Oviposition Site Preference Research Articles

The odorant-binding protein genes obp67 and obp56d-like encode products that guide oviposition site selection in the Asian tiger mosquito, Aedes albopictus.

Aedes albopictus is an important vector of arboviruses and prefers small containers of stagnant water as oviposition sites. One of the mechanisms mosquitoes use to search for suitable oviposition sites is relying on odor cues from prospective sites and their surroundings. The genetic and molecular bases of this behavior are not known for Ae.albopictus. Oviposition site-searching behavior can be separated into 2 stages: container location and water detection. We applied a glue compound to the antennae and the maxillary palps of adult females to mask their ability to detect molecules that may guide them to preferred oviposition sites. Treatment of the antennae significantly reduces the location index (P<0.001), indicating a decreased ability to find oviposition sites, whereas no significant difference was observed in mosquitoes with maxillary palps treated with the same glue compound (P>0.05). The detection time, measured as the duration from contact with the water surface to the deposition of the first egg, was extended in mosquitoes with treated antennae or maxillary palps, supporting the conclusion that olfaction is involved in the detection of oviposition site. Transcriptomic analysis identified differentially expressed olfactory-related genes, including obp67, obp56d-like, obp19d-like and obp67-like. RNA interference (RNAi)-mediated knockdown of obp67 and obp56d-like significantly affected the location index and detection time, respectively. Cas9/guide RNA-mediated knockout of obp56d-like resulted in a prolonged detection time, compared with the wild type (P<0.05). These findings help to elucidate aspects of the olfactory mechanisms involved in Ae.albopictus oviposition site selection, and provide a basis for the development of mosquito surveillance and control strategies.

Characteristics of logs with signs of oviposition by the polyphagous xylophage Asian longhorned beetle (Coleoptera: Cerambycidae).

During the eradication program undertaken against Anoplophora glabripennis (Motschulsky) in the Greater Toronto Area, information was collected on the numerous signs of injury found on wounded trees. Herein, we used a portion of this information to assess the characteristics of logs with signs of oviposition (i.e., pits). Specifically, we related the basal diameter, type (log bole vs. log branch), height above ground, and branch hierarchy level of logs with pits to tree size (i.e., height and diameter at breast height) and level of infestation intensity. In general, pits were concentrated on logs from the bole and branches that were 8-14cm in diameter in the lower 8 m of the bole and in the first 2 levels of the branching hierarchy. Oviposition pit location was strongly influenced by tree size-both height and diameter at breast height, with more pits on the lower bole in small trees and then higher on the bole and into the branches as tree size increased. As tree-level infestation intensity increased, pits were found on both larger and smaller diameter portions of the trees, presumably as preferred oviposition sites became saturated. These findings can improve the efficacy of surveillance activities for A. glabripennis.

The oviposition preference and offspring performance of Aethina tumida (Coleoptera: Nitidulidae).

Given the rapid spread and potential harm caused by the small hive beetle, Aethina tumida (Coleoptera: Nitidulidae) in China, it has become imperative to comprehend the developmental biology of this invasive species. Currently, there is limited knowledge regarding the impact of A. tumida female oviposition site preference on larval growth and development. To examine this, we investigated the ovipositional preference of adult female A. tumida on bee pupae, beebread, banana, and honey through a free choice test. Furthermore, we assessed the impact of these food resources on offspring performance, which included larval development time, survival, wandering larvae weight, emerged adult body mass, reproduction, and juvenile hormone titer. Our results showed that A. tumida females exhibited a strong preference for ovipositing on bee pupae compared to other diets, while showing reluctance toward honey. Moreover, A. tumida larvae that were fed on bee pupae displayed accelerated growth compared to those fed on other diets. Furthermore, A. tumida fed on bee pupae exhibited higher weights for wandering larvae, and emerged adult, increased pupation rates, enhanced fecundity and fertility, as well as a larger number of unilateral ovarioles during the larval stage when compared to those fed on other diets. Overall, the results indicate that the oviposition preferences of A. tumida females are adaptive, as their choices can enhance the fitness of their offspring. This finding aligns broadly with the hypothesis of oviposition preference and larval performance. This study can provide a foundation for the development of attractants aimed at promoting the oviposition of the A. tumida adults.

