Host Location Behavior Research Articles

Phloem-feeding insects create parasitoid-free space for caterpillars

Seemingly small ecological changes can have large, ramifying effects that defy expectations. Such are keystone effects in ecosystems. Phloem-feeding insect herbivores can act as keystone species by altering community structure and species interactions via plant-mediated or ant-mediated mechanisms. Plant responses triggered by phloem feeders can disrupt tri-trophic interactions induced by leaf-chewing herbivores, while ants that tend phloem feeders can deter or prey on other arthropods. Here, we investigate how phloem-feeding herbivores change caterpillar-parasitoid interactions on Quercus alba (white oak) trees in natural forests. We factorially manipulated the presence of phloem-feeding insects as well as ant access on Q.alba branches over multiple years and sites and measured parasitism rates of co-occurring caterpillars. While 19.3% of caterpillars were parasitized when phloem feeders were removed, the presence of phloem feeders completely suppressed parasitism of caterpillars (0%). This stark pattern was consistent across the diverse community of phloem feeders and caterpillars. Our manipulation of ant access had no effect on parasitism of caterpillars, implicating a plant-mediated mechanism. We further assessed the mechanistic hypothesis that phloem feeders suppress plant emission of caterpillar-induced volatile compounds, which could disrupt host-location behavior by parasitoids of caterpillars. Phloem feeders indeed reduced concentrations of four volatile compounds, consistent with the putative plant volatile-mediated mechanism. Given the important role of parasitoids in controlling herbivore populations, this keystone effect of phloem feeders offers novel insight into community dynamics in forests and potentially other terrestrial ecosystems.

Aphid alarm pheromone mimicry in transgenic Chrysanthemum morifolium: insights into the potential of (E)-β-farnesene for aphid resistance.

(E)-β-Farnesene (EBF) serves as the primary component of the alarm pheromone used by most aphid pest species. Pyrethrum (Tanacetum cinerariifolium) exhibits tissue-specific regulation of EBF accumulation and release, effectively mimicking the aphid alarm signal, deterring aphid attacks while attracting aphid predators. However, cultivated chrysanthemum (Chrysanthemum morifolium), a popular and economically significant flower, is highly vulnerable to aphid infestations. In this study, we investigated the high expression of the pyrethrum EBF synthase (TcEbFS) gene promoter in the flower head and stem, particularly in the parenchyma cells. Subsequently, we introduced the TcEbFS gene, under the control of its native promoter, into cultivated chrysanthemum. This genetic modification led to increased EBF accumulation in the flower stem and young flower bud, which are the most susceptible tissues to aphid attacks. Analysis revealed that aphids feeding on transgenic chrysanthemum exhibited prolonged probing times and extended salivation durations during the phloem phase, indicating that EBF in the cortex cells hindered their host-location behavior. Interestingly, the heightened emission of EBF was only observed in transgenic chrysanthemum flowers after mechanical damage. Furthermore, we explored the potential of this transgenic chrysanthemum for aphid resistance by comparing the spatial distribution and storage of terpene volatiles in different organs and tissues of pyrethrum and chrysanthemum. This study provides valuable insights into future trials aiming for a more accurate replication of alarm pheromone release in plants. It highlights the complexities of utilizing EBF for aphid resistance in cultivated chrysanthemum and calls for further investigations to enhance our understanding of this defense mechanism.

Chemical cues involved in the host foraging behavior of Psyttalia concolor wasps to locate the olive fruit fly Bactrocera oleae

