An analytical model for genetic control of Heliothis virescens incorporating the effects of sterile males

Summary A recent computer simulation model by Levins and Parker (1983) indicated that mass releases of male-sterile Heliothis hybrid moths could cause genetic suppression of the tobacco budworm, Heliothis virescens, without the risk of significant crop damage. We present an analytical model to explore the behavior of the Levins-Parker model. Our model shows that the length of time between matings for females when they mate with wild type fertile males to that when they mate with hybrid sterile males is extremely important to the efficacy of a suppression program. Release ratios needed to suppress a natural pest population were examined across a range of biological parameters.     

Association of a sperm-specific protein with the mitochondrial F1F0-ATPase in Heliothis: Implications for sterility of H. virescens × H. subflexa backcross hybrids

Evidence is presented that a mitochondrial protein that displays a species-specific net charge in the Heliothis spp complex is associated with subunits of the F₁-ATPase. The expression of this 63 kd polypeptide, p63, was restricted to sperm and its developmental pattern of synthesis and accumulation paralleled that of the putative β-subunit of the F₁-ATPase complex. Comparisons of the enzyme from fertile Heliothis virescens and sterile (H. virescens × H. subflexa) backcross hybrid males revealed two differences. First, the specific activity of the F₁-ATPase isolated from sterile males was half that of preparations from fertile males; and second, the p63 protein was bound less tightly to the complex in backcross sperm. The implications of these findings in relation to both the identification of the cause of backcross male sterility and prospects for future research are discussed.     

A three-locus system of interspecific incompatibility underlies male inviability in hybrids between Drosophila buzzatii and D. koepferae

In hybrids between the sibling species D. buzzatii and D. koepferae, both sexes are more or less equally viable in the F₁: However, backcross males to D. buzzatii are frequently inviable, apparently because of interspecific genetic incompatibilities that are cryptic in the F₁. We have performed a genetic dissection of the effects of the X chromosome from D. koepferae. We found only two cytological regions, termed hmi-1 and hmi-2, altogether representing 9% of the whole chromosome, which when introgressed into D. buzzatii cause inviability of hybrid males. Observation of the pattern of asynapsis of polytene chromosomes (incomplete pairing, marking introgressed material) in females and segregation analyses were the technique used to infer the X chromosome regions responsible for this hybrid male inviability. The comparison of these results with those previously obtained with the same technique for hybrid male sterility in this same species pair indicate that in the X chromosome of D. koepferae there are at least seven times more regions that produce hybrid male sterility than hybrid male inviability. We have also found that the inviability brought about by the introgression of hmi-1 is suppressed by the cointrogression of two autosomal sections from D. koepferae. Apparently, these three regions conform to a system of species-specific complementary factors involved in an X-autosome interaction that, when disrupted in backcross hybrids by recombination with the genome of its sibling D. buzzatii, brings about hybrid male inviability.     

Beyond magic traits: Multimodal mating cues in Heliconius butterflies

Species coexistence involves the evolution of reproductive barriers opposing gene flow. Heliconius butterflies display colorful patterns affecting mate choice and survival through warning signaling and mimicry. These patterns are called “magic traits” for speciation because divergent natural selection may promote mimicry shifts in pattern whose role as mating cue facilitates reproductive isolation. By contrast, between comimetic species, natural selection promotes pattern convergence. We addressed whether visual convergence interferes with reproductive isolation by testing for sexual isolation between two closely related species with similar patterns, H. timareta thelxinoe and H. melpomene amaryllis. Experiments with models confirmed visual attraction based on wing phenotype, leading to indiscriminate approach. Nevertheless, mate choice experiments showed assortative mating. Monitoring male behavior toward live females revealed asymmetry in male preference, H. melpomene males courting both species equally while H. timareta males strongly preferred conspecifics. Experiments with hybrid males suggested an important genetic component for such asymmetry. Behavioral observations support a key role for short‐distance cues in determining male choice in H. timareta. Scents extracts from wings and genitalia revealed interspecific divergence in chemical signatures, and hybrid female scent composition was significantly associated with courtship intensity by H. timareta males, providing candidate chemical mating cues involved in sexual isolation.     

