Circadian rhythms of insect pheromone titer, calling, emission, and response: a review

Temporal and Spatial Patterns of Mating in Rhodnius prolixus

The kissing bug Rhodnius prolixus is a nocturnal species; however, its temporal mating patterns remain unexplored. Copulation lasts about fifty minutes, during which time the couple remains almost motionless. We hypothesized that R. prolixus copulates within shelters to reduce its vulnerability. To test this, we examined the spatial and temporal patterns of its copulation, as well as the potential endogenous regulation of its circadian rhythm, under three conditions: a light:dark cycle (L/D), constant light (L/L), and constant darkness (D/D). Over ten days, the number and the timing of copulation of pairs in arenas containing a shelter were video-recorded. Under the L/D cycle, the pairs mated mainly during daylight hours. This rhythm persisted under the D/D cycle, with a peak extending from the first half of the subjective day to the first half of the subjective night. No rhythm was observed under the L/L cycle. A greater proportion of mating occurred within the shelters during the L/D and L/L cycles, whereas its spatial distribution was random under the D/D cycle. Our results reveal an endogenously controlled circadian rhythm of mating behavior, with mating activity mainly occurring during daylight hours. Additionally, we showed that the pairs copulated inside the shelters. These results provide new insights into the reproductive behavior of R. prolixus.

Physical and biological effects on moths' navigation performance

In a chemosensing system, the local olfactory environment experienced by a foraging organism is defined as an odorscape. Using the nocturnal pink bollworm moth (Pectinophora gossypiella), we tested the combined effect of three biophysical aspects in its immediate odorscape to shed light on the coupling effects of biotic and abiotic factors on navigation performances of a nocturnal forager: i) the quality of the pheromone source, ii) the pheromone availability, and iii) the airflow characteristics. The navigation performance of the males was investigated using a wind tunnel assay equipped with 3D infrared high-speed cameras. The navigation performance of the males was analyzed using ethological and biomechanical parameters.The results of this work indicate that: (1) the biophysical factors have combined effects on the navigation performance of mate-searching males; (2) Natural and sexual selection play an important role in shaping the pheromone-mediated sensory performance of nocturnal male moths; herein, the role of natural selection overrides that of sexual selection; (3) During odor-mediated mate-finding navigation, the male moth applies a tradeoff decision-making process based on weighted information from the biological and physical characteristics of the odorscape. This decision-making process includes weighting the tradeoff between the cost involved in flying under different flow conditions, the availability of different odor sources, and their quality.

Identification and Seasonal Abundance of Web- and Air-Borne Sex Pheromone Components of Western Black Widow Spiders, Latrodectus hesperus

Sex pheromones mediate mate location in many animal taxa. Widow spider males are attracted to sex pheromones disseminating from female webs. Upon arrival on a web, males court in response to web-borne contact pheromone components. N-3-Methylbutanoyl-O-methylpropanoyl-L-serine methyl ester (1) is the single known, weakly effective, contact pheromone component of female western black widows, Latrodectus hesperus. Moreover, the seasonal periodicity of pheromone signalling by female spiders is unknown. We tested the hypotheses that females of L. hesperus (1) deposit multiple contact pheromone components on their web that transition to mate-attractant pheromone components, and (2) increase pheromone signalling during the primary mating season. Analyses of web extract by gas and liquid chromatography-mass spectrometry (GC-MS; LC-MS) revealed N-3-methylbutanoyl-O-methylpropanoyl-L-serine (7), the corresponding acid of 1. Web extract of unmated female L. hesperus, and the synthetic blend of 1 and 7, were equally effective in eliciting courtship by males but web extract induced more sustained courtship. Tested singly, 7 prompted longer courtship behaviour by males than 1. Synthetic isobutyric acid (10), the hydrolysis product of 1 and 7, attracted male spiders in a field experiment. The abundance of 1 and 7 on female webs, with expected corresponding dissemination of 10 from webs, peaked during the summer when males are most abundant, indicating strategic sexual signalling by female spiders.