Foraging parasitoids rely on infochemicals, derived from the habitat, host plant and/or host insect itself. Here, we studied the olive fruit fly Bactrocera oleae (Rossi) (Diptera: Tephritidae), a major pest in olive agroecosystem and its larval parasitoid, Psyttalia concolor (Szépligeti) (Hymenoptera: Braconidae), a well-established and abundant wasp in Crete. To improve parasitoid’s efficiency as biological control agent, more knowledge on its host location behavior is required. The aim of this study was to investigate the role of oviposition- (OIPVs) and herbivore-induced plant volatiles (HIPVs) emitted by olive trees upon infestation by B. oleae as well as cues emitted by B. oleae, e.g., pheromones, therein. We conducted two-choice bioassays to test the preference of P. concolor to different olfactory stimuli. Moreover, we collected headspace volatiles from olive fruits and branches to investigate whether egg or larval infestation changes volatile emissions locally or/and systemically. We found that P. concolor wasps showed a strong preference to volatiles of B. oleae larval-infested fruits (HIPVs) compared to clean air, non-infested, egg-infested, and mechanical-damaged fruits. But they were not able to discriminate between volatiles of non-infested and larval-infested branches. In addition, the wasps were attracted to cues emitted from the virgin and mated B. oleae females. They were neither attracted to cues emitted by the virgin and mated males nor to the olive fruits with or without the cues of the oviposition marking of the B. oleae. We found important qualitative differences in volatile profiles of egg- and larval-infested fruits: nineteen volatile compounds were only detected in infested fruits, such as the terpenoids (E)-β-ocimene and (E,E)-α-farnesene. Moreover, volatile analysis showed that olives change volatile emissions locally and systemically in response to larval infestation. Our results suggest that both HIPVs and host cues play an important role to P. concolor during host location. Further knowledge on the chemical compounds utilized by the parasitoid to locate infested fruits could help application in olive orchards and to improve the control of the olive fruit fly by natural enemies.

Alterations in the odor profile of plants in cultivar mixtures affect aphid host-location behavior.

The effect of cultivar mixtures on aphid control is attributed to the masking or alteration of host-preferred cultivar odor cues. However, the underlying physiological mechanism remains unclear. This study assessed alterations in the volatile emissions of wheat cultivars grown together (Florence-Aurora and Forment; Florence-Aurora and Montcada) and the consequences for the olfactory preference of aphids. Volatile organic compounds were collected from wheat plants grown in a laboratory under mixed or monoculture conditions and subsequently analyzed. The odor profiles of Florence-Aurora and Montcada were indistinguishable from each other. However, the odors of Florence-Aurora and Forment grown in monocultures differed significantly from those emitted by their mixture. The Florence-Aurora and Forment mixture induced plant physiological responses that affected the emission of single volatile compounds and, consequently, altered volatile organic compound ratios. English grain aphids (Sitobion avenae) were less attracted to the odors of Florence-Aurora and Forment when grown as a mixture than the combination of the odors from Florence-Aurora and Forment monocultures. Moreover, aphids preferred clean air over the odor from the Florence-Aurora and Forment mixture but preferred the odor from the Florence-Aurora and Montcada mixture over clean air. This study highlights the beneficial effects of intraspecific plant diversity on aphid control by altering plant odors in response to plant-plant interactions. The emission of less attractive odor cues consequently affects plant-aphid interactions; hence, less attractive odors are likely to impair aphid host-locating behavior. This effect was exclusive to certain cultivar mixtures, which supports the "right neighbor" concept.

A Review of the Host Plant Location and Recognition Mechanisms of Asian Longhorn Beetle.

The Asian longhorn beetle (ALB), Anoplophora glabripennis Motschulsky, is a polyphagous xylophage with dozens of reported host tree species. However, the mechanisms by which individuals locate and recognize host plants are still unknown. We summarize the current knowledge of the host plant list, host kairomones, odorant-binding proteins (OBPs) and microbial symbionts of this beetle and their practical applications, and finally discuss the host localization and recognition mechanisms. A total of 209 species (or cultivars) were reported as ALB host plants, including 101 species of higher sensitivity; host kairomones were preferentially bound to ALB recombinant OBPs, including cis-3-hexen-1-ol, δ-3-carene, nonanal, linalool, and β-caryophyllene. In addition, microbial symbionts may help ALB degrade their host. Complementarity of tree species with different levels of resistance may reduce damage, but trapping effectiveness for adults was limited using a combination of host kairomones and sex pheromones in the field. Therefore, we discuss host location behavior from a new perspective and show that multiple cues are used by ALB to locate and recognize host plants. Further research into host resistance mechanisms and visual signal recognition, and the interaction of sex pheromone synthesis, symbiont microbiota, and host plants may help reveal the host recognition mechanisms of ALBs.

