César Gemeno

Role of bacteria in mediating the oviposition responses of Aedes albopictus (Diptera: Culicidae).

Abstract The responses of Aedes albopictus to sources of oviposition attractants and stimulants were evaluated with a behavioral bioassay in which females attracted to odorants emanating from water were trapped on screens coated with an adhesive. Gravid mosquitoes were attracted to volatiles from larval-rearing water and soil-contaminated cotton towels. Bacteria were isolated from these substrates and from an organic infusion made with oak leaves. Through fatty acid-methyl ester analyses, six bacterial isolates from larval-rearing water, two isolates from soil-contaminated cotton towels, and three isolates from oak leaf infusion were identified to species. The response of gravid mosquitoes to these isolates was also evaluated in behavioral bioassays. Water containing Psychrobacter immobilis (from larval-rearing water), Sphingobacterium multivorum (from soil-contaminated cotton towels), and an undetermined Bacillus species (from oak leaf infusion) elicited significantly higher oviposition than control water without bacteria. Only volatiles collected from larval rearing water elicited significant electroantennogram responses in females.

Aggressive chemical mimicry of moth pheromones by a bolas spider: how does this specialist predator attract more than one species of prey?

SummaryThe bolas spider, Mastophora hutchinsoni, attracts Lacinipolia renigera and Tetanolita mynesalis males by mimicking the female moth sex pheromones. However, as the prey species use completely different pheromone blends we conducted experiments to determine how this is accomplished by the predator. The periodicity of L. renigera mate-seeking activities occurs early in the scotophase, whereas male T. mynesalis are active late at night, corresponding with periods when these moths are captured by the spider. The pheromone blend of early-flying L. renigera interferes with attraction of late-flying T. mynesalis to its pheromone in a dose-dependent manner, suggesting the spider must always produce a single sub-optimal “compromise” blend for both species or that it adjusts its allomonal blend to optimize capture of the respective prey species at different times during the night. We delayed (L. renigera) or advanced (T. mynesalis) the periodicity of male activity through photoperiodic manipulation and found that the bolas spider attracted both prey species outside their normal activity windows. These results support the idea that bolas spiders produce components of both species at all times rather than producing the pheromone of each prey species at different times of the night. However, using coupled gas chromatography-electroantennography, we also demonstrated that the spider decreases its emission of the L. renigera pheromone over the course of the night. This modification should reduce the behavioral antagonism of the L. renigera pheromone on T. mynesalis males and increase the predators success of attracting T. mynesalis during this preys normal activity window late at night.

Synergism of pheromone and host-plant volatile blends in the attraction of Grapholita molesta males

Control of Grapholita molesta (Busck) (Lepidoptera: Tortricidae), a major pest of stone and pome fruits, is successfully achieved by mating disruption. Under these conditions, tools other than conventional pheromone dispensers are needed for flight monitoring. The objective of the present work was to determine whether plant volatiles synergize male G. molesta attraction to a suboptimal dose of synthetic sex pheromone. The plant blend (referred to as 5VB), a mixture of three green leaf volatiles [(Z)‐3‐hexenyl acetate, (Z)‐3‐hexenol, and (E)‐2‐hexenal] and two aromatics [benzaldehyde (BZA) and benzonitrile (BZN)], was added to the suboptimal pheromone dose (2 ng on filter paper) in log steps (up to 10 000× the pheromone dose) to test synergism of pheromone and plant blends. In addition, the effect of individual plant volatiles on male responses was investigated by adding to the suboptimal pheromone dose each of the four‐compound plant‐volatile blends, resulting from eliminating one volatile from the 5VB at a time, or each plant volatile alone. Flight behaviour and the time to reach the source were recorded. The 5VB alone was not attractive to G. molesta males, but at a ratio of 1:1 000 (Ph:5VB) or higher, the attractiveness of the suboptimal pheromone dose increased, to a level similar to that of the optimal pheromone dose (10 ng). All tested plant volatiles, except BZA, synergized the response to the pheromone when added individually, but only (Z)‐3‐hexenol and BZN did so to a level not significantly different from the Ph:5VB blend. Aromatics had a stronger effect than green leaf volatiles (GLVs), because their removal, but not the removal of GLVs, decreased landing responses. The addition of the 5VB decreased significantly the time males needed to reach the odour source. The observed enhanced male attraction to mixtures of pheromone and plant volatiles will facilitate the development of lures for G. molesta adult flight monitoring.

Genetics of sex pheromone blend differences between Heliothis virescens and Heliothis subflexa: a chromosome mapping approach.

Males of the noctuid moths, Heliothis virescens and H. subflexa locate mates based on species‐specific responses to female‐emitted pheromones that are composed of distinct blends of volatile compounds. We conducted genetic crosses between these two species and used AFLP marker‐based mapping of backcross families (H. subflexa direction) to determine which of the 30 autosomes in these moths contained quantitative trait loci (QTL) controlling the proportion of specific chemical components in the pheromone blends. Presence/absence of single H. virescens chromosomes accounted for 7–34% of the phenotypic variation among backcross females in seven pheromone components. For a set of three similar 16‐carbon acetates, two H. virescens chromosomes interacted in determining their relative amounts within the pheromone gland and together accounted for 53% of the phenotypic variance. Our results are discussed relative to theories about population genetic processes and biochemical mechanisms involved in the evolution of new sexual communication systems.