Contrasting responses to microhabitat and temperature determine breeding habitat differentiation between two Viola‐feeding butterflies

Abstract Since widespread monitoring began in 1976 in the UK, habitat‐specialist butterfly populations have declined dramatically. The main driver is habitat degradation, caused primarily by land‐use change, perhaps interacting with changes in vegetation phenology. Here, we focus on two declining species: Boloria selene (Dennis &amp; Schiffermüller) and Boloria euphrosyne L., Lepidoptera: Nymphalidae. We hypothesise that these species differ in their preferred breeding habitat, and this is driven by differences in their temperature preferences, mediated by vegetation cover. We use mark‐release‐recapture techniques and oviposition observations to characterise and compare adult distribution, habitat use and oviposition site preferences of the two species. Egg‐laying females of both species are shown to occur in areas with relatively high abundance of the larval food plants, Viola spp. (violets), principally V. riviniana, and they oviposit where Viola spp. abundance is locally high. However, in contrast to B. selene, ovipositing B. euphrosyne tends to occur in areas with relatively short and sparse cover of vegetation. B. euphrosyne oviposit in sites with a relatively high plant surface temperature irrespective of ambient temperatures, in contrast with B. selene in which the temperature of oviposition sites increases as ambient temperature increases. These differential temperature strategies likely underlie differences in breeding habitat preference. Microclimatic cooling caused by increased vegetation growth in spring may be one reason B. euphrosyne is declining in the UK, while both B. euphrosyne and B. selene may be affected by declining Viola spp. availability. Our data provide further evidence that drivers of butterfly declines can be multi‐factorial, and paradoxically, that thermophilic species do not necessarily benefit from climate warming if responses of other species result in cooling of their habitats.

Effect of acetic acid bacteria colonization on oviposition and feeding site choice in Drosophila suzukii and its related species.

Unlike many species of Drosophila flies that colonize decaying fruits, Drosophila suzukii lay eggs in ripening fruits. The oviposition and feeding site preferences for bacterial growth were quantified in multiple strains of D. suzukii and its closely related species, D. subpulchrella and D. biarmipes . A continuous degree of preference for oviposition sites with Acetobacter growth both within and across species suggested that the separation in resource usage is notable but not complete among these species. The lack of interspecific differences in feeding site preference for Acetobacter -containing media implied that the oviposition site preferences evolved independently from the feeding site preference.

Exploring Life History Choices: Using Temperature and Substrate Type as Interacting Factors for Blowfly Larval and Female Preferences.

Blowflies (Diptera: Calliphoridae) present a wide range of larval lifestyles, typically classified as obligate parasitism, facultative parasitism, and complete sapro-necrophagy. Several parasitic species, both obligate and facultative, are considered to be of sanitary and economic importance, as their larvae can cause myiasis (maggot infestation in live tissue). However, it is noteworthy that the adult female plays a decisive role as she chooses the oviposition site, and, therefore, largely determines the feeding habit and developmental conditions of the larvae. In this study, two protocols are proposed to test larval feeding preference and female oviposition site preference considering two interacting factors: meat substrate type and temperature. The setups presented here allowed to test Lucilia cuprina larvae and gravid females in a four-choice assay with two temperatures (33 ± 2 °C and 25 ± 2 °C) and two types of meat substrates (fresh meat supplemented with blood and 5-day-old rotten meat). Larvae or gravid females can choose to burrow or lay their eggs, respectively, in either of the following: rotten meat at 25 °C (simulating a necrophagous species condition), fresh meat supplemented with blood at 33 °C (simulating a parasitic species condition), and two controls, rotten meat at 33 °C, or fresh meat supplemented with blood at 25 °C. The preference is assessed by counting the number of larvae or eggs laid in each option for each replicate. Comparing the observed results to a random distribution allowed for the estimation of the statistical significance of the preference. The results indicated that L. cuprina larvae have a strong preference for the rotten substrate at 25 °C. Conversely, oviposition-site preference by females was more varied for the meat type. This methodology can be adapted to test the preference of other insect species of similar size. Other questions can also be explored by using alternative conditions.