Contest versus scramble competition for mates: The composition and spatial structure of a population of gray mouse lemurs (Microcebus murinus) in North-west Madagascar

The modes of intrasexual competition interacting in many dispersed societies of nocturnal solitary foragers are still poorly understood. In this study we investigate the spatial structure within a free-living population of gray mouse lemurs (Microcebus murinus) in order to test for the first time the predictions from two contrasting models of male intrasexual competition on the population level. The contest competition model predicts an uneven distribution of the sexes in a population nucleus with a female biased sex ratio in the center and a male biased sex ratio in the periphery. In contrast the scramble competition model predicts males and females being distributed evenly throughout their habitat with a constant sex ratio. Nine capture/recapture periods within three consecutive mating seasons revealed a continuous male biased sex ratio in the adult population with even trapping rates for the sexes. The male biased sex ratio could either be explained with postnatal female biased mortality or with a male biased natal sex ratio. This male biased sex ratio was apparent in all parts of the study site, indicating that the population was not subdivided into a female biased core and a male biased periphery. Furthermore, the majority of adult males have been captured at the same site as or in vicinity to females. Consequently, a large proportion of males had spatial access to females during the mating season. No signs of monopolization of females by certain dominant males could be detected. These data support the predictions from the scramble competition model and the concept of a promiscuous mating system for this species.     

Identification of hemiclonal reproduction in three species of Hexagrammos marine reef fishes

Natural hybrids between the boreal species Hexagrammos octogrammus and two temperate species Hexagrammos agrammus and Hexagrammos otakii were observed frequently in southern Hokkaido, Japan. Previous studies revealed that H. octogrammus is a maternal ancestor of both hybrids; the hybrids are all fertile females and they frequently breed with paternal species. Although such rampant hybridization occurs, species boundaries have been maintained in the hybrid zone. Possible explanations for the absence of introgressions, despite the frequent backcrossing, might include clonal reproduction: parthenogenesis, gynogenesis and hybridogenesis. The natural hybrids produced haploid eggs that contained only the H. octogrammus genome (maternal ancestor) with discarded paternal genome and generated F₁‐hybrid type offspring by fertilization with the haploid sperm of H. agrammus or H. otakii (paternal ancestor). This reproductive mode was found in an artificial backcross hybrid between the natural hybrid and a male of the paternal ancestor. These findings indicate that the natural hybrids adopt hybridogenesis with high possibility and produce successive generations through hybridogenesis by backcrossing with the paternal ancestor. These hybrids of Hexagrammos represent the first hybridogenetic system found from marine fishes that widely inhabit the North Pacific Ocean. In contrast with other hybridogenetic systems, these Hexagrammos hybrids coexist with all three ancestral species in the hybrid zone. The coexistence mechanism is also discussed.     

Modeling and dynamics of Wolbachia-infected male releases and mating competition on mosquito control

Despite centuries of continuous efforts, mosquito-borne diseases (MBDs) remain enormous health threat of human life worldwide. Lately, the USA government has approved an innovative technology of releasing Wolbachia-infected male mosquitoes to suppress the wild mosquito population. In this paper we first introduce a stage-structured model for natural mosquitos, then we establish a new model considering the releasing of Wolbachia-infected male mosquitoes and the mating competition between the natural male mosquitoes and infected males on the suppression of natural mosquitoes. Dynamical analysis of the two models, including the existence and local stability of the equilibria and bifurcation analysis, reveals the existence of a forward bifurcation or a backward bifurcation with multiple attractors. Moreover, globally dynamical properties are further explored by using Lyapunov function and theory of monotone operators, respectively. Our findings suggest that infected male augmentation itself cannot always guarantee the success of population eradication, but leads to three possible levels of population suppression, so we define the corresponding suppression rate and estimate the minimum release ratio for population eradication. Furthermore, we study how the release ratio of infected males and natural ones, mating competition, the rate of cytoplasmic incompatibility and the basic offspring number affect the suppression rate of natural mosquitoes. Our results show that the successful eradication relies on assessing the reproductive capacity of natural mosquitoes, a selection of suitable Wolbachia strains and an appropriate release amount of infected males. This study will be helpful for public health authorities in designing proper strategies to control vector mosquitoes and prevent the epidemics of MBDs.