Mating-induced differential coding of plant odour and sex pheromone in a male moth

Innate behaviours in animals can be influenced by several factors, such as the environment, experience, or physiological status. This behavioural plasticity originates from changes in the underlying neuronal substrate. A well‐described form of plasticity is induced by mating. In both vertebrates and invertebrates, males experience a post‐ejaculatory refractory period, during which they avoid new females. In the male moth Agrotis ipsilon, mating induces a transient inhibition of responses to the female‐produced sex pheromone. To understand the neural bases of this inhibition and its possible odour specificity, we carried out a detailed analysis of the response characteristics of the different neuron types from the periphery to the central level. We examined the response patterns of pheromone‐sensitive and plant volatile‐sensitive neurons in virgin and mated male moths. By using intracellular recordings, we showed that mating changes the response characteristics of pheromone‐sensitive antennal lobe (AL) neurons, and thus decreases their sensitivity to sex pheromone. Individual olfactory receptor neuron (ORN) recordings and calcium imaging experiments indicated that pheromone sensory input remains constant. On the other hand, calcium responses to non‐pheromonal odours (plant volatiles) increased after mating, as reflected by increased firing frequencies of plant‐sensitive AL neurons, although ORN responses to heptanal remained unchanged. We suggest that differential processing of pheromone and plant odours allows mated males to transiently block their central pheromone detection system, and increase non‐pheromonal odour detection in order to efficiently locate food sources.

Periodical and Age-related Variation in Chemical Communication System of Black Cutworm Moth, Agrotis ipsilon

Periodical and age-related changes in sex pheromone signaling and response were studied in the black cutworm moth, Agrotis ipsilon. Females began to call on the first night after eclosion and called mainly during the second half of the scotophase. The percentage of females calling increased from 1- to 3-day-old females and decreased from 3- to 6-day-old females (P < 0.001). One-day-old females called later in the scotophase than 2- and 3-day-old females (P = 0.016). The quantity of Z7–12:Ac, Z9–14:Ac, and Z11–16:Ac in pheromone gland extracts of 1- to 6-day-old females varied with time of the photoregime, increasing during scotophase and decreasing during photophase (P ≤ 0.001). These oscillations were described by using equations containing angular terms with a period of 24 hr. The quantities of Z7–12:Ac and Z9–14:Ac, but not of Z11–16:Ac, varied with female age during the calling period (P < 0.001, P = 0.021, and P = 0.529, respectively). The ratios of Z9–14:Ac and Z11–16:Ac to Z7–12:Ac did not change with age or time during calling period. Male response to female pheromone in a wind tunnel increased with age and time of the scotophase. The type of response exhibited by the males (taking flight, oriented flight, and pheromone source contact) was affected by both age and time of the scotophase (P < 0.001).

Day-Night and Phenological Variation of Apple Tree Volatiles and Electroantennogram Responses in Cydia pomonella (Lepidoptera: Tortricidae)

Abstract Volatile compounds from apple trees (variety Golden Smothee) were collected in the field from attached apple branches enclosed in plastic bags in the morning and at dusk and during three growth periods (after petal fall [APF], immature fruit [IF], and close-to-full ripening [CFR]). Collections were analyzed by gas chromatography–mass spectrometry (GC-MS) and gas chromatography–electroantennographic detection (GC-EAD) using the antennae of Cydia pomonella males as biological detectors. Forty-four compounds were detected in the volatile collections. The most abundant compound in all treatments was (Z)-3-hexenyl acetate, a common green leaf volatile. Other abundant compounds were (Z)-3-hexenol, (E,E)-α-farnesene, hexyl acetate, 4,8-dimethyl-1,3,7-nonatriene, hexyl hexanoate, and germacrene D. Most of the compounds that showed significant differences between periods were emitted in greater amounts in the APF and/or IF periods than in the CFR period. (E)-β-caryophyllene and an unidentified compound were significantly more abundant during the day, whereas 2-hexanone, octanal, and (Z)-3-hexenol were significantly more abundant at dusk. GC-EAD responses were very weak and significantly higher than background noise only to hexyl acetate, 4,8-dimethyl-1,3,7-nonatriene, nonanal, (Z)-3-hexenol, hexyl butanoate, and (E,E)-α-farnesene. In further electroantennographic (EAG) assays with synthetic compounds, high responses by the antennae of both males and females were recorded to many of the compounds identified. Males showed a response equal to or higher than females to all compounds except β-myrcene.