Alkaline water as a potential agent for biting midge control: Managing effectiveness and non-target organism impact evaluation.

Biting midge Forcipomyia taiwana is one of the common pests in East Asia. Their nuisance and blood-sucking behavior causes problems not only for human health but also for some industries. This study aims to evaluate the effectiveness of spraying alkaline water on controlling biting midge population and potential side effects of such approach on non-target organisms. Laboratory experiments were conducted to evaluate the effect of alkaline water on oviposition site preference of female biting midges as well as crickets. Effect of alkaline water on distribution pattern of earthworms was also examined. Besides, we also performed field manipulative studies by long term spraying of alkaline water to evaluate the effects on biting midge density, microalgae abundance and ground arthropod communities. The results of laboratory experiments showed that female biting midges laid significantly fewer eggs in surface treated with alkaline water. However, alkaline water treatment did not significantly affect the oviposition site choice of crickets and distribution pattern of earthworms. Result of field manipulations showed that long-term spraying of alkaline water could significantly reduce the abundance of soil microalgae and density of biting midges, but did not affect the diversity of non-target ground arthropods. These results demonstrate that long-term spraying of alkaline water could decrease biting midge density without harming co-existing non-target organisms and therefore is a potentially eco-friendly approach to control such pest.

Evaluation of winter cover crop methods for management of flatheaded appletree borer (Coleoptera: Buprestidae).

Winter cover crops grown at the base of red maples (Acer rubrum L.) can reduce flatheaded appletree borer (Chrysobothris femorata Olivier; Coleoptera: Buprestidae; FAB) damage by both physically blocking preferred oviposition sites and altering the environment around them. However, cover crop competition negatively affects tree growth. To investigate long-term cover crop effects, trees grown with cover crop for 2 yr were transitioned to a standard herbicide practice. After 4 yr, trees in the initial 2 yr cover crop plots were 1 yr behind in growth compared to trees grown in bare rows for all 4 yr. Most growth reduction occurred in the first year following transplant. Additional borer losses of 1-2% per year were observed in production years 3 and 4. A second experiment answered 2 questions: Can killing the cover crop once it reaches maximal height protect trees from borers while also reducing competition and thereby increase tree growth? and Do herbicide applications increase borer attacks? In this experiment, red maples were grown with (i) a standard herbicide program, (ii) a mulch mat, (iii) a cover crop that was killed early, or (iv) a cover crop allowed to senesce naturally. Evaluations after 2 yr indicated early kill of the cover crop was not enough to improve tree growth. Further, trees in the early kill cover crop treatment had the most FAB attacks. Cover crops allowed to senesce naturally reduced FAB attacks in both studies; however, more work is needed to minimize disparities in tree growth during the initial year post-transplant and determine the causal relationship between herbicide use and borer attacks.

Larval and adult experience and ecotype affect oviposition behavior in a niche-expanding butterfly

AbstractLocal adaptation, early-developmental and behavioral plasticity have all been suggested to be underlying mechanisms of behavioral variation. They allow organisms to cope with resource heterogeneity in time and space. However, the relative contribution of each of these drivers on niche-expansion success is still unclear. We addressed this issue by studying oviposition behavior in a butterfly (Pararge aegeria) that used to be confined to forest, but recently colonized anthropogenic areas too. We caught females of either forest or agricultural ecotype and allowed their larval offspring to experience early-habitat cues in either open field or woodland conditions. For 110 females of this transplant experiment, we monitored all oviposition-related behaviors (i.e., site selection, searching, motivation, learning) using repeated trials in outdoor flight cages with naturally occurring host grasses. We observed changes in oviposition site preference, with increasing preference for semi-shaded host grass (by vegetation or vertical structures) over consecutive egg-lays. Motivation to oviposit was most affected by larval experience (in interaction with cage environment). We also show evidence for ecotypic differentiation with the agricultural ecotype showing reduced search effort during the first trial compared to the forest ecotype. We argue that females of agricultural landscapes with fragmented resource distributions adopt a more risk-aversive oviposition strategy. Our detailed behavioral tracking under ecologically relevant conditions, stresses the importance of considering different types of behavioral plasticity to unravel a species’ success during niche expansion.