     

A comparison of responses from olfactory receptor neurons of<Emphasis Type="Italic"> Heliothis subflexa</Emphasis> and<Emphasis Type="Italic"> Heliothis virescens</Emphasis> to components of their sex pheromone

Single-cell electrophysiological recordings were obtained from olfactory receptor neurons in sensilla trichodea on male antennae of the heliothine species Heliothis subflexa and the closely related congener H. virescens. A large percentage of sensilla (72% and 81%, respectively, of all sensilla sampled) contained a single odor-responsive receptor neuron tuned to the major pheromone component of both species, Z-11-hexadecenal. A second population of sensilla on H. subflexa antennae (18%) housed receptor neurons that were tuned to Z-9-hexadecenal but also responded with less sensitivity to Z-9-tetradecenal. A similar population of sensilla (4%) on H. virescens male antennae housed receptor neurons that were shown to be tuned specifically only to Z-9-tetradecenal, with no response to even high dosages of Z-9-hexadecenal. A third population of sensilla (comprising 8% and 16% of the sensilla sampled in H. subflexa and H. virescens, respectively) housed two olfactory receptor neurons, one of which was tuned to Z-11-hexadecenyl acetate and the other tuned to Z-11-hexadecenol. In H. subflexa the Z-11-hexadecenyl acetate-tuned neuron also responded to Z-9-tetradecenal with nearly equivalent sensitivity. The behavioral requirements of males of these two species for distinct pheromonal blends was, therefore, reflected by the subtle differences in the tuning properties of antennal olfactory receptor neurons.Abbreviations MGC macroglomerular complex - ORN olfactory receptor neuron - Z9–14:Ald (Z)-9-tetradecenal - Z9–16:Ald (Z)-9-hexadecenal - Z11–16:Ac (Z)-11-hexadecenyl acetate - Z11–16:Ald (Z)-11-hexadecenal - Z11–16:OH (Z)-11-hexadecenol     

The genetic basis of host range inHeliothis virescens: larval survival and growth

Larval feeding was assayed in a generalist caterpillar (Heliothis virescens (F.)), a specialist caterpillar (Heliothis subflexa (Gn.)), their F₁ hybrids and a backcross withH. s. to gain a preliminary understanding of the genetic basis of host use inH. v. Plants used in these experiments were tobacco (Nicotiana tabaccum), cotton (Gossypium hirsutum), soybean (Glycine max) (hosts ofH. v.) and ground cherry (Physalis pubescens) (host ofH.s.). A feeding study ofH.v., H.s. and their reciprocal hybrids showed that, after the first eight days of feeding,H.v. had its highest survival and weight gain on soybean and had lowest survival and weight gain on its non-host,Physalis. H.s. had its highest survival and weight gain on its host plant,Physalis, and performed very poorly on the three non-host plants. The two F₁ hybrids were SV₀ (offspring ofH.s. female andH.v. male) and VS₀ (offspring ofH.v. female andH.s. male). The hybrids did not differ from each other, indicating no sex linkage or maternal effects, except that VS₀ had greater weight gain on tobacco than did SV₀. The hybrids, unlike their parents, survived well on all four host plants and their weight gain was intermediate on all four host plants. In a separate experiment the VS₀ hybrid was mated to the specialist to produce the VS₁ backcross. In contrast to the F₁, the backcross had significantly lower survival than the generalist on soybean, cotton, tobacco and weight gain was lower on soybean, cotton and tobacco but higher onPhysalis. Survival and weight gain on cotton and tobacco were inherited as partially dominant traits; onPhysalis there was overdominance for survival and complete dominance for weight gain; on soybean both survival and weight gain were additive. Survival on cotton,Physalis, soybean and tobacco and weight gain onPhysalis could not be completely explained by a model that included only dominance and additive effects. These traits may be influenced by epistatic and/or environmental effects.     

THE GENETIC ARCHITECTURE OF A COMPLEX ECOLOGICAL TRAIT: HOST PLANT USE IN THE SPECIALIST MOTH,HELIOTHIS SUBFLEXA

We used genetic mapping to examine the genetic architecture of differences in host plant use between two species of noctuid moths, Heliothis subflexa, a specialist on Physalis spp., and its close relative, the broad generalist H. virescens. We introgressed H. subflexa chromosomes into the H. virescens background and analyzed 1462 backcross insects. The effects of H. subflexa‐origin chromosomes were small when measured as the percent variation explained in backcross populations (0.2–5%), but were larger when considered in relation to the interspecific difference explained (1.5–165%). Most significant chromosomes had effects on more than one trait, and their effects varied between years, sexes, and genetic backgrounds. Different chromosomes could produce similar phenotypes, suggesting that the same trait might be controlled by different chromosomes in different backcross populations. It appears that many loci of small effect contribute to the use of Physalis by H. subflexa. We hypothesize that behavioral changes may have paved the way for physiological adaptation to Physalis by the generalist ancestor of H. subflexa and H. virescens.     