Intraspecific plant variation and nonhost herbivores affect parasitoid host location behaviour

Parasitoids need to find their hosts in patchy environments that differ in profitability. To maximize foraging efficiency, parasitoids use volatile information of plants on which their hosts feed. The blend of plant volatiles emitted is affected by genetic variation in plants and by the herbivore species feeding on the plant. How parasitoids deal with variation in plant volatiles induced by host or nonhost herbivores on various plant genotypes in a plant stand is unclear. In a wind tunnel, we examined foraging behaviour of the parasitoid Cotesia glomerata in mixes of white cabbage cultivars with host ( Pieris brassicae ) and nonhost herbivores ( Mamestra brassicae or Delia radicum ). We specifically studied the efficiency of parasitoids in locating a host-infested plant when having to pass three other plants that varied in volatile emission by cultivar and herbivore identity. We show that foraging decisions of C. glomerata are affected by the apparency of volatile cues from upwind host-infested plants. We found that parasitoids flew over the first three plants more often when the last plant was a host-infested attractive cultivar and the first three plants were a less attractive cultivar, regardless of the presence of host or nonhost herbivores. Furthermore, parasitoids spent more time on the first three plants if these were infested with host or nonhost larvae, and this effect was stronger when the first three plants were of the attractive cultivar. Our results suggest that parasitoids may more easily locate host herbivores on plant genotypes with more apparent volatile information. However, host location efficiency is affected by the contrast with other plumes of plant volatiles derived from genotypic variation in plants and induction of volatiles by nonhost herbivores. Apparency of information on upwind patches influences patch residence time and patch choice and is an important component of optimal foraging in parasitoids. • Foraging decisions by Cotesia glomerata are affected by the apparency of information. • Profitability of upwind patches affects foraging decisions on the current patch. • Nonhost herbivores with traits similar to the host reduced host location efficiency. • Established parasitoid cultivar preferences are nuanced in complex plant mixtures.

Fine Structure and Distribution of Antennal Sensilla of the Predatory Clerid Beetle, Thanasimus lewisi (Coleoptera: Cleridae)

The predatory clerid beetle Thanasimus lewisi (Jacobson) (Coleoptera: Cleridae) is an important predator of bark beetles (Scolytidae) and has been used in China for the biological control of the larch bark beetle Ips subelongatus Motschulsky and the spruce bark beetle Ips typographus Linnaeus. In this study, the number, external morphology and distribution of antennal sensilla of T. lewisi were determined using scanning electron microscopy. The filiform antennae of both sexes of both species consist of the scape, pedicel, and nine flagellomeres. Two types of sensilla chaetica (SC1 and SC2), four types of sensilla basiconica (SB1, SB2, SB3 and SB4), two types of sensilla trichodea (ST1 and ST2), and Böhm's bristles (BB) were identified according to the morphology and fine structure of each type of sensilla in both sexes. No difference in shape, structure, sensilla distribution and typology was observed between the sexes. The density of sensilla was greater on the last 3 than on the first 8 segments. SC1, SC2, ST1 and ST2 occurred on all antennal segments in both sexes. SB1, SB2 and SB3 were absent on the first 4 segments of the antennae in both sexes. SB4 were found only on the last 2 segments of the antennae. BB only occurred on the scape and pedicel. The distal antennal sensilla of T. lewisi had notably more sensilla than proximal ones in type and number, indicating this is the main area to detect environmental stimuli for feeding or oviposition. These structures likely have roles in the host locating and habitat searching behavior of adult T. lewisi and suggest future studies on the olfaction and host location behavior of T. lewisi and other coleopteran predators.

Nitrogen and plant pathogens alter rice plant volatiles mediating host location behavior of Nilaparvata lugens and its parasitoid Anagrus nilaparvatae

Nitrogen and plant pathogens alter rice plant volatiles mediating host location behavior of Nilaparvata lugens and its parasitoid Anagrus nilaparvatae

External morphology of antennae sensilla on silver leaf whitefly, Bemisia Tabaci, (Hemiptera: Aleyrodidae)

The silverleaf whitefly, Bemisia tabaci, (Gennadius), is an invasive pest causing significant damages to a wide range of crops around the world. In this study, the external morphology and distribution of sensilla on the antennal flagella of adult male and female B. tabaci, was studied using scanning electron microscopy (SEM). Five types of sensory organs were recognized in both sexes, of B. tabaci; microtrichia sensilla, basiconic sensilla, grooved surface trichodea sensilla, chaetae sensilla, coeloconic sensilla, and finger-like sensilla. Four coeloconic sensilla, were observed on the antenna sub-segments, two in the first sub-segment, one in the third sub-segment, and one in the fifth sub-segment. basiconic sensilla (BS) were present on the antenna sub-segments of both sexes as single BS in the first, fourth, and fifth sub-segments with deep lengthwise grooves. In contrast, chaetae sensilla were found exclusively on the pedicel in both sexes. Although the types, and the distribution numbers of sensilla antennae of males and female were basically similar, major differences were recorded between the sexes in length of the antennae, whereas females have greater longer of the antennae than males. These results would be helpful for further studies on detailed in the host location behavior of B. tabaci.