The toad less travelled: comparing life histories, ecological niches, and potential habitat of Asian black-spined toads and cane toads

Context Invasive vertebrates have significant negative impacts on biodiversity and agricultural production worldwide. Increased connectivity among countries, through trade and tourism, is escalating the rate of introductions of vertebrate species, particularly herpetofauna, across international borders. In Australia, Asian black-spined toads (ABSTs; Duttaphrynus melanostictus) are one of the species most intercepted at borders. They are considered a biosecurity risk because of the potential for negative environmental impacts, similar to those caused by cane toads (Rhinella marina). Aims We aimed to compare ABSTs with cane toads to investigate potential impacts and distribution of ABSTs in the Australian context. We also aimed to identify knowledge gaps regarding ABST biology and the potential role of cane toads in an ABST invasion in Australia. Methods We undertook a literature review to obtain published data to compare the life history characteristics of ABSTs and cane toads. We also modelled climatic niche overlap and compared suitable habitat for both species in Australia. Key results Our results show ABSTs and cane toads have broadly similar reproductive life histories and feeding niches. In particular, similarities include large clutch sizes, preferred oviposition sites, and diet at tadpole and adult life stages. In Australia, the species share suitable potential habitat, particularly in North Queensland, where the majority of ABST incursions have occurred. The species differ in size, call characteristics, clutch size relative to body size, and egg development rate, although the environment also influences these traits. We identify gaps in our knowledge of ABST spatial ecology, thermal tolerances, water reliance, and habitat. Conclusions ABSTs pose a significant biosecurity threat to Australia. Similarities in life history to cane toads means they may have similar impacts, but may have a more limited distribution in Australia. Invasion of Australia by ABSTs would likely result in interactions with cane toads, but it is not possible to accurately determine the outcomes of those interactions without further investigation. Implications Addressing knowledge gaps and quantitatively determining the potential for competition between ABSTs and cane toads will assist surveillance and response planning for ABST incursions in Australia.

Water hyacinth (Eichhornia crassipes) as an oviposition site for the disease transmitting snail Indoplanorbis exustus (Deshayes 1833) (Gastropoda: Planorbidae): implications in snail management

The water hyacinth (Eichhornia crassipes) is an invasive species in freshwater ecosystems with potential to alter habitat features and macroinvertebrate community composition. Many freshwater snails are associated with the water hyacinth for food and refuge. In the present study, an assessment of the water hyacinth as an oviposition site of the freshwater snail Indoplanorbis exustus was conducted through evaluation of the field collected plants. Apparently, the bulbous part of the water hyacinth was preferred over the leaves and the stems in terms of the egg capsules and eggs per egg capsule oviposited by I. exustus. A logistic regression indicated significant differences in the preferred oviposition sites by the snail. Owing to the invasion of the water hyacinth, the oviposition and further colonization by the snail I. exustus may be facilitated

Influence of Phaseolus vulgaris L. (Fabaceae: Fabales) varieties on oviposition behavior and susceptibility to infestation by Acanthoscelides obtectus Say (Coleoptera: Bruchidae)

Despite beans being a vital source of cheap protein, its yield is reduced mainly by diseases, field and storage pests. An effective and sustainable control option against storage insect pests could be improving the genetic resistance of the host plant in relation to the behaviour of the pest. A laboratory investigation was conducted to determine effects of bean varieties on oviposition behaviour and susceptibility to infestation by Acanthoscelides obtectus. The experiments evaluated oviposition site preference, number of eggs laid, and number of progeny and emergence holes of A. obtectus per bean variety. The number of progeny and duration in days taken by 50 % of progeny to emerge was determined and used to calculate susceptibility index. Seed harness index, thickness of testae and surface area of bean varieties were determined and related with susceptibility indices. Results indicated that the number of eggs laid, progeny, and emergence holes, duration taken by progeny to emerge, susceptibility indices, seed surface area and hardness were statistically different. Mwezi moja variety was the most preferred host for oviposition whereas Mwitemania was the least preferred. Beetles laid the highest (84.5) number of eggs in Mwezi moja and the least (41.9) in Mwitemania. Number of progeny of A. obtectus emerging were the highest in Mwezi moja (73.7) and the least (36) in Mwitemania. Beetles took the shortest (36.75 days) period to emerge from Mwezi moja and the longest (38.63days) period from Mwitemania. Mwezi moja was the most susceptible variety to attack by A. obtectus with a susceptibility index of 7.43 and Mwitemania was the least susceptible with an index of 6.51. Nyayo had the highest (0.019) seed hardness index and Mwezi moja and Canadian wonder had the least (0.012) hardness index. Mwezi moja had the largest (278mm) surface area whereas Mwitemania had the lowest (171mm) surface area.