Differential response of Trichogramma wasps to extreme sex pheromone types of the noctuid moth Heliothis virescens

1. Chemical espionage in nature may occur when predators or parasitoids home in on animal or plant communication signals. Parasitoid wasps are known to use pheromones emitted by adults hosts to locate host eggs, larvae or pupae. The response of Trichogramma egg parasitoids to a synthetic sex pheromone blend of moths has been shown in a number of studies over the past 40 years. 2. Trichogramma pretiosum (Hymenoptera, Trichogrammatidae) is a tiny parasitic wasp, attacking the eggs of the noctuid moth Heliothis virescens (Lepidoptera, Noctuidae). This study investigated whether T. pretiosum homes in on the sex pheromone of H. virescens at close range. The arrestment response of the wasps to sex pheromone gland extracts of two types of female moths, so‐called high and low females, was also tested, referring to two selected extreme pheromone types of H. virescens. The study also investigated whether the wasps would mount females, possibly to hitchhike with them. 3. The wasps were arrested by the common, ‘low’ pheromone, but not by the rare, ‘high’ pheromone or by extracts from male hairpencils. The wasps did not show a preference for separate sex pheromone compounds, but when pre‐exposed to the major sex pheromone component of H. virescens before the tests together with H. virescens eggs, they did show a preference, indicating learning behaviour. In the mounting experiments, mated females were mounted significantly more than virgin females or males, suggesting that hitchhiking is a strategy used by these wasps to locate moth eggs. 4. This represents the first study to show a differential response of parasitoid wasps to two different sex pheromone types in a single host species. The results warrant further investigations into the potential role of parasitic wasps in the evolution of sexual communication in moths.     

Comparative reproduction and nonparasitic development of Boophilus microplus and hybridized Boophilus ticks (Acari: Ixodidae) under natural field conditions in subtropical South Texas

The reproductive biology and nonparasitic development of Boophilus microplus (Canestrini) and hybridized Boophilus ticks (B. annulatus (Say) male x B. microplus female) held under natural field conditions in south Texas throughout the year were compared. Comparisons between the two types of ticks indicated that the ovipositional biology (percentage of ovipositing females and number of eggs laid) of the females favored hybrid ticks during some months and B. microplus ticks during other months. However, on a yearlong basis, there was virtually no difference in the percentage of ovipositing females or in the number of eggs deposited by hybrid females as compared to B. microplus. The duration of each nonparasitic development period (preoviposition period, incubation period of eggs, and larval longevity) showed that both types of ticks had very similar developmental and survival rates during the year. Generally the difference in duration of each of the nonparasitic parameters was <8 days, leading to a high degree of synchrony of the nonparasitic developmental rates between the two types of ticks. On the other hand, egg hatchability of hybrid ticks was consistently lower than pure-strain B. microplus throughout the year with significantly lower hatch rates occuring in April, July, August, October, and November. Thus, results obtained on percentage of ovipositing females, number of eggs laid, preoviposition period, incubation period of eggs, and larval longevity provide positive encouragement for the possible use of sterile hybrid males as a means of eliminating a native B. microplus population. In contrast, results of the egg hatchability of the two types of ticks indicate that the selective advantage afforded toB. microplus could have an adverse affect on the success of a sterile hybrid male program by making the number of hybrid ticks necessary to eliminate a native population prohibitively high.This paper reports the results of research only. Mention of a commercial or a proprietary product in this paper does not constitute an endorsement by the US Department of Agriculture.     

Sex ratio,survival, and recapture rate in a Cuban population of the damselfly <Emphasis Type="BoldItalic">Hypolestes trinitatis</Emphasis> (Odonata: Megapodagrionidae)

Male-biased sex ratios in adult odonate populations have been the subject of vigorous discussion between the students of this order of insects. The debate has centered on whether the observed male bias in many populations is real, perhaps due to unequal survival rates, or whether it is an artifact caused by differences in recapture probabilities. A mark–recapture study to assess the relative contribution of survivorship and recapture rates on male-biased sex ratio was performed in a Cuban population of the damselfly Hypolestes trinitatis. Maximum likelihood theory and Akaike information criterion were used for parameter estimation and model selection, respectively. Females in the sample were outnumbered two to one by males. Estimated recapture and survival rates were 0.188 (females) and 0.638 (males), and 0.933 (females) and 0.944 (males), respectively. Recapture rates only partially explained the bias since the population sex ratio estimated after correcting for differences in this parameter was male biased (1.5). The observed higher survival probabilities in males could have generated the male-biased population sex ratio. Therefore, we concluded that the observed male-biased population sex ratio in H. trinitatis is real.     