Host seed type and volatile compound abundance level mould host location and preference behaviours in Callosobruchus maculatus (Fabricius, 1775) (Coleoptera: Chrysomelidae)

Dry seeds of cowpea, an important food, and cash crop to farmers, are heavily infested by Callosobruchus maculatus (Fabricius, 1775) during storage, causing huge economic loss. As a result, farmers spray pesticides on their harvest to control the pest attack with little consideration for the consequences of their actions. Due to health and environmental concerns associated with pesticide applications, farmers, marketers, and end-users are seeking alternative safer routes to handling this infestation problem. Thus, this study investigated the response of mated female C. maculatus to odour cues from different bean types using two-arm and four-arm olfactometers. The volatile organic compounds from the preferred beans (Borno brown and black-eyed beans-cultivars of Vigna unguiculata Walper, 1843 and adzuki bean – Vigna angularis (Willdenow) Ohwi & Ohashi, 1969), were analysed using gas chromatography-mass spectrometry (GCMS) techniques and headspace volatile organic compounds were tested in 2-arm olfactometer with the view to identifying possible attractants or deterrents that could be used in effective control of storage pest. The results indicated that (a) the female C. maculatus responded discriminatorily to odour stimuli from the bean types tested, (b) eighteen volatile compounds were present in the bean types tested and (c) the volatile compounds identified varied in abundance profile. These suggest that host location and selection behaviours by female C. maculatus are moulded by the types and concentrations of the volatile compounds present in the beans.

Old Parasitoids for New Mealybugs: Host Location Behavior and Parasitization Efficacy of Anagyrus vladimiri on Pseudococcus comstocki.

Simple SummaryAnagyrus vladimiri has been widely employed as a biological control agent (BCA) against the vine mealybugs Planococcus ficus but the knowledge about its employment against other mealybug species is limited. In this study, we investigated the potential efficacy of A. vladimiri for Pseudococcus comstocki management, considering the increasing threat represented by this mealybug pest in Mediterranean vineyards and fruit orchards. No-choice and two-choice tests were conducted to quantify parasitoid behavior against P. ficus and P. comstocki. Our results pointed out that A. vladimiri successfully parasitized both pests, showing no host preference between the two species. Our observations highlight that this parasitoid can be successfully deployed as BCA against P. comstocki populations.The Comstock mealybug, Pseudococcus comstocki (Hemiptera: Pseudococcidae) is a primary pest of orchards in the North and Northwest of China. This pest appeared recently in Europe, including Italy, where it is infesting mainly vineyards as well as apple and pear orchards. The present study investigated the efficacy of Anagyrus vladimiri, a known biological control agent (BCA) of Planococcus ficus, on P. comstocki to evaluate a potential use for the management of this new pest. No-choice tests were conducted to quantify the parasitoid behavior against P. ficus and P. comstocki. The parasitoid successfully parasitized both species (parasitization rate: 51% and 67% on P. comstocki and P. ficus, respectively). The A. vladimiri developmental time (19.67 ± 1.12 vs. 19.70 ± 1.07 days), sex ratio (1.16 ± 1.12 vs. 1.58 ± 1.07) and hind tibia length of the progeny showed no differences when P. comstocki and P. ficus, respectively, were exploited as hosts. Two-choice tests, conducted by providing the parasitoid with a mixed population of P. ficus and P. comstocki, showed no host preference for either of the two mealybug species (23 vs. 27 first choices on P. comstocki and P. ficus, respectively). The parasitization rate (61.5% and 64.5% in P. comstocki and P. ficus, respectively) did not differ between the two hosts. Overall, our study adds basic knowledge on parasitoid behavior and host preferences and confirms the use of this economically important encyrtid species as an effective BCA against the invasive Comstock mealybug.

The presence of knockdown resistance mutations reduces male mating competitiveness in the major arbovirus vector, Aedes aegypti.