Amblyseius herbicolus mothers prefer to oviposit near eggs of non-kin in the absence of prey Carpoglyphus lactis (Acari: Phytoseiidae, Carpoglyphidae)

Many animal species can recognise and discriminate conspecifics differing in their genetic relatedness. The discrimination of kin from non-kin or more distantly related kin can benefit individuals with increased inclusive fitness and avoid adverse influences from inbreeding. A preference by mothers to oviposit near their own or closely related eggs rather than ovipositing near non-kin or distantly related eggs has been observed in several phytoseiids, possibly to reduce cannibalism and allow imprinting between siblings. The phytoseiid Amblyseius herbicolus reluctantly cannibalise kin (i.e. siblings or offspring) in the presence of non-kin or more distantly related kin. This study investigated the oviposition preference of A. herbicolus females when provided with two sites, each containing either their own eggs or eggs laid by non-kin. The influence of food on such oviposition site preference is largely unknown in phytoseiids. Thus, we also examined the oviposition site choice of A. herbicolus females in the presence and absence of its prey Carpoglyphus lactis eggs. Our results demonstrated a significant influence of prey on the oviposition site preference of A. herbicolus: adults preferred to oviposit near eggs of non-kin in the absence of prey but showed no preference when C. lactis eggs were present at both sites. We suggest that A. herbicolus females preferred to oviposit near eggs of non-kin in the absence of prey to possibly avoid kin cannibalism during food stress.

Studies on gall-inducing behaviour and life cycle to aid host specificity testing of Notomma mutilum (Diptera: Tephritidae) – a prospective biological control agent for prickly acacia (Vachellia nilotica subsp. indica)

ABSTRACT The gall-inducing tephritid fly Notomma mutilum (Bezzi) (Diptera: Tephritidae) from Senegal is a prospective biological control agent of prickly acacia, Vachellia nilotica subsp. indica (Benth.) Kyal. & Boatwr (Fabaceae) in Australia. Wide variation in the oviposition behaviour and life cycle of N. mutilum in quarantine resulted in difficulties with colony maintenance and host specificity testing. To identify the factors responsible, adults that emerged from galls cut from plants 100 days after oviposition (enforced population, EP) were compared with adults that emerged from galls on the plants (normal population, NP). Oviposition by females of different ages did not vary significantly. The EP females had more variable egg-laying (galls on 46.8% plants) and made fewer oviposition scars (≈37 per female) than NP females (galls on >90% plants and ≈95 scars per female). However, the life cycle duration of EP progeny was shorter (140.7 ± 1.7 days) and less variable than NP progeny (160.1 ± 12.8 days). Egg-laying on all the plants was achieved when a greater number of EP adults (three pairs) were used. Actively growing tender shoots in the upper crown of the older host plants were preferred sites for oviposition. Galls were initiated (3.5 ± 0.2 days) before egg hatching (11.3 ± 0.3 days), and bigger (longer and wider) galls were observed on the preferred oviposition sites. Therefore, plants with actively growing shoots in the upper crown should be selected for host specificity testing and three pairs of N. mutilum adults should be used.