Clock genes regulate sex pheromone production and male mating ability in Bactrocera dorsalis

Many animals display physiological and behavioral activities limited to specific times of the day. Certain insects exhibit clear daily rhythms in their mating activities that are regulated by an internal biological clock. However, the specific genetic mechanisms underlying this regulation remain largely unexplored. Mating in the fruit fly Bactrocera dorsalis exhibits a daily rhythm and is dependent on sex pheromones produced in the male rectum. We used transcriptome sequencing and clustered regularly interspaced short palindromic repeats (CRISPR) / CRISPR-associated nuclease 9 techniques to understand whether the daily rhythmicity of mating in B. dorsalis and sex pheromone production in the rectum are regulated by clock genes. The results showed that the production of sex pheromones by B. dorsalis males is rhythmic (low during the day and high at night) and is influenced by clock genes. Knockout of the clock genes cryptochrome 1 (cry1) and timeless (tim) reduced the production of sex pheromones and significantly impaired mating ability in males. In addition, quantitative polymerase chain reaction results from 5 different tissues showed cry1 was highly expressed in the head, whereas tim was highly expressed in both the head and rectum (a key site for male sex pheromone production). Transcriptome analysis confirmed that cry1 (head) and tim (head and rectum) exhibit rhythmic expressions consistent with sex pheromone rhythmicity. These results suggest that cry1 may be related to a central clock neuron (like the suprachiasmatic nucleus), whereas the rhythmic expression of tim in the rectum indicates the potential presence of peripheral oscillators. Our study reveals new targets and ideas for improved control of the fruit fly.

Molecular module for glucose production influences sex pheromone synthesis in Bactrocera dorsalis

Some insects have evolved beneficial relationships with intestinal microbes for sex pheromone production to communicate with conspecifics effectively. However, it is not clear whether the sex pheromone synthesis activity of intestinal microbes can be controlled by the host, and the molecular mechanisms need to be further unraveled. In this study, we find that rectal gland Bacillus species of male Bactrocera dorsalis specifically produce sex pheromones in the evening, which is significantly associated with glucose levels. In vitro Bacillus culture assays show that glucose levels significantly influence the amount of sex pheromone produced. Comparative rectal gland transcriptome analysis reveals that the expressions of the alpha-galactosidase gene (GLA), a Bactrocera dorsalis transcription factor (BDTF), and a pigment-dispersing factor (PDF) are responsible for producing glucose. Our findings reveal that the PDF-BDTF-GLA module influences the intestinal-microbe-produced sex pheromone by regulating glucose levels and advance our understanding of interactions between insects and their intestinal microbes.

Rhythms in insect olfactory systems: underlying mechanisms and outstanding questions

Olfaction is a critical sensory modality for invertebrates, and it mediates a wide range of behaviors and physiological processes. Like most living organisms, insects live in rhythmic environments: the succession of nights and days is accompanied by cyclic variations in light intensity and temperature, as well as in the availability of resources and the activity of predators. Responding to olfactory cues in the proper temporal context is thus highly adaptive and allows for the efficient allocation of energy resources. Given the agricultural or epidemiological importance of some insect species, understanding olfactory rhythms is critical for the development of effective control strategies. Although the vinegar fly Drosophila melanogaster has been a classical model for the study of olfaction and circadian rhythms, recent studies focusing on non-model species have expanded our understanding of insect olfactory rhythms. Additionally, recent evidence revealing receptor co-expression by sensory neurons has brought about an ongoing paradigm shift in our understanding of insect olfaction, making it timely to review the state of our knowledge on olfactory rhythms and identify critical future directions for the field. In this Review, we discuss the multiple biological scales at which insect olfactory rhythms are being analyzed, and identify outstanding questions.

Circabidian rhythm of sex pheromone reception in a scarab beetle

Animals have endogenous clocks that regulate their behavior and physiology. These clocks rely on environmental cues (time givers) that appear approximately every 24 h due to the Earth's rotation; thus, most insects exhibit a circadian rhythm. One notable exception is the scarab beetle, Holotrichia parallela, a severe agricultural pest in China, Japan, South Korea, and India. Females emerge from the soil every other night, reach the canopy of host plants, evert an abdominal gland, and release a pheromone bouquet comprising l-isoleucine methyl ester (LIME) and l-linalool. To determine whether this circa'bi'dian rhythm affects the olfactory system, we aimed to identify H. parallela sex pheromone receptor(s) and study their expression patterns. We cloned 14 odorant receptors (ORs) and attempted de-orphanizing them in the Xenopus oocyte recording system. HparOR14 gave robust responses to LIME and smaller responses to l-linalool. Structural modeling, tissue expression profile, and RNAi treatment followed by physiological and behavioral studies support that HparOR14 is a sex pheromone receptor-the first of its kind discovered in Coleoptera. Examination of the HparOR14 transcript levels throughout the adult's life showed that on sexually active days, gene expression was significantly higher in the scotophase than in the photophase. Additionally, the HparOR14 expression profile showed a circabidian rhythm synchronized with the previously identified pattern of sex pheromone emission. 48 h of electroantennogram recordings showed that responses to LIME were abolished on non-calling nights. In contrast, responses to the green leaf volatile (Z)-3-henexyl acetate remained almost constant throughout the recording period.