The development of insecticide resistance in mosquitoes can have pleiotropic effects on key behaviours such as mating competition and host-location. Documenting these effects is crucial for understanding the dynamics and costs of insecticide resistance and may give researchers an evidence base for promoting vector control programs that aim to restore or conserve insecticide susceptibility. We evaluated changes in behaviour in a backcrossed strain of Aedes aegypti, homozygous for two knockdown resistance (kdr) mutations (V1016G and S989P) isolated in an otherwise fully susceptible genetic background. We compared biting activity, host location behaviours, wing beat frequency (WBF) and mating competition between the backcrossed strain, and the fully susceptible and resistant parental strains from which it was derived. The presence of the homozygous kdr mutations did not have significant effects on blood avidity, the time to locate a host, or WBF in females. There was, however, a significant reduction in mean WBF in males and a significant reduction in estimated male mating success (17.3%), associated with the isolated kdr genotype. Our results demonstrate a cost of insecticide resistance associated with an isolated kdr genotype and manifest as a reduction in male mating success. While there was no recorded difference in WBF between the females of our strains, the significant reduction in male WBF recorded in our backcrossed strain might contribute to mate-recognition and mating disruption. These consequences of resistance evolution, especially when combined with other pleiotropic fitness costs that have been previously described, may encourage reversion to susceptibility in the absence of insecticide selection pressures. This offers justification for the implementation of insecticide resistance management strategies based on the rotation or alternation of different insecticide classes in space and time.

Involvement of chemosensory proteins in host plant searching in the bird cherry-oat aphid.

Chemosensory systems are considered to play an important role in host plant selection in herbivorous insects. However, few studies have focused on chemosensory proteins (CSPs) for aphid host-location mechanisms. The roles of CSPs in searching for different Poaceae species (wheat, barley, triticale, maize and sorghum) were tested in Rhopalosiphum padi, an important cereal pest. The olfactometer assays showed that R. padi responds to plant odors. Seven R. padi CSP genes were identified. Influence of aphid morph, tissue and starvation state on expression patterns of CSPs was evaluated. Expression levels of CSP1, CSP4, CSP5 and CSP6 in winged aphids were significantly higher than those in wingless ones. Transcription levels of four genes (CSP1, CSP4, CSP5 and CSP6) were relatively higher in the head with antennae, and the four genes tended to be upregulated following starvation. Silencing of three CSPs (CSP4, CSP5 and CSP6) altered aphid host-location behavior in response to the five different host plants tested. Three volatile compounds of host plants (octanal, [E]-2-hexenol and linalool) have significant attraction to winged R. padi according to the four-arm olfactometer tests. Molecular docking predicted hydrogen bonding sites which played key roles in the binding of CSP4, CSP5 and CSP6 with volatile compounds. Knockdown of CSP4 or CSP5 significantly decreased the staying time of R. padi in the arms with octanal. However, knockdown of CSP6 could not affect the response of R. padi to octanal. These results bring evidence for the involvement of three CSPs in R. padi host-location behavior.

Essential oils of Tagetes minuta and Tithonia diversifolia affect host location behaviour and on-host attachment site preference of the brown ear tick, Rhipicephalus appendiculatus in the semi-field studies

Effects of essential oils of Tagetes minuta and Tithonia diversifolia (Asteraceae) on orientation behaviour and on-host attachment site preference of newly hatched adult Rhipicephalus appendiculatus were evaluated. Host animals were treated at the ear pinna (by smearing the oil directly on the ear or suspending a tube containing the oil on the ear pinna) and legs + tail in semi-field plots. The legs + tail sites of the essential oil application showed the lowest mean percentage of ticks observed on host body (16.5 ± 1.9% and 26.0 ± 2.8%) and the highest mean percentage reduction of attaching ticks (76.5 ± 3.9% and 67.0 ± 0.8%) for essential oils of Tagetes minuta and Tithonia diversifolia, respectively. The control animals had the highest mean percentage of ticks observed (93.0 ± 2.1%). The ear tube resulted in the highest mean percentage of ticks on the host (47.5 ± 5.1% and 55.8 ± 5.1%) and a lowest mean percentage reduction of attaching ticks (44.8 ± 5.1% and 36.5 ± 7.4%) for the essential oils of Tagetes minuta and Tithonia diversifolia, respectively. For both the essential oils, legs + tail sites of essential oil application, followed by ear smear and then ear tube, had significant effects on orientation to the host and attachment site preference of adult R. appendiculatus on the host, in that order. We, therefore, recommend the ear smear site for treating hosts with essential oils whose performance may improve upon increasing concentration and formulating them in a carrier material that stabilizes the active ingredients.