Population dynamics of Aedes aegypti (Diptera: Culicidae): Contributions to the prevention of arbovirosis in Villa Clara, Cuba

Emerging and re-emerging infectious diseases constitute one of the main health problems worldwide. The objective of the research consisted of analyzing the development dynamics of adult mosquito populations of the species Ae. aegypti in Villa Clara province, Cuba during the period 2016-2020. The research covered the 13 municipalities of Villa Clara. An observational, descriptive, ecological, retrospective and analytical-statistical (by decision tree/exploratory data analysis) study was conducted. The study was based on the collection of positive samples/number of outbreaks reported in the 13 municipalities of the province, in the different months of the period analyzed, for the mosquito species Ae. aegypti, where each sample point corresponded to the number of specimens collected in one of the years covered, with one of the months of the year in question (12 months), the 13 municipalities, and 9 types of reservoirs. This resulted in 7 020 observations, which constitutes the sample size. The presence of the species under analysis was found in the 13 municipalities of the province, with abundant population densities; on the other hand, the variables with the greatest incidence in the population dynamics were: municipality and type of reservoir, with emphasis on the low tank, as the preferred oviposition and breeding site for this species. It is concluded that Ae. aegypti has a high capacity for adaptation and high ecological plasticity, with a marked correspondence between the ecology and habitat of the species under analysis.

Culex quinquefasciatus larvae development arrested when fed on Neochloris aquatica.

Culex quinquefasciatus is a cosmopolitan species widely distributed in the tropical and subtropical areas of the world. Due to its long history of close association with humans, the transmission of arboviruses and parasites have an important role in veterinary and public health. Adult females feed mainly on birds although they can also feed on humans and other mammals. On the other hand, larvae are able to feed on a great diversity of microorganisms, including microalgae, present in natural or artificial breeding sites with a high organic load. These two particularities, mentioned above, are some of the reasons why this mosquito is so successful in the environment. In this work, we report the identification of a microalga found during field sampling in artificial breeding sites, in a group of discarded tires with accumulated rainwater. Surprisingly, only one of them had a bright green culture without mosquito larvae while the other surrounding tires contained a large number of mosquito larvae. We isolated and identified this microorganism as Neochloris aquatica, and it was evaluated as a potential biological control agent against Cx. quinquefasciatus. The oviposition site preference in the presence of the alga by gravid females, and the effects on larval development were analyzed. Additionally, microalga effect on Cx. quinquefasciatus wild type, naturally infected with the endosymbiotic bacterium Wolbachia (w+) and Wolbachia free (w−) laboratory lines was explored. According to our results, even though it is chosen by gravid females to lay their eggs, the microalga had a negative effect on the development of larvae from both populations. Additionally, when the larvae were fed with a culture of alga supplemented with balanced fish food used as control diet, they were not able to reverse its effect, and were unable to complete development until adulthood. Here, N. aquatica is described as a biological agent, and as a potential source of bioactive compounds for the control of mosquito populations important in veterinary and human health.

Natural variation at the Drosophila melanogaster Or22 odorant receptor locus is associated with changes in olfactory behaviour.

In insects, many critical olfactory behaviours are mediated by the large odorant receptor (Or) gene family, which determines the response properties of different classes of olfactory receptor neurons (ORNs). While ORN responses are generally conserved within and between Drosophila species, variant alleles of the D. melanogaster Or22 locus have previously been shown to alter the response profile of an ORN class called ab3A. These alleles show potential clinal variation, suggesting that selection is acting at this locus. Here, we investigated if the changes seen in ab3A responses lead to changes in olfactory-related behaviours. We show that variation at the Or22 locus and in the ab3A neurons are not fully compensated for by other ORNs and lead to overall changes in antennal odorant detection. We further show that this correlates with differences in odorant preference behaviour and with differences in oviposition site preference, with flies that have the chimaeric short allele strongly preferring to oviposit on banana. These findings indicate that variation at the Or22 locus leads to changes in olfactory-driven behaviours, and add support to the idea that the ab3A neurons are of especial importance to the ecology of Drosophila flies.

The predatory bug Orius strigicollis shows a preference for egg-laying sites based on plant topography.

