Electrophysiological and behavioral responses to chocolate volatiles in both sexes of the pyralid moths Ephestia cautella and Plodia interpunctella

Electrophysiological and Behavioral Responses of Plodia interpunctella (Hübner) Females to Aldehyde Volatiles from Dried Fruits

Plodia interpunctella (Lepidoptera: Pyraloidea) is a notorious pest of stored grain globally. The dried fruits (Ziziphus jujuba, Malus pumila, and Fragaria ananassa) can strongly attract P. interpunctella. However, specific volatile compounds responsible for such effects have not been identified. Volatiles were analyzed by using headspace solid-phase microextraction (HS-SPME) and chromatography-mass spectrometry (GCMS) techniques. Five aldehyde compounds were selected for electroantennogram (EAG), single sensillum recording (SSR), and behavioral response assays. The three chemicals that elicited the strongest EAG responses to mated females at 100 μg/μL include hexanal (1.13 mV), heptanal (0.92 mV), and octanal (0.73 mV). In SSR experiments, the basiconic sensilla of the antennae responded to these aldehyde compounds. The results of behavioral responses showed that all aldehydes exhibited dose-dependent responses, with hexanal having the highest attractant rate of 74.56%. These compounds have the potential to be used for monitoring P. interpunctella and its integrated management program.

Morphology and distribution of antennal sensilla in the gall midge Gephyraulus lycantha (Diptera: Cecidomyiidae)

The gall midge Gephyraulus lycantha (Diptera: Cecidomyiidae) is a serious gall-forming pest that causes devastating damage in the wolfberry, Lycium barbarum (Solanaceae) in Northwest China. In the present study, the external morphology and ultrastructure of the antennae and the antennal sensilla of G. lycantha were examined by scanning electron microscopy. The results show that the moniliform antenna of G. lycantha consisted of a scape, pedicel, and flagellum, and exhibited obvious sexual dimorphism. The male antennae were significantly longer than those of females. Moreover, male flagellomeres were spheroidal nodes separated by slender internodes, whereas those of females were cylindrical with no obvious internodes. There were sex and individual differences in antennal segment number. Male antennae had 10 - 16 flagellomeres, most of which had 15, while female antennae consisted of 8 - 14 flagellomeres, most of which had 12. Moreover, a pair of antennae in the same individual had different numbers of flagellomeres. Four types of sensilla were observed along the surface of the antennae, including sensilla chaetica, sensilla trichodea, sensilla coeloconica, and sensilla circumfila. Among the types of sensilla, sensilla chaetica were the longest and most prominent sensilla discovered on the antennal flagellum in both sexes. Sensilla trichodea were widely distributed over the antennal surface, including the scape, pedicel, and flagellum. Sensilla coeloconica were categorized into four subtypes: sensilla coeloconica Ⅰ, sensilla coeloconica Ⅱ, sensilla coeloconica Ⅲ, and sensilla coeloconica IV; however, sensilla coeloconica IV was absent in females. Sensilla circumfila were found only on cecidomyiidae insect antennae and were attached to the surface by a series of stalks, forming loops around each flagellomere. The numbers of all four types of sensilla on the male antennal windward side were significantly higher than those on the leeward side. The probable biological functions of these sensilla were discussed herein based on their morphology and ultrastructure. These results provide an important basis for further research on chemical communication and strategies for the control of G. lycantha, and it will be able to serve future group Taxonomy studies (species of cecidomyiidae), providing new taxonomic characters (general ultrastructural morphology, number of sensilla and antennal segments, distribution of different types of setae, types and subtypes sensilla), which varies between species and subspecies.