Intercropping impacts the host location behaviour and population growth of aphids

AbstractIncreasing intrafield plant diversity has been shown to regulate pest populations in various agroecosystems. Among the suggested mechanisms for this bottom‐up pest control, the disruptive crop hypothesis states that herbivores' abilities to locate and colonize their host plants are reduced by the presence of non‐host plants. Under laboratory conditions, we evaluated how intercropping wheat and legumes modifies the behaviour of apterous cereal aphids,Sitobion avenae(Fabricius) (Hemiptera: Aphididae), in terms of host plant location and population growth. We compared two intercropping systems – soft winter wheat,Triticum aestivumL. (Poaceae), associated with winter pea,Pisum sativumL., or with white clover,Trifolium repensL. (both Fabaceae) – and sole stands of soft winter wheat. Aphids needed more time to locate their wheat host plant and then spent less time on wheat when it was intercropped with clover. At the population level, and accounting for host plant biomass, only intercropping wheat with clover significantly reduced aphid densities on wheat, as this was particularly disruptive toS. avenaebehaviour and population growth.Our laboratory study points out that the species used as non‐host plants and their density are important parameters that should be taken into account in field studies on intercropping systems.

Comparison of thermal performances of two Asian larval parasitoids of Drosophila suzukii

Ganaspis brasiliensis Ihering and Leptopilina japonica Novković & Kimura (Hymenoptera: Figitidae) are candidates for biological control of the spotted wing drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilae), an invasive pest originally from East Asia. Developmental time and offspring survival from egg to adult, and fecundity (measured as adult offspring production/female wasp) of a Chinese and a South Korean population of both species were assessed at different constant temperatures. Development time decreased with increasing temperature from 17.2 to 27.5 °C; at 29.3 °C no parasitoid completed development. Temperatures below 17.2 °C triggered a facultative diapause in both species, and this cold temperature response varied among populations of different origin: South Korean populations of G. brasiliensis and L. japonica entered diapause at 17.2 °C, whereas only a proportion of their Chinese counterparts entered diapause at the same temperature. No significant differences in offspring survival and fecundity were detected between populations in the mid-temperature range. However, fecundity at 15.9 °C was higher for South Korean populations of G. brasiliensis and L. japonica compared with their Chinese counterparts, suggesting that the host location and oviposition behavior of the searching females was less affected by the cold temperature and/or their eggs had better cold hardiness. These variations in response to cold temperatures need to be further investigated and their ecological significance assessed to better understand performance of G. brasiliensis and L. japonica in those invaded regions where control is needed.

Ultrastructure observations on antennal sensilla of Heortia vitessoides the most serious pest of Aquilaria sinensis

Heortia vitessoides is the most serious pest of Aquilaria sinensis,which is an economically important evergreen tree native to China and is the principal source of Chinese agarwood. In severe infestations,the insects completely eat up the leaves of A. sinensis,causing severe economic losses. In a more recent study,we found that the antennal sensilla of adult play important roles in the host location,mating and oviposition of H. vitessoides. Here,the external morphology of the antennal sensilla of H. vitessoides were examined using scanning electron microscopy. The result showed that the antennae of both sexes of H. vitessoides were filiform in shape,which consist of the scape,pedicel and about 64 segments of flagellomeres. Eight morphological sensilla types were recorded in both sexes,including sensilla trichodea,sensilla chaetica,sensilla basiconica,sensilla coeloconica,sensilla styloconica,sensilla auricillica,sensilla squamiformia and böhm bristle. Major differences were recorded in the distribution and quantity of different sensilla types in each segment of antenna. The sensillas are almost confined to the ventral and lateral surfaces rather than the back side of antennae. Antennal flagella contained the most sensilla while the scape and pedicel segments only contained böhm bristles and sensilla squamiformias. Sensilla trichodea Ⅲ were only found on male antennae. These results are discussed in relation to the possible roles of the sensilla types in the host location,mating and oviposition selection behavior of H. vitessoides.

Effects of Volatiles from Clavigralla tomentosicollis Stål. (Hemiptera: Coreidae) Adults on the Host Location Behavior of the Egg Parasitoid Gryon fulviventre (Crawford) (Hymenoptera: Scelionidae).

