Intraspecific alkaloid variation in ladybird eggs and its effects on con- and hetero-specific intraguild predators.

Egg predation and cannibalism are common phenomena in predatory ladybirds despite the presence of defensive alkaloids. Consumption of heterospecific eggs negatively affects survivorship and development; however, intraspecific variation in quantities of alkaloids and post-ingestion responses to con- and hetero-specific alkaloids, are not well understood. We examined variation in the quantity of alkaloids in eggs of Harmonia axyridis (Pallas), Coccinella septempunctata L., and Hippodamia convergens (Guérin) using gas chromatography-mass spectrometry, and show a link between heterospecific alkaloids and their toxicity and/or costs by feeding high and low alkaloid eggs to first instar H. axyridis and C. septempunctata. The repeatability of alkaloid measurements in eggs in an egg cluster was high; however, the amount of alkaloids varied significantly between egg clutches within and among females. This variation affected egg consumption by C. septempunctata when fed H. axyridis eggs. Harmonia axyridis accumulated their own alkaloid by cannibalism and synthesized it de novo, but C. septempunctata lost some portion of the consumed conspecific alkaloids. Both species lost most of the consumed heterospecific alkaloids, but C. septempunctata died within 3 days. Most H. axyridis survived to the second instar, but C. septempunctata alkaloids led to a significant reduction in weight gain compared to an aphid control. In addition, ingestion of high alkaloid C. septempunctata extended development of H. axyridis compared to the aphid control or conspecific eggs. Harmonia axyridis had greater abilities to process ingested con- and hetero-specific alkaloids compared with C. septempunctata, which may, in part, explain their interspecific interactions in nature.

Quantitative genetics of signal evolution: a comparison of the pheromonal signal in two populations of the cabbage looper, Trichoplusia ni.

Pheromones are important in reproductive isolation among populations of moths, but the genetics associated with diversification of pheromonal signals is poorly understood. To gain insight into processes that may lead to diversification we examined the genetic architecture underlying the production of the sex pheromone of the cabbage looper moth, Trichoplusia ni. We compared genetic parameters of two populations; one with a wild-type pheromone phenotype (N) and one where a single-gene mutation affecting the pheromone blend produced by females had been established (M). Using a half-sib breeding design we estimated heritabilities, coefficients of additive genetic variation, and phenotypic, genetic, and environmental correlations of the pheromone components. In both populations, narrow sense heritabilities were generally moderate and genetic correlations were mostly positive. Comparisons between the two populations showed that, while the pattern of phenotypic correlations showed significant agreement between populations, the patterns of genetic (co)variation (i.e. the shapes of the within population matrix) were dissimilar between the two populations. The presence of additive genetic variation in both populations indicates that there is the potential for further evolution of individual pheromone components. However, because of the differences between the populations in the pattern of genetic variation and covariation, the populations will evolve along different evolutionary trajectories even under identical selection pressures. These results suggest that single gene mutations, once established, can be associated with further alterations in the genetic architecture and this has implications for the evolution of pheromone communication.

Does PBAN play an alternative role of controlling pheromone emission in the cabbage looper moth, Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae)?

There is an active process by which sex pheromone reserves of female cabbage looper moths, Trichoplusia ni, are transported to the gland's surface during the nocturnal period of calling. We hypothesized that this mobilization was controlled by a head factor, possibly related to the pheromone biosynthesis activating neuropeptides (PBAN) that in other species stimulate pheromone synthesis. We evaluated the impact of head extracts of T. ni on pheromone emission and glandular content of pheromone. During the photophase injected head extracts stimulated an increased pheromone emission rate in females, but glandular content of pheromone was not affected. Head extracts of H. virescens, a species with known PBAN activity, and synthetic PBAN stimulated an increased pheromone emission rate in T. ni. There was some specificity of the response of female T. ni to PBAN, in that several other unrelated polypeptides did not stimulate this type of response. Previously it had been determined that brain factors do not play a role in stimulating pheromone biosynthesis in T. ni. Our results indicate that there may be additional avenues by which PBAN or related neuropeptides control pheromone emission, including transport of pheromone reserves to the surface of the sex pheromone gland.

Identification of sex pheromone ofTetanolita mynesalis (Lepidoptera: Noctuidae), a prey species of bolas spider,Mastophora hutchinsoni.