Volatile and Semi-Volatile Organic Compounds May Help Reduce Pollinator-Prey Overlap in the Carnivorous Plant Drosophyllum lusitanicum (Drosophyllaceae)

Most carnivorous plants show a conspicuous separation between flowers and leaf-traps, which has been interpreted as an adaptive response to minimize pollinator-prey conflicts which will reduce fitness. Here, we used the carnivorous subshrub Drosophyllum lusitanicum (Drosophyllaceae) to explore if and how carnivorous plants with minimal physical separation of flower and trap avoid or reduce a likely conflict of pollinator and prey. We carried out an extensive field survey in the Aljibe Mountains, at the European side of the Strait of Gibraltar, of pollinating and prey insects of D. lusitanicum. We also performed a detailed analysis of flower and leaf volatile and semi-volatile organic compounds (VOCs and SVOCs, respectively) by direct thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) to ascertain whether this species shows different VOC/SVOC profiles in flowers and leaf-traps that might attract pollinators and prey, respectively. Our results show a low overlap between pollinator and prey groups as well as clear differences in the relative abundance of VOCs and SVOCs between flowers and leaf-traps. Coleopterans and hymenopterans were the most represented groups of floral visitors, whereas dipterans were the most diverse group of prey insects. Regarding VOCs and SVOCs, while aldehydes and carboxylic acids presented higher relative contents in leaf-traps, alkanes and plumbagin were the main VOC/SVOC compounds detected in flowers. We conclude that D. lusitanicum, despite its minimal flower-trap separation, does not seem to present a marked pollinator-prey conflict. Differences in the VOCs and SVOCs produced by flowers and leaf-traps may help explain the conspicuous differences between pollinator and prey guilds.

Identification of chemosensory genes from the antennal transcriptome of Indian meal moth Plodia interpunctella

Olfaction plays an indispensable role in mediating insect behavior, such as locating host plants, mating partners, and avoidance of toxins and predators. Olfactory-related proteins are required for olfactory perception of insects. However, very few olfactory-related genes have been reported in Plodia interpunctella up to now. In the present study, we sequenced the antennae transcriptome of P. interpunctella using the next-generation sequencing technology, and identified 117 candidate olfactory-related genes, including 29 odorant-binding proteins (OBPs), 15 chemosensory proteins (CSPs), three sensory neuron membrane proteins (SNMPs), 47 odorant receptors (ORs), 14 ionotropic receptors (IRs) and nine gustatory receptors (GRs). Further analysis of qRT-PCR revealed that nine OBPs, three CSPs, two SNMPs, nine ORs and two GRs were specifically expressed in the male antennae, whereas eight OBPs, six CSPs, one SNMP, 16 ORs, two GRs and seven IRs significantly expressed in the female antennae. Taken together, our results provided useful information for further functional studies on insect genes related to recognition of pheromone and odorant, which might be meaningful targets for pest management.

Field Attraction of Carob Moth to Host Plants and Conspecific Females

The carob moth, Ectomyelois ceratoniae (Zeller; Lepidoptera: Pyralidae), is a devastating pest in high-value crops around the world. An efficient sex pheromone attractant is still missing for the management of this pest, because the major pheromone component is unstable. Host plant volatiles attract herbivore insects and have shown to have good potential to be exploited as alternatives or supplements to sex pheromones. To explore this possibility in carob moth, we assessed the attraction of moths to the volatiles of mature pistachio and different fruit stages of pomegranate, alone and in combination with virgin females, using sticky delta traps in pomegranate orchards of Iran. Traps baited with mature pomegranates, whether uncracked or cracked, infested or uninfested, caught significantly larger numbers of male and both mated and virgin female carob moths than unbaited traps. Traps baited with headspace extract of cracked pomegranate only caught mated females, while mature pistachio only attracted males. Pomegranate flowers, unripe pomegranate, and headspace extract of pistachio did not attract moths. Traps baited with cracked fruit caught more mated females than traps baited with uncracked fruit. Males were attracted similarly to traps baited with cracked-infested pomegranate as to traps baited with virgin females alone. Interestingly, the combination of cracked pomegranate and virgin female enhanced the attraction of virgin females. Together, our results show that volatiles from cracked pomegranates alone or in combination with female sex pheromone have great potential for application in pest management programs of carob moth.

