl acetate; only the relative proportion of 11-dodecenyl acetate was similar in all of the populations sampled. Females from this population emitted (Z)-7-dodecenyl acetate at a rate similar to that from females from field-collected colonies. Within each population there were highly significant correlations among the quantities of pheromone components of similar molecular weights. Correlations between components of different molecular weights were not as great, but often were significant. Similarities of blend ratios among field populations may indicate that the chemical signal in this species is conservative. The difference of the blend ratios in our laboratory population from the other populations may indicate a decrease in the intensity of selection pressure that usually would maintain these values.     

Behavioral and physiological responses of cabbage looper,Trichoplusia ni (Hübner), to steam distillates from resistant versus susceptible soybean plants

Soybean plant volatiles, extracted as steam distillates, significantly affected the behavior and biology of the cabbage looper,Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae). Distillates from the susceptible Davis variety attractedT. ni larvae and female adults, whereas those from resistant PI 227687 plants repelled them. When mixed in an artificial diet, steam distillates from PI 227687 plants caused mortality of first-instar larvae. Adults emerging from pupae topically treated with 5 g of such PI 227687 extractable showed developmental abnormalities. Larval feeding was significantly less on Davis leaves treated with PI 227687 volatiles as compared to solvent (acetone) or such Davis extractables. However, Davis volatiles on PI 227687 leaves did not increase larval feeding. HPLC analyses of steam distillates from susceptible Davis versus resistant PI 227687 indicated differences.     

Redundancy in a chemical signal: Behavioral responses of maleTrichoplusia ni to a 6-Component sex pheromone blend

The flight response of maleTrichoplusia ni was observed in a flight tunnel to a sex pheromone blend composed of six components:Z7–12Ac, 12Ac,Z5-12Ac, 11-12Ac,Z7-14Ac, and Z9-14Ac. The number of males reaching a 3000-g source of this blend was > 95%, equal to that observed to female glands and significantly greater than with the previously identified two-component blend (Z7-12Ac + 12Ac). In subtraction tests, all five-component blends, with the exception of the blend lacking the primary componentZ7-12Ac, and several four-component blends elicited similar peak levels of upwind flight, source contacts, and hairpencil displays to that observed with the six-component blend. We characterize the substitution of certain minor components for one another as a form of redundancy in the chemical signal and suggest that it contributes to response specificity and signal recognition in males. The results also support the concept that the full blend of components acts as a unit to influence male behavior at all phases of the response. Individual minor components were not responsible for eliciting specific behaviors in the sequence.     

Evolution of behavioral responses to sex pheromone in mutant laboratory colonies ofTrichoplusia ni

Male cabbage looper moths,Trichoplusia ni, from two colonies in which all females express an abnormal sex pheromone production phenotype were evaluated in a laboratory wind tunnel for upwind flight responses to the normal and abnormal sex pheromones. The abnormal sex pheromone blend consisted of 20 times as much (Z)-9-tetradecenyl acetate and 30-fold less (Z)-5-dodecenyl acetate compared to the normal pheromone blend. Initially, these males exhibited poor behavioral responses to the abnormal sex pheromone and maximum responses to the normal pheromone blend, indicating that there was no linkage between signal production and response. After 49 generations of laboratory rearing, males from the mutant colonies maintained good responses to the normal pheromone and increased their behavioral response to the abnormal sex pheromone to the same levels as for the normal pheromone. Over the same period, normal males maintained their preference for the normal pheromone. These results indicated that evolution had occurred in mutant colonies in favor of greater male responsiveness to the abnormal sex pheromone, resulting in the broadening of the response spectrum to pheromone blend ratios. This evolution presumably resulted from a mating advantage to those males that did not discriminate against mutant-type females in the mutant colonies.     

Behavioral responses of maleHeliothis zea moths in sustained-flight tunnel to combinations of 4 compounds identified from female sex pheromone gland

Each of the four compounds that have been identified from sex pheromone glands ofHeliothis zea female moths was examined for its ability to elicit sexual responses from male moths in a flight tunnel. Males flew upwind to (Z)-11-hexadecenal alone, but greater levels of behavioral activity were evoked with the addition of (Z)-9-hexadecenal to the treatment. Addition of hexadecanal or (Z)-7-hexadecenal to the initial two components had no effect in raising the behavioral response of the males in the flight tunnel whether added singularly at both the normal gland-emission ratio or at varying ratios or in combination at the normal ratio. Live, calling females elicited levels of sexual activity from males not significantly different from that elicited by the mixture of (Z)-11- and (Z)-9-hexadecenal on cotton wicks.Lepidoptera: Noctuidae.     

Identification of unique pheromone components for soybean looper mothPseudoplusia includens

Analysis of sex pheromone glands from individual female soybean looper moths showed that in addition to the previously identified main component (Z)-7-dodecenyl acetate, the compounds dodecyl acetate, 11-dodecenyl acetate, (Z)-7-dodecenyl propionate, and (Z)-7-dodecenyl butanoate were also produced. Two of the components, 12OAc and 11–12OAc, were not detected in a single analysis of female effluvium. Flight-tunnel tests showed that the five-component and three-component blends were equal to each other and to a female extract (> 80% source contacts) and that the mixtures were superior toZ7–12OAc alone. Field tests indicated that the five-component blend was significantly more attractive thanZ7–12OAc alone at a dosage of 1 mg, but that the blend was only slightly better at 3 mg.     