The bolas spider,Mastophora hutchinsoni, attracts adult males of four species of nocturnally active Lepidoptera through aggressive chemical mimicry of those species' sex pheromones. Here we report the identification of the sex pheromone of one prey species, the smoky tetanolita (Tetanolita mynesalis). In sex pheromone gland extracts, only two peaks stimulated an electrophysiological response as measured by a coupled gas chromatography-electroantennographic detection analysis. These two peaks had retention times identical to (3Z,6Z,9Z)-heneicosatriene (3Z,6Z,9Z-21:H) and (3Z,9Z)-cis-6,7-epoxy-heneicosadiene (3Z,9Z-cis-6,7-epoxy-21:H), respectively, and mass spectra identical to these two compounds. It was determined that 0.23±0.16 and 0.56±0.26 ng of 3Z,6Z,9Z-21:H and 3Z,9Z-cis-6,7-epoxy-21:H, respectively, were present in pheromone gland extracts from individual females. A 1:1 blend of 3Z,6Z,9Z-21:H and 3Z,9Z-6S,7R-epoxy-21:H was an effective attractant for adult males from feral populations. Blend ratios of these two components from 2:1 to 1:2 were equally effective as attractants. Greater deviation from the optimal blends resulted in diminished trap catches. The enantiomer 3Z,9Z-6R,7S-epoxy-21:H not only was not effective in attracting males, its presence in the effective blend shut down trap catches. These results indicate that the pheromone blend consists of 3Z,6Z,9Z-21:H and 3Z,9Z-6S,7R-epoxy-21:H. This is the first report of a hydrocarbon/epoxide pheromone for a prey species of this bolas spider. Sex attractants or pheromones for the other three prey species are composed of aldehydes or acetates.

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.

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.

Attraction of male beetles to grubs: Evidence for evolution of a sex pheromone from larval odor.

Females of the scarabaeid beetleCyclocephala lurida produce a volatile sex pheromone which attracts conspecific males. Field experiments demonstrated that larvae of both sexes also emit volatile chemicals that stimulate similar responses in adult males, including attempts by the attracted males to mate with the nonreproductive immature stage. Significantly more adult males were caught in traps baited with conspecific male or female larvae or adult females than in blank control traps. Hexane extracts of both male and female grubs were at least as effective as live larvae in trapping male adults, demonstrating that the behavioral responses are mediated by volatile chemicals. Sensory and behavioral responses of males to sex pheromones emitted by adult females are part of the functional communication system. However, their response to grubs is not functional, because grubs are normally temporally and spatially inaccessible to mate-seeking males. In theory, the evolution of a communication system is problematic because it requires the development of a signal in one sex and the sensory and behavioral attributes to respond to that signal in the other sex. The ontogeny of sex pheromone communication inC. lurida suggests a partial solution to this evolutionary problem. We propose that this sex pheromone communication system is probably derived from noncommunicative volatile chemicals that are lost in adult males and retained by adult females.

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 floral compounds fromAbelia grandiflora that stimulate upwind flight in cabbage looper moths.

Four major volatile components emitted from flowers ofAbelia grandiflora were identified based on retention time using two capillary columns of different polarities and electron impact mass spectrometry. These are phenylacetaldehyde, benzaldehyde, 2-phenylethanol, and benzyl alcohol. A blend of these compounds was as effective as a cluster of flowers in stimulating upwind flight by maleTrichoplusia ni to the source in a wind-tunnel test. Phenylacetaldehyde or 2-phenylethanol were each as effective as the complete blend in stimulating source location by male moths. Attraction to a source of the synthetic blend was demonstrated in virgin males and females and mated males and females, but virgin moths of both sexes were more likely than mated moths to complete the sequence of behavioral responses necessary to locate the odor source.

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 (Z7-12∶Ac). 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 (Z5-12∶Ac) and (Z)-7-tetradecenyl acetate (Z7-14∶Ac) 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 Z5-12∶Ac, Z7-14∶Ac, and Z9-14∶Ac 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.

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.

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.

Identification of sex pheromone of bristly cutworm,Lacinipolia renigera (Stephens).

The sex pheromone of the bristly cutworm moth,Lacinipolia renigera was identified as a blend of (Z)-9-tetradecenyl acetate (itZ9-14): Ac and (Z, E)-9,12-tetradecadienyl acetate (ZE-9,12-14: Ac). Extracts of female glands were analyzed by capillary gas chromatography on three columns of different polarities. In each analysis, peaks with retention times identical to Z9-14:Ac andZE-9, 12-14: Ac were observed. GC-MS analysis of gland extracts supported the identification of these two compounds. Volatiles emitted from female sex pheromone glands during 10-min collection periods contained 7.8 ±2.01 ng ofZ9- 14: Ac. On average the blend contained 3.8 ± 1.43%ZE-9,12-14: Ac. Blends ranging from 1% to 10%ZE- 9,12-14: Ac in Z9-14: Ac (1 mg) were effective in capturing males in the field. The number of males captured in traps baited with a 3 % blend ofZE- 9,12-14: Ac in Z9-14: Ac was not significantly different than the number caught in traps containing two virgin females.

Potential for evolution of resistance to pheromones : Worldwide and local variation in chemical communication system of pink bollworm moth,Pectinophora gossypiella.