Characterizing the scent and chemical composition of Panthera leo marking fluid using solid-phase microextraction and multidimensional gas chromatography-mass spectrometry-olfactometry

Lions (Panthera leo) use chemical signaling to indicate health, reproductive status, and territorial ownership. To date, no study has reported on both scent and composition of marking fluid (MF) from P. leo. The objectives of this study were to: 1) develop a novel method for simultaneous chemical and scent identification of lion MF in its totality (urine + MF), 2) identify characteristic odorants responsible for the overall scent of MF as perceived by human panelists, and 3) compare the existing library of known odorous compounds characterized as eliciting behaviors in animals in order to understand potential functionality in lion behavior. Solid-phase microextraction and simultaneous chemical-sensory analyses with multidimensional gas-chromatography-mass spectrometry-olfactometry improved separating, isolating, and identifying mixed (MF, urine) compounds versus solvent-based extraction and chemical analyses. 2,5-Dimethylpyrazine, 4-methylphenol, and 3-methylcyclopentanone were isolated and identified as the compounds responsible for the characteristic odor of lion MF. Twenty-eight volatile organic compounds (VOCs) emitted from MF were identified, adding a new list of compounds previously unidentified in lion urine. New chemicals were identified in nine compound groups: ketones, aldehydes, amines, alcohols, aromatics, sulfur-containing compounds, phenyls, phenols, and volatile fatty acids. Twenty-three VOCs are known semiochemicals that are implicated in attraction, reproduction, and alarm-signaling behaviors in other species.

Oviposition by Female Plodia interpunctella (Lepidoptera: Pyralidae): Description and Time Budget Analysis of Behaviors in Laboratory Studies

The oviposition behavior of the Indian meal moth, Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), a major insect pest of durable stored foods, was studied in small experimental arenas under laboratory conditions using videography, and a time budget analysis of its behaviors was documented. Resting gravid females typically became active shortly after the start of the scotophase. The characteristic behaviors exhibited by mated females prior to oviposition included antennal movement, grooming of antennae and mouth parts using the forelegs, walking or flying, and abdomen bending and dragging. Pre-oviposition behaviors such as antennal grooming and walking or flying were observed to alternate several times before females commenced the abdominal dragging behavior that preceded egg laying. Eggs were laid singly or sometimes in groups, either freely or stuck to food material. Gravid females showed little or no movement during the photophase; however, they actively flew and oviposited during the scotophase. Females allocated only a small portion of their time to oviposition while the rest of the time was spent away from food. Females oviposited on food material by making repeated visits, predominantly during the first four hours of the scotophase. Visits and time spent on food declined as the scotophase advanced.

Chopper-stabilized gas chromatography-electroantennography: Part I. background, signal processing and example

A new method that can improve gas-chromatography-electroantennographic detection (GC-EAD) by orders of magnitude through a technique known as chopper stabilization combined with matched filtering in colored noise is presented. The EAD is a physiological recording from the antenna of an insect which can be used to find compounds in the GC effluent that the antenna is able to detect, having important applications for pest control and understanding of chemical communication in nature. The new method is demonstrated with whole-animal male Helicoverpa zea antennal preparations for detection of major pheromone component (cis-11-hexadecenal) and compared to results obtained using traditional EAD recording techniques. Results indicate that chopper stabilization under these circumstances can increase odorant detection performance by a factor of approximately 10(4) over traditional methods. The time course of the response of the antenna is also better resolved under chopped conditions. Although the degree of improvement is expected to vary with insect species, odor, and insect preparation, under most circumstances a more sensitive and robust GC-EAD instrument will result from the application of this technique.