Gymnandrosoma aurantianum (Lepidoptera: Tortricidae): Calling Rhythm and Effect of Age on Female Sex Pheromone Titer and Male Antennal Responses

The macadamia nut borer, Gymnandrosoma aurantianum Lima (Lepidoptera: Tortricidae), is the main pest of Macadamia integrifolia Maiden & Betche (Proteales: Proteaceae) in Central America. Despite its importance, there is little information on its reproductive behavior. We studied the calling behavior and effect of age on female sex pheromone production and male antennal response to the pheromone. Calling behavior of G. aurantianum females occurred at the onset of scotophase, between 17:00 and 20:00 h. The mean time spent calling was 64 min. It was observed that 30% of the 50 females exhibited a calling posture characterized by extrusion of the pheromone gland from the tip of the abdomen and they spread their wings slightly. Female age had no influence on the sex pheromone production, while male antennal response increased with age and pheromone dosage. The information obtained in this work contributes to understanding the sexual behavior of G. aurantianum and thus to the creation of strategies to control this important pest in macadamia.

Sexual Dimorphism, Diel Activity, and Mating Behavior of Eubulus cf. elongatus: an Emergent Pest Root in Cassava Crops

Eubulus cf. elongatus Hustache (Coleoptera: Curculionidae) is a Neotropical species recently considered an important pest of cassava (Manihot esculenta Crantz) in Brazil. This weevil feeds on cassava roots under the soil, which makes detection and control by traditional methods as pesticide quite ineffective. Besides that, no information is available about morphology, sex identification, and behavior. Given its recent category as a pest, its morphology, sex identification, and behavior were previously unknown. Laboratory reared adults of E. cf. elongatus emerged from pupal chambers originated from Embrapa Cerrados (Planaltina, Federal District, Brazil) were used to investigate sexual dimorphism, sex ratio, diel activity, and mating behavior. The visible sexual dimorphism was observed in the hind tibiae of females, which presents a more expansive distal portion than a proximal portion. The sex ratio analysis of E. cf. elongatus evidenced a proportion of males and females, approximately 1:1 in 2018, while 1.5:1, both similar to other species of curculionids. Males and females show predominantly nocturnal activity, including the mating attempts during scotophase. Three distinct phases of mating behavior developed by E. cf. elongatus are described: (i) pre-copulation, (ii) copulation, and (iii) post-copulation. The results obtained in this study provide essential information for developing monitoring and control strategies within an integrated management program for this critical pest species in cassava crops in Brazil.

Widow spiders alter web architecture and attractiveness in response to same-sex competition for prey and mates, and predation risk

Female-female competition in animals has rarely been studied. Responses of females that compete context-dependently for mates and prey, and seek safety from predators, are ideally studied with web-building spiders. Cobwebs possess unique sections for prey capture and safety, which can be quantified. We worked with Steaoda grossa females because their pheromone is known, and adjustments in response to mate competition could be measured. Females exposed to synthetic sex pheromone adjusted their webs, indicating a perception of intra-sexual competition via their sex pheromone. When females sequentially built their webs in settings of low and high intra-sexual competition, they adjusted their webs to increase prey capture and lower predation risk. In settings with strong mate competition, females deposited more contact pheromone components on their webs and accelerated their breakdown to mate-attractant pheromone components, essentially increasing their webs' attractiveness. We show that females respond to sexual, social and natural selection pressures originating from intra-sexual competition.