Specificity of male response to multicomponent pheromones in noctuid mothsTrichoplusia ni andPseudoplusia includens

The response of male cabbage looper (CL) and soybean iooper (SBL) moths was observed in the flight tunnel and measured in field tests to the six-component CL pheromone, the five-component SBL pheromone, and toZ7–12: OAc, the major component common to each pheromone. In both the flight tunnel and the field, male CL exhibited significantly greater levels of response to their six-component blend than toZ7–12: OAc alone. A low level of cross-attraction of male CL to the SBL pheromone was observed in both the flight tunnel and the field, but it was quantitatively and qualitatively similar to their response toZ7–12: OAc alone. Thus the minor components of the SBL blend did not appear to disrupt the flight behavior of male CL. With respect to SBL, in the flight tunnel males also exhibited a greater level of response to the five-component blend compared toZ7–12: OAc, but in the field their response was not significantly different to either treatment. There was also a low level of cross-attraction of male SBL to the CL blend, but this appeared to involve a significant arrestment effect on the upwind flight of males, as well as a difference in male sensitivity to the blend of components compared withZ7–12: OAc alone. The observed arrestment effect may have been due to male perception of one or more minor components of the CL pheromone. The results show that the multicomponent pheromones of these species function effectively as specific mating signals and that discrimination of odor quality by male moths can occur as the result of minor components affecting male sensitivity or their upwind flight response to the pheromone.     

Trade-Off Between Sensitivity and Specificity in the Cabbage Looper Moth Response to Sex Pheromone

The evolution of male moth responses to pheromone blends may be constrained by a trade-off between two response traits: sensitivity and breadth of response. Population genetic simulations predict that if sensitivity and breadth of response are negatively correlated (i.e., a trade-off exists), then selection will favor males with narrow response phenotypes and high sensitivity. Although sensitivity-breadth of response trade-offs are generally assumed to exist and are implicit to the shape of male preference function, this study is the first to provide empirical support measuring behavior at the level of the individual. Previous studies with the cabbage looper, Trichoplusia ni, have documented the existence of a mutant pheromone strain. While mutant females produce a pheromone blend significantly different from wild-type females, mutant males respond equally to the wild-type and mutant pheromone blends. This study used wind tunnel bioassays to document that relative to wild-type males, mutant males had broader response profiles but lower pheromone sensitivity. While wild-type male responses were highest to the wild-type pheromone blend, mutant males did not discriminate among pheromone blends. These results are consistent with a trade-off between breadth of response and sensitivity. Pure wild-type and mutant lines were crossed and hybrid males assayed. Both hybrid types (maternal wild-type and maternal mutant hybrids) responded similarly. Hybrid males had response profiles similar to wild-type males and the reduced sensitivity observed in mutant males. These results suggest a possible hybrid disadvantage and a putative mechanism for reinforcement of male pheromone response traits.     

Compound interactions effects of plant antioxidants in combination with carbaryl on performance ofTrichoplusia ni (Cabbage Looper)

Plant chemicals naturally exist in complex mixtures, which can interact either additively, synergistically, or antagonistically. We investigated the potential interactions of three naturally occurring antioxidants— nordihydroguaiaretic acid (NDGA), safrole, and -tocopherol—with the general insecticide carbarayl to affect the performance of cabbage looper larvae (Trichoplusia ni). The cabbage looper is known to produce a mixed-function oxidase enzyme system in response to the presence of carbaryl. We proposed that plant antioxidants would interfere with enzymatic oxidation, enhancing the susceptibility of this insect to carbaryl. Insects were fed artificial diets containing each antioxidant alone or in pairwise combinations with the insecticide carbaryl to test for their effects on the insect's nutritional measurement indices. The three antioxidants tested were not equally effective individually against insect survivorship and interacted differentially in combination with the insecticide. The nutritional indices were measured on insects fed diets containing the chemicals at nonlethal doses. Insects fed 0.001 % wet wt NDGA diets grew 1.62 times less, and had gross and net conversion efficiencies reduced 3.20 and 3.63 times, respectively, compared to the control larvae. Carbaryl (0.002% wet wt) in combination with NDGA acts as an antagonist to the effects mentioned above, while safrole (1 × 10^–4 wet wt) had an additive effect when combined with the insecticide, reducing 1.76 times larval relative growth rate and efficiency of conversion of ingested food in respect to the control. The larvae fed significantly more (1.2 times) on both insecticide and safrole diets than on the controls or their combined diets. Larvae fed -tocopherol alone or in combination with carbaryl had similar growth and conversion efficiencies as controls. We conclude that the effects of different combinations of compounds cannot be predicted a priori and must be determined experimentally.Operated for the U.S. Department of Energy by the University of California under Contract No. DE-ACO3-76-SF00012. This article was supported by the Center for Intermedia Transport Research (EPA Contract CR-81172-01) and by the Ecological Research Division of the Office of Health and Environmental Research, U.S. Department of Energy.     

Insect olfactory receptor responses to components of pheromone blends

Multicomponent pheromone systems are common in many insect species. As our knowledge about the number of different chemical compounds actually involved in a particular communication system increases, so too does the need for an efficient neural mechanism for the encoding of behaviorially relevant odor compounds. Here we consider the electrical activity of olfactory receptor neurons in a subset of the individual pheromone-sensitive sensilla on the antennae of male cabbage looper moths (Trichoplupia ni). Responses to single- and multiple-component stimuli, drawn from seven behaviorally active compounds, were obtained at several different intensities. Some blends elicited electrical responses which were not readily predicted from a knowledge of the receptor neuron's response to individual components.