BackgroundOviposition site selection is an important factor in determining the success of insect populations. Orius spp. are widely used in the biological control of a wide range of soft-bodied insect pests such as thrips, aphids, and mites. Orius strigicollis (Heteroptera: Anthocoridae) is the dominant Orius species in southern China; however, what factor drives its selection of an oviposition site after mating currently remains unknown.MethodsHere, kidney bean pods (KBPs) were chosen as the oviposition substrate, and choice and nonchoice experiments were conducted to determine the preferences concerning oviposition sites on the KBPs of O. strigicollis. The mechanism of oviposition behavior was revealed through observation and measurement of oviposition action, the egg hatching rate, and the oviposition time.ResultsWe found that O. strigicollis preferred the seams of the pods for oviposition, especially the seams at the tips of the KBPs. Choice and nonchoice experiments showed that females did not lay eggs when the KBP tail parts were unavailable. The rates of egg hatching on different KBP parts were not significantly different, but the time required for females to lay eggs on the tip seam was significantly lower. Decreased oviposition time is achieved on the tip seam because the insect can exploit support points found there and gain leverage for insertion of the ovipositor.DiscussionThe preferences for oviposition sites of O. strigicollis are significantly influenced by the topography of the KBP surface. Revealing such behavior and mechanisms will provide an important scientific basis for the mass rearing of predatory bugs.

Three chemosensory proteins from the sweet potato weevil, Cylas formicarius, are involved in the perception of host plant volatiles.

Chemosensory proteins (CSPs) play important roles in chemical communication, but their precise physiological functions are still unclear. Cylas formicarius is the most serious pest attacking sweet potato around the world. At present, there is no effective way to control this pest. Our results showed that CforCSP1, 5 and 6 genes were highly expressed in the antennae of both sexes of C. formicarius. In addition, results from a fluorescence competitive binding assay showed that the CforCSP1, 5 and 6 proteins had high binding affinities for 17 plant volatiles including eight host plant volatiles. This indicated that the three proteins may be involved in the detection of host plant volatiles. Furthermore, results from four-arm olfactometer bioassays showed that there was a significant tendency for C. formicarius to be attracted to eucalyptol, β-carotene, benzaldehyde, vanillin and phenethyl alcohol, while it was repelled by β-ionone. Finally, the levels of expression of the three CforCSPs in C. formicarius were successfully inhibited by RNA interference (RNAi). Behavioral experiments showed that CforCSP1, 5 and 6-deficient C. formicarius were partly anosmic to β-cyclocitral, benzaldehyde, octyl aldehyde, and β-ionone and exhibited a reduced ability to locate the host plant volatiles β-carotene and vanillin. Our data suggest that CforCSP1, 5 and 6 likely are involved in the chemical communication between C. formicarius and host plant volatiles, which may play pivotal roles in oviposition and feeding site preferences. More importantly, these results could provide information for the development of monitoring and push-pull strategies for the control of C. formicarius. © 2021 Society of Chemical Industry.

Oviposition by a lycaenid butterfly onto old host parts is adaptive to avoid interference by conspecific larvae.

Oviposition site selection by herbivores can depend not only on the quality of host resources, but also on the risk of predation, parasitism and interference. Females of the lycaenid butterfly Arhopala bazalus (Lepidoptera) lay eggs primarily on old host foliage away from fresh growth, where larval offspring live and feed. Resource availability of young host leaves seems not to affect the oviposition site preference by the females. To clarify the adaptive significance of A. bazalus oviposition behavior on old foliage, we tested three hypotheses: eggs on fresh foliage are (1) easily dropped during rapid leaf expansion (bottom-up hypothesis), (2) more likely to be attacked by egg parasitoids (top-down hypothesis), and (3) frequently displaced or injured by other herbivores (interference hypothesis). In field surveys, rates of egg dropping and parasitism by egg parasitoids were not significantly different between fresh and old host parts. However, the portions of fresh leaves on which A. bazalus eggs had been laid were cut from shoots on which conspecific larvae fed. Laboratory experiments demonstrated that eggs on young leaves were displaced in the presence of conspecific larvae and we observed that fifth instar larvae actively displaced conspecific eggs by feeding on the surrounding leaf tissue. These findings indicate that eggs laid on fresh leaves are at risk of being displaced by conspecific larvae, and support the interference hypothesis. Larval behavior is a likely evolutionary force for A. bazalus to lay eggs apart from larval feeding sites on the host plant.