RNAi-mediated silencing of SlitPer disrupts sex pheromone communication behavior in Spodoptera litura

BACKGROUND

The 24-h circadian rhythm is considered crucial for insect sexual communication. However, its molecular mechanisms and signaling pathways, particularly the roles of the clock gene period (Per), remain largely unclear. The sex pheromone communication behavior of Spodoptera litura displays typical circadian rhythm characteristics. Thus, it represents an excellent model for functional analyses of the clock gene Per.

RESULTS

In this study, we investigated the potential roles of SlitPer in regulating sex pheromone communication in S. litura using RNA interference, quantitative real-time polymerase chain reactions (qPCR), gas chromatography, and behavioral assays. The qPCR results showed that the expression levels of SlitPer and two desaturase genes (SlitDes5 and SlitDes11) in the siPer group differed significantly at most time points from those in the siNC group. Dynamic variation in the three major sex pheromone titers and calling behavior of S. litura females in the siPer group was disordered. In addition, the mating rates of siPer S. litura females decreased significantly by 33.33%. Oviposition by mated siPer females was substantially reduced by 84.84%.

CONCLUSION

These findings provide a fundamental basis for elucidating the molecular mechanism by which Per regulates sex pheromone communication behavior in lepidopteran species. © 2023 Society of Chemical Industry.

The clock gene, period, influences migratory flight and reproduction of the oriental armyworm, Mythimna separata (Walker)

The oriental armyworm, Mythimna separata, is a major long-distance migratory insect pest of grain crops in China and other Asian countries. Migratory flights and reproductive behavior usually occur at night, regulated by a circadian rhythm. However, knowledge about the linkages between adult flight, reproduction, and clock genes is still incomplete. To fill this important gap in our knowledge, a clock gene (designated Msper) was identified and phylogenetic analysis indicated that the encoded protein (MsPER) was highly similar to PER proteins from other insect species. Quantitative RT-PCR assays demonstrated that significantly different spatiotemporal and circadian rhythmic accumulations of mRNA encoding MsPER occurred during development under steady 14 h : 10 h light : dark conditions. The highest mRNA accumulation occurred in adult antennae and the lowest in larvae. Msper was expressed rhythmically in adult antennae, relatively less in photophase and more entering scotophase. Injecting small interference RNA (siRNA) into adult heads effectively knocked down Msper mRNA levels within 72 h. Most siRNA-injected adults reduced their evening flight activity significantly and did not exhibit a normal evening peak of flight activity. They also failed to mate and lay eggs within 72 h. Adult mating behavior was restored to control levels by 72 h post injection. We infer that Msper is a prominent clock gene that acts in regulating adult migratory flight and mating behaviors of M. separata. Because of its influence on migration and mating, Msper may be a valuable gene to target for effective management of this migratory insect.

Comparative expression profiles of carboxylesterase orthologous CXE14 in two closely related tea geometrid species, Ectropis obliqua Prout and Ectropis grisescens Warren

Insect carboxylesterases (CXEs) can be expressed in multiple tissues and play crucial roles in detoxifying xenobiotic insecticides and degrading olfactory cues. Therefore, they have been considered as an important target for development of eco-friendly insect pest management strategies. Despite extensive investigation in most insect species, limited information on CXEs in sibling moth species is currently available. The Ectropis obliqua Prout and Ectropis grisescens Warren are two closely related tea geometrid species, which share the same host of tea plant but differ in geographical distribution, sex pheromone composition, and symbiotic bacteria abundance, providing an excellent mode species for studies of functional diversity of orthologous CXEs. In this study, we focused on EoblCXE14 due to its previously reported non-chemosensory organs-biased expression. First, the EoblCXE14 orthologous gene EgriCXE14 was cloned and sequence characteristics analysis showed that they share a conserved motif and phylogenetic relationship. Quantitative real-time polymerase chain reaction (qRT-PCR) was then used to compare the expression profiles between two Ectropis spp. The results showed that EoblCXE14 was predominately expressed in E. obliqua larvae, whereas EgriCXE14 was abundant in E. grisescens at multiple developmental stages. Interestingly, both orthologous CXEs were highly expressed in larval midgut, but the expression level of EoblCXE14 in E. obliqua midgut was significantly higher than that of EgriCXE14 in E. grisescens midgut. In addition, the potential effect of symbiotic bacteria Wolbachia on the CXE14 was examined. This study is the first to provide comparative expression profiles of orthologous CXE genes in two sibling geometrid moth species and the results will help further elucidate CXEs functions and identify a potential target for tea geometrid pest control.