Sex ratio from germination through maturity and its reproductive consequences in the liverwort Sphaerocarpos texanus

Summary The dioecious winter ephemeral liverwort, Sphaerocarpos texanus disperses spore tetrads consisting of two males and two females. I examined the subsequent sex ratio of S. texanus at different stages in its life cycle to detect possible mechanisms affecting deviations from a 1:1 sex ratio and the effect of sex ratio on reproductive success. As S. texanus occurs in pure male, pure female and mixed sex clumps, I examined the proportions and sizes of these, the reproductive success of pure female and mixed sex clumps in the field and the sex ratio of germinating plants in a growth chamber. In both the field and the growth chamber the most abundant clump type was pure female followed by mixed sex and pure male clumps. These abundance patterns suggest that males have a lower survival rate than females before emergence and this lower survival rate continues through the gametophytic stage. This disadvantage may be due to the higher susceptibility of males to environmental conditions, to their competitive inferiority to females, and/or to differential resource allocation to the sexes within the spore tetrad. The female biased sex ratio at germination is consistent with predictions from sex ratio theory. Further my field data indicate that males may gain a survival benefit from growing in a mixed sex clump and both males and females benefit reproductively when they occur in mixed sex clumps.     

民勤绿洲荒漠过渡带人工梭梭种群年龄结构及动态

基于野外样地调查数据,通过分析静态生命表、存活曲线、动态指数等参数,结合时间序列模型,研究了人工梭梭种群年龄结构动态,旨在预测人工梭梭种群演替趋势,为退化人工梭梭种群恢复与重建提供理论依据。结果表明：(1)民勤绿洲荒漠过渡带人工梭梭种群的年龄结构近似于“金字塔”型,幼龄林个体占总物种数的90.1%;(2)人工梭梭种群存活曲线趋近于Deevey-Ⅱ型,为稳定型种群。不同区域人工梭梭种群的第Ⅰ、Ⅱ、Ⅲ龄级个体死亡率和消失率最高;(3)动态量化结果显示人工梭梭种群总体均表现为增长型,对外界干扰敏感性较强;(4)时间序列预测分析表明,在未来2、4个龄级时间后,种群Ⅱ、Ⅳ龄级个体数量大幅度增加,人工梭梭种群发展趋势较好。民勤绿洲荒漠过渡带人工梭梭种群为稳定增长型种群,种群具有一定的自然更新能力。针对该种群幼龄个体死亡率较高的问题,未来建议加强对第Ⅰ、Ⅱ、Ⅲ龄级幼株的精准抚育管理,通过人为辅助措施提高幼苗的保存率,促进人工梭梭林的可持续发展。     

Proximate causes of sexual size dimorphism in Colorado pikeminnow, a long‐lived cyprinid

Evidence for sexual size dimorphism (SSD) and its possible causes were examined in the endangered Colorado pikeminnow Ptychocheilus lucius, a large, piscivorous, cyprinid endemic to the Colorado River system of North America. Individuals representing 18–24% of the upper Colorado River population were captured, measured, sexed and released in 1999 and 2000. Differing male and female total length‐(L_T) frequency distributions revealed SSD with females having greater mean and maximum sizes than males. Although both sexes exhibit indeterminate post‐maturity growth, growth trajectories differed. The point of trajectory divergence was not established, but slowed male growth might coincide with the onset of maturation. Differing growth rate was the dominant proximate cause of SSD, accounting for an estimated 61% of the observed difference in mean adult L_T. The degree of SSD in adults, however, was also related to two other factors. Evidence suggests males become sexually active at a smaller size and earlier age than females; a 2 year difference, suggested here, accounted for an estimated 12% of the between‐sex difference in mean adult L_T. Temporal shifts in gender‐specific survival accounted for an additional 27% of the observed between‐sex difference in mean adult L_T. Estimated age distributions indicated a higher number of older females than older males and more younger males than younger females in the population during the period of sampling. Dissimilarity of age distributions was an unexpected result because the male : female population sex ratio was 1 : 1 and estimates of long‐term annual survival for adult males and females were equal (88%). Future assessments of SSD in this population are apt to vary depending on the prior history of short‐term gender‐specific survival. Without recognizing SSD, non‐gender‐specific growth curves overestimate mean age of adult females and underestimate mean age of adult males of given L_T. Assuming age 8 years for first reproduction in males and age 10 years for females, the adult male : female ratio was estimated as 1·1 : 1 and mean adult age, or generation time, was estimated as 16·4 years for males and 18·4 years for females.     