FemalePectinophora gossypiella (Saunders) from most of the desert cotton-growing areas of southern California emitted significantly more pheromone in 1984 and 1985 than in preceding years (1982 and 1983). This increase amounted to almost 20% by 1985. It is unlikely that this small change would represent effective resistance to disruptant pheromones, but this increase could reflect the result of selection pressure imposed by the use of mating disruption for population control. A worldwide survey of emitted pheromone from this species found that there was much more variation in the emission rate than the blend ratio of the two pheromone components. The emitted blend ratio was remarkably consistent over time (in southern California) and throughout the worldwide range of the insect. Small differences in the blend ratio that were detected probably have no major biological significance because of the relatively broad response spectrum of males to changes in the blend of pheromonal components. Populations of males did not consist of several phenotypes, each with a different preference for specific blend ratios. Rather, the broad response spectrum to blend ratios in a population can be attributed to variation in the response of any individual. Therefore, selection for a response phenotype that is narrowly tuned to the blend emitted by females may be difficult.

Identification of sex pheromone of calendula plume mothPlatyptilia williamsii.

The sex pheromone of the calendula plume moth,Platyptilia williamsii was identified as (Z)-11-hexadecenal (Z11-16∶Aid). Extracts of female sex pheromone glands contained several compounds when analyzed by capillary and packed-column GLC. However, airborne collections of volatiles from glands contained only one of these compounds, having the same retention time asZ11-16∶Ald. GC-MS and microozonolysis analyses of the natural product were consistent with those of syntheticZ11-16∶Ald. In a flight tunnel, males oriented upwind and touched sources ofZ11-16∶Ald and gland extract with equal frequency. Field tests of syntheticZ11-16∶Ald already have shown it to be a potent sex attractant for males of this species. This study further supports the hypothesis thatP. williamsii and a sympatric species,Platyptilia carduidactyla, are not reproductively isolated by chemical differences in the composition of the sex pheromone, but rather by temporal differences in sexual activities.

Sensory and behavioral effects of gossyplure alcohol on sex pheromone response of male pink bollworm moths,Pectinophora gossypiella.

(Z,Z)- and (Z,E)-7,11-hexadecadienol, reported to be pheromone precursors, interfere with the normal sequence of behavioral response of malePectinophora gossypiella to sex pheromone. The magnitude of the interference can be diminished with higher release rates of the sex pheromone. (Z,Z)-7,11-Hexadecadienol is more effective than itsZ,E isomer in eliciting the reduction in the behavioral response. Electroantennographic evidence suggests that each alcohol may be interfering more with receptor sites for the conformationally similar pheromone acetate than with receptor sites for the other pheromone isomer. Defining behavioral and physiological effects of pheromone analogs such as the alcohols of gossyplure may help to determine their potential for behavioral manipulations.

Potential for evolution of resistance to pheromones: Interindividual and interpopulational variation in chemical communication system of pink bollworm moth.

After an extensive examination of the release rates and blend ratios of pheromonal components emitted by field-collected femalePectinophora gossypiella (Saunders), we find no evidence of resistance to pheromones applied to cotton fields to disrupt mating. Females from fields with 3-5 years of exposure to disruptant pheromones as well as those from fields with only minimal exposure to disruptant pheromones emitted (Z,Z)-7,11-hexadecadienyl acetate at a rate of ca. 0.1 ng/min and (Z,E)7,11-hexadecadienyl acetate at ca. 0.06 ng/min. The ratio of pheromonal components was much less variable than the measured emission rate and was centered about a 61:39Z, Z to Z,E ratio. In contrast to the blend ratio emitted by females, the composition of the pheromonal blend used in monitoring populations and disrupting mating is centered about 50:50 Z,Z to Z.E. In general there was a remarkable consistency in the release rate and blend ratio among populations of females throughout southern California and those from a laboratory colony. It would appear that, although resistance to theP. gossypiella pheromone is still a very real possibility when it is used heavily in pest management as a mating disruptant, there are current agricultural practices and conditions which would hinder its development.

Ultraviolet enhanced reactivation of a human virus: effect of delayed infection.

The ability of UV-irradiated herpes simplex virus to form plaques was examined in monolayers of CV-1 monkey kidney cells preexposed to UV radiation at different intervals before virus assay. From analysis of UV reactivation (Weigle reactivation) curves it was found that as the interval between cell UV irradiation (0-20 J/m2) and initiation of the virus assay was increased over a period of five days, (1) the capacity of the cells to support unirradiated virus plaque formation, which was decreased immediately following UV exposure to the monolayers, increased and returned to approximately normal levels within five days, and (2) at five days an exponential increase was observed in the relative plaque formation of irradiated virus as a function of UV fluence to the monolayers. For high UV fluence (20 J/m2) to the cells, the relative plaque formation by the UV-irradiated virus at five days was about 10-fold higher than that obtained from assay on unirradiated cells. This enhancement in plaque formation is interpreted as a delayed expression of Weigle reactivation. The amount of enhancement resulting from this delayed reactivation was several fold greater than that produced by the Weigle reactivation which occurred when irradiated herpes virus was assayed immediately following cell irradiation.