The egg parasitoid Gryon fulviventre is a potential biological control agent of Clavigralla tomentosicollis, a coreid pod-sucking pest of Vigna unguiculata. The host location behavior of naive parasitoid females was studied using a four-armed olfactometer. Two strains of G. fulviventre parasitoids from Burkina Faso and Benin were exposed to odors provided by healthy and infested pods as well as C. tomentosicollis females and males. The time spent in each odor zone was recorded to determine the preference of parasitoid females. Results show that odors from healthy pods, infested pods, and pest females did not attract the parasitoid. However, a significantly attractive response of both strains of G. fulviventre was recorded in the presence of volatiles from males of C. tomentosicollis. Moreover, experiments testing G. fulviventre females’ behavior when simultaneously exposed to volatiles from cowpea pods (healthy and infested) and increasing numbers of C. tomentosicollis males revealed a significantly higher attraction of parasitoid females of both strains by volatiles from ten males of C. tomentosicollis. The results suggest that the males of the insect pest emit a pheromone used as kairomone by parasitoids to locate their host. The conditions determining this attractiveness at field level and its impact on host-searching efficiency are discussed.

Rh6 gene modulates the visual mechanism of host utilization in fruit fly Bactrocera minax.

Vision plays a critical role in host location and oviposition behavior for herbivorous insects. However, the molecular mechanisms underlying visual regulation in host recognition and oviposition site selection in insects remains unknown. The aim of this study was to explore the key visual genes that are linked to the host plant location of the fruit fly, Bactrocera minax. Using a host specialist fruit fly, B. minax, which lays eggs only into immature green citrus fruit, we undertook behavioral, transcriptomic, and RNAi research to identify the molecular basis for host fruit color recognition. In laboratory and field assays we found that adults prefer green over other colors, and this preference is significantly increased in sexually mature over immature flies. Furthermore, we identified that the Rh6 gene, responsible for green spectral sensitivity, has elevated expression in mature flies over immature flies. RNAi suppression of Rh6 eliminated the preference for green, resulting in a significant decrease in the number of eggs laid by B. minax in green unripe citrus. These results show that the Rh6 gene modulates the visual mechanism of host utilization in B. minax, providing a genetic basis for visual host location in a non-model insect herbivore. © 2018 Society of Chemical Industry.

Antennal Transcriptome Analysis of the Chemosensory Gene Families From Trichoptera and Basal Lepidoptera.

The chemosensory gene families of insects encode proteins that are crucial for host location, mate finding, oviposition, and avoidance behaviors. The insect peripheral chemosensory system comprises odorant receptors (ORs), gustatory receptors (GRs), ionotropic receptors (IRs), odorant binding proteins (OBPs), chemosensory proteins (CSPs), and sensory neuron membrane proteins (SNMPs). These protein families have been identified from a large number of insect species, however, they still remain unidentified from several taxa that could provide important clues to their evolution. These taxa include older lepidopteran lineages and the sister order of Lepidoptera, Trichoptera (caddisflies). Studies of these insects should improve evolutionary analyses of insect chemoreception, and in particular shed light on the origin of certain lepidopteran protein subfamilies. These include the pheromone receptors (PRs) in the “PR clade”, the pheromone binding proteins (PBPs), general odorant binding proteins (GOBPs), and certain presumably Lepidoptera-specific IR subfamilies. Hence, we analyzed antennal transcriptomes from Rhyacophila nubila (Trichoptera), Eriocrania semipurpurella, and Lampronia capitella (representing two old lepidopteran lineages). We report 37 ORs, 17 IRs, 9 GRs, 30 OBPs, 7 CSPs, and 2 SNMPs in R. nubila; 37 ORs, 17 IRs, 3 GRs, 23 OBPs, 14 CSPs, and 2 SNMPs in E. semipurpurella; and 53 ORs, 20 IRs, 5 GRs, 29 OBPs, 17 CSPs, and 3 SNMPs in L. capitella. We identified IR members of the “Lepidoptera-specific” subfamilies IR1 and IR87a also in R. nubila, demonstrating that these IRs also occur in Trichoptera. Members of the GOBP subfamily were only found in the two lepidopterans. ORs grouping within the PR clade, as well as PBPs, were only found in L. capitella, a species that in contrast to R. nubila and E. semipurpurella uses a so-called Type I pheromone similar to the pheromones of most species of the derived Lepidoptera (Ditrysia). Thus, in addition to providing increased coverage for evolutionary analyses of chemoreception in insects, our findings suggest that certain subfamilies of chemosensory genes have evolved in parallel with the transition of sex pheromone types in Lepidoptera. In addition, other chemoreceptor subfamilies show a broader taxonomic occurrence than hitherto acknowledged.