Chemical and behavioral evidence for a third pheromone component in a North American population of the black cutworm moth, Agrotis ipsilon

The sex pheromone of Agrotis ipsilon had been previously identified as a blend of (Z)-7-dodecenyl acetate (Z7–12:Ac) and (Z)-9-tetradecenyl acetate (Z9–14:Ac). A synthetic blend of Z7–12:Ac and Z9–14:Ac (30 μg:10 μg) is effective in attracting males in the field. In several countries, addition of (Z)-11-hexadecenyl acetate (Z11–16:Ac) to the previously identified blend increases male captures, but this had not been demonstrated in North America. We found Z11–16:Ac, in addition to Z7–12:Ac and Z9–14:Ac, from pheromone gland extracts of females from North America. The mean ratio of Z7–12:Ac, Z9–14:Ac, and Z11–16:Ac produced by individual females was 70.5:14.2:15.3, respectively. In Kentucky, addition of Z11–16:Ac (60 μg) to a two-component blend of Z7–12:Ac and Z9–14:Ac significantly increased the trap capture rate in the field. Traps baited with this three-component blend were 3.3 times (1995) and 4.6 times (1996) more effective in capturing male A. ipsilon than the two-component blend. This improved effectiveness resulted in detection of A. ipsilon in 60% more of the sampling periods in the two years. In the wind tunnel, males flew upwind and contacted a rubber septum loaded with a three-component blend including Z11–16:Ac significantly more frequently than they did to any two-component blend. These results demonstrate that Z11–16:Ac is a pheromone component in this North American population of A. ipsilon.

Aggressive Chemical Mimicry by the Bolas Spider Mastophora hutchinsoni: Identification and Quantification of a Major Prey's Sex Pheromone Components in the Spider's Volatile Emissions

The adult female bolas spider Mastophora hutchinsoni feeds exclusively on attracted males of a few moth species. This exclusivity and the behavior of the approaching moths suggest that the spider aggressively mimics the sex pheromones of its prey species. Males of the bristly cutworm, Lacinipolia renigera, are a major prey of this spider, accounting for about two thirds of the biomass of prey consumed. Female bristly cutworms produce a pheromone blend consisting of (Z)-9-tetradecenyl acetate (Z9–14 : Ac) and (Z,E)-9,12-tetradecenyl acetate (ZE-9,12–14 : Ac). To determine if M. hutchinsoni females mimic the sex pheromone components and blend ratio of L. renigera, we collected volatiles from hunting adult female spiders and analyzed them with gas chromatography–electroantennographic detection (GC-EAD) and gas chromatography–mass spectrometry (GC-MS). GC-EAD analysis of volatile collections, using a male bristly cutworm antenna as the detector and two capillary columns of different polarities, revealed the presence of peaks with retention times (Rts) identical to Z9–14 : Ac and ZE-9,12– 14 : Ac. The mass spectrum of a peak with Rt of Z9–14 : Ac was identical to the mass spectrum of the synthetic equivalent. There was an insufficient quantity of the compound with Rt of ZE-9,12–14 : Ac to get a full spectrum, but selective detection of ions at m/z 61 and 192 at the correct Rt supported the identification. On average, the blend collected from spiders contained 54.8 ± 20.8 (SE) pg/min of Z9–14 : Ac and 2.5 ± 1.7 (SE) pg/min of ZE-9,12–14 : Ac. The latter, on average, comprised 2.6 ± 0.7% of the total, which is similar to the blend ratio emitted by bristly cutworm females. Our results indicate that the adult female M. hutchinsoni produces an allomone blend that mimics not only the composition, but also the blend ratio, of the sex pheromone of a major prey species.

Pheromone Blend Variation and Cross-Attraction Among Populations of the Black Cutworm Moth (Lepidoptera: Noctuidae)

Abstract Sex pheromone quantity, blend ratio, and cross-attraction were studied in four populations of the black cutworm, Agrotis ipsilon (Hufnagel). Analysis of pheromone gland extracts showed that the three pheromone components of A. ipsilon, (Z)-7-dodecenyl acetate (Z7–12:Ac), (Z)-9-tetradecenyl acetate (Z9–14:Ac) and (Z)-11-hexadecenyl acetate (Z11–16:Ac) were present in all four populations. On average, Z7–12:Ac was the most abundant component in the populations from Kentucky and Kansas, whereas in the Egyptian and French populations Z11–16:Ac was the most abundant component. All populations had a similar quantity of Z7–12:Ac. The population from Kentucky had significantly more Z9–14:Ac than the population from Kansas, and the other two populations had intermediate quantities of this component (P < 0.05). The Egyptian population had significantly more Z11–16:Ac than the French population, which had significantly more than the populations from Kentucky and Kansas (P < 0.05). Comparing Nearctic (Kentucky and Kansas) versus Palearctic (Egypt and France) populations showed significant differences in the quantity of Z11–16:Ac and in the ratio of Z11–16:Ac to Z7–12:Ac (P < 0.01). Full-sib analysis revealed significant heritabilities in pheromone components and blend ratios in two of the populations. Cross-attraction between individuals from Kansas and from each of the other three populations was tested in paired experiments in a wind tunnel using live females as the source of pheromone. Males did not discriminate between females from their own population and females from the reference population. Thus, significant differences in pheromone blend among geographically distant populations of A. ipsilon did not prevent cross-attraction under laboratory conditions.