Behavioral responses of adult Sitophilus granarius to individual cereal volatiles

The antennae of Sitophilus granarius (L.) (Coleoptera: Curculionidae) adults detect a wide variety of compounds in the odor blend of various cereal grains (Germinara et al., Tec. Molit., 53:27-34, 2002). In the present study, we looked at the behavioral responses of the granary weevil to 20 of these individual volatiles (aliphatic alcohols, aldehydes, ketones, and aromatics) in a two-choice pitfall olfactometer, using the aggregation pheromone and propionic acid as the attractant and repellent controls, respectively. Five doses, ranging from 1 microg to 1 mg, of each compound were tested. At least one concentration of eight compounds attracted beetles but required doses 1,000- to 5,000-fold higher than the concentration of aggregation pheromone to elicit a response. Three compounds, while attractive at lower concentrations, acted as repellents at higher doses. Twelve compounds were repellent at concentrations similar to the quantity of propionic acid that significantly repelled beetles. The data show that granary weevil adults have the ability to respond behaviorally to a wide range of cereal volatiles and that responses may change as a function of concentration. The results suggest that host finding behavior of weevils will depend on the balance of positive and negative volatile stimuli from grain as the relative concentrations of volatiles may change during storage. An understanding of how the weevils respond to such changes could be useful for the development of effective integrated pest management strategies.

Analysis and Manipulation of the Structure of Odor Plumes from a Piezo-Electric Release System and Measurements of Upwind Flight of Male Almond Moths, Cadra cautella, to Pheromone Plumes

We investigated the plume structure of a piezo-electric sprayer system, set up to release ethanol in a wind tunnel, using a fast response mini-photoionizaton detector. We recorded the plume structure of four different piezo-sprayer configurations: the sprayer alone; with a 1.6-mm steel mesh shield; with a 3.2-mm steel mesh shield; and with a 5 cm circular upwind baffle. We measured a 12 x 12-mm core at the center of the plume, and both a horizontal and vertical cross-section of the plume, all at 100-, 200-, and 400-mm downwind of the odor source. Significant differences in plume structure were found among all configurations in terms of conditional relative mean concentration, intermittency, ratio of peak concentration to conditional mean concentration, and cross-sectional area of the plume. We then measured the flight responses of the almond moth, Cadra cautella, to odor plumes generated with the sprayer alone, and with the upwind baffle piezo-sprayer configuration, releasing a 13:1 ratio of (9Z,12E)-tetradecadienyl acetate and (Z)-9-tetradecenyl acetate diluted in ethanol at release rates of 1, 10, 100, and 1,000 pg/min. For each configuration, differences in pheromone release rate resulted in significant differences in the proportions of moths performing oriented flight and landing behaviors. Additionally, there were apparent differences in the moths' behaviors between the two sprayer configurations, although this requires confirmation with further experiments. This study provides evidence that both pheromone concentration and plume structure affect moth orientation behavior and demonstrates that care is needed when setting up experiments that use a piezo-electric release system to ensure the optimal conditions for behavioral observations.

Synergism and redundancy in a plant volatile blend attracting grapevine moth females

A flight tunnel study was done to decipher the behavioral effect of grape odor in grapevine moth Lobesia botrana. A blend of 10 volatile compounds, which all elicit a strong antennal response, attracts mated grapevine moth females from a distance, by upwind orientation flight. These 10 grape volatiles are in part behaviorally redundant, since attraction to a 3-component blend of beta-caryophyllene, (E)-beta-farnesene and (E)-4,8-dimethyl-1,3,7-nonatriene was not significantly different from the 10-component blend. Blending these three compounds had a strong synergistic effect on female attraction, and omission of any one compound from this 3-component blend almost abolished attraction. It was nonetheless possible to substitute the three compounds with the other grape volatiles which are perceived by the female antenna, to partly restore attraction. Several blends, of varying composition, elicited significant attraction. The observed behavioral plasticity in response to grape volatile blends probably reflects the variation of the natural plant signal, since females oviposit on different grape varieties, in different phenological stages.

Semiochemicals for insect pest management

Methods for crop protection based on semiochemicals show advantages over methods based on conventional insecticides. Applications of semiochemicals for insect pest management have, however, been limited. Some recent studies carried out in an interdisciplinary research program by five research groups in Sweden are presented. In spite of the chemodiversity in nature, it is striking that many simple and common compounds are important as chemical signals. This paper focuses on some examples of such simple signals, which are now used for monitoring and suppression of pest insects.