Genetics of sexual isolation based on courtship song between two sympatric species: Drosophila ananassae and D. pallidosa

Sexual isolation has been considered one of the primary causes of speciation and its genetic study has the potential to reveal the genetics of speciation. In Drosophila, the importance of courtship songs in sexual isolation between closely related species has been well investigated, but studies analysing the genetic basis of the difference in the courtship songs associated with sexual isolation are less well documented. Drosophila ananassae and Drosophila pallidosa are useful for studies of sexual isolation, because of their sympatric distribution and absence of postmating isolation. Courtship songs are known to play a crucial role in sexual isolation between these two species, and the female discrimination behaviour against the courting male has been revealed to be controlled by a very narrow region on the second chromosome. In this study we investigated the genetic basis controlling the song differences associated with their sexual isolation, using intact and wingless males with chromosomes substituted between species. The results obtained from F₁ hybrid males between these species indicate the dominance of the song characters favoured by D. pallidosa females. In addition, the results obtained from backcross F₂ males indicate that chromosome 2 had a major effect on the control of the song characters associated with sexual isolation.     

Fertility in first-generation hybrids of roach, Rutilus rutilus (L.), and silver bream, Blicca bjoerkna (L.)

Fertility in first‐generation hybrids of roach, Rutilus rutilus, and silver bream, Blicca bjoerkna, was investigated. Sperm and egg production of hybrids at first sexual maturity were examined. Eggs from female hybrids were artificially fertilized with the sperm of a corresponding hybrid male; a hybrid male from the reciprocal crossbreeding; a parental species male R. rutilus; and a parental species male B. bjoerkna. The results revealed that gametogenesis was normal in female hybrids. However, in male hybrids, a low efficiency of gametogenesis was observed. The semen of male hybrids was extremely dilute, with spermatozoa concentration lower than that in parental species. Nevertheless, these F1 hybrids (males and females) from reciprocal crossbreeding were fertile. F2 and backcross generations were produced, but F2 crosses from the female hybrid and corresponding hybrid male displayed a drastically slower hatching rate. Also higher proportions of deformed embryos were hatched than in other post‐F1‐generation crosses.     

Investigations into the natural infection rate of <Emphasis Type="Italic">Haemaphysalis qinghaiensis</Emphasis> with Piroplasma using a nested PCR

Here we describe the natural infection rate in China of Haemaphysalis qinghaiensis with four Piroplasma species, namely Theileria uilenbergi, T. luwenshuni, T. sinensis and Babesia motasi. Specifically, a nested PCR was designed based on 18S ribosomal RNA genes and its specificity and sensitivity were established. The result showed that 62 flat adult field H. qinghaiensis ticks (27 females and 35 males) out of 136 (55 females and 81 males) were infected by one or more parasites. All 62 (45.6%) were infected with T. uilenbergi; nine (five males and four females; 6.6%) were infected with T. luwenshuni; two (1.5%) females were infected with T. sinensis; and one (0.7%) male was infected with B. motasi. Twelve (19.4%) were infected with more than one pathogen. There was no significant difference in infection rate between males and females. The high figure 45.6% Theileria infection rate indicates the serious prevalence of theileriosis; while the presence of T. sinensis and B. motasi implies the potential existence of the corresponding diseases in the area studied.     

Responses of male Helicoverpa zea to single pulses of sex pheromone and behavioural antagonist

Male Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) flying in a pheromone plume respond to the loss of pheromone when they fly into a large pocket of clean air by going into crosswind casting flight in a mean of 0.48 s; 0.62 s after re‐contacting pheromone presented as a single pulse, they surge upwind in a kind of narrow zigzagging flight. After 0.36 s of surging, they lapse into casting flight once again in the clean air following the pulse. The addition of a known behavioural antagonist (Z)‐11‐hexadecenyl acetate (Z11–16:Ac), to the pheromone significantly increases the mean latency of the response to a single pulse to 0.85 s. No other aspects of the surge were significantly changed by the presence of antagonist in the single pulse of pheromone. Thus, unlike males of the related species, Heliothis virescens, which show significant changes in track and course angles when antagonist is present in single pulses, only an increased latency of response to a filament containing antagonist occurred in H. zea males. The increased latency could act cumulatively when the male is exposed rapidly and repeatedly to filaments in a natural plume and explain the profound arrestment effect of the antagonist in such plumes. The latencies to casting and surging in response to a pulse of pheromone blend are longer than those of the smaller species, H. virescens, and may be due to size‐related differences in manoeuverability of H. zea vs. H. virescens.