Behavioural and Electrophysiological Response of Anastrepha fraterculus (Diptera: Tephritidae) to a γ-Lactone Synthetic Semiochemical

Attractants are a powerful tool for pest management. The lack of specific attractants for the South American fruit fly, Anastrepha fraterculus, a complex of cryptic species of great economic importance in South America, makes it difficult to monitor the pest in the field. The γ-lactone male sex and aggregation pheromones of several Anastrepha species, naturally released in a 7:3 epianastrephin to anastrephin ratio, and a structurally related naturally occurring γ-lactone ((±)-trans-tetrahydroactinidiolide) with gem-dimethyl groups (dimethyl) at C(4), were evaluated as potential attractants of this species. Different age and mating conditions of A. fraterculus males and females were evaluated during electroantennography (EAG) and field cage experiments in which polymeric lures were deployed to contain 100 mg of attractant. Epianastrephin and dimethyl were EAG+ for all fly conditions, with epianastrephin eliciting the highest response for both sexes and immature flies showing greater responsiveness than mature flies. In the field cage experiments, immature flies were only attracted to leks; virgin females were attracted to leks, dimethyl, and both epianastrephin-anastrephin formulations (95 and 70 wt.% epianastrephin); mature-mated males were attracted to leks, dimethyl and 70 wt.% epianastrephin; and mature-mated females were only attracted to leks. Our bioassays showed a promising performance of the analog dimethyl since it elicited the same response as epianastrephin, requires fewer steps to synthesize, and contains one less chiral center than the natural pheromones. The attraction to leks was recorded for all mating conditions and ages of flies and suggests that air-borne volatiles of calling males contain cues that could act as sensory traps. The addition of any of these compounds in the synthetic attractants may result in a greater attraction and thus deserves further evaluation. Dose-response experiments will provide additional information to move a step forward and validate the results obtained in open-field conditions.

The phototactic rhythm of pests for the Solar Insecticidal Lamp: A review

Pest management has been a great challenge since the beginning of human agricultural activities. Since the 1930s, chemical pesticide control has been a major control technology that can solve some of the pest problems in agricultural production. Still, it is harmful to food safety and the ecological environment. Meanwhile, the extensive use of chemical pesticides may lead to the rapid development of pest resistance. Because of the advantages of low cost, eco-friendly advantage, and low side effects, Solar Insecticidal Lamp (SIL) as the main physical control technology has been widely used for pest management in agricultural production in China. Owing to the phototaxis of pests, they have a phototropic rhythm during the nighttime. We can adjust the SIL insecticidal time according to the phototropic rhythm of pests. The purpose of this paper is to provide a comprehensive review of the pest phototactic rhythm in a selection of 24 pest species. It is the first comprehensive survey on the phototactic rhythm of pests and the time segments of this survey are accurate to the hour. The phototactic rhythm of pests are investigated in two different varieties of crops: 1) food crops and 2) economic crops. We also discuss and analyze the various factors (e.g., meteorological conditions, insecticidal devices, physiological states and others) that affect the changing phototactic rhythm of pests. Finally, we highlight some open research challenge issues and future directions.

Volatiles as Attractants of Mahogany Shoot Borer, Hypsipyla grandella Zeller (Lepidoptera: Pyralidae)

The mahogany shoot borer, Hypsipyla grandella Zeller (Lepidoptera: Pyralidae), is one of the most economically important pests in all American tropical forests because it prevents the establishment of monoculture plantations of the family Meliaceae, such as Spanish cedar, Cedrela odorata L. Various studies have focussed on the bioecological aspects and the chemical and silvicultural control of this pest. However, relatively little is known about the biological interactions between this insect and its host plant. In this study, the shoot borer's behavior and attraction response to cedar host plants was evaluated in field cages. We also identified the volatiles emitted by healthy C. odorata plants that were attractive to H. grandella adults. The attraction to headspace volatiles from cedar plants and a synthetic blend were evaluated in a Y-glass tube olfactometer. We observed that virgin and mated females exhibited low activity at night, frequent movement of the antennae, sporadic flight activity, and short (< 10 s) and long (> 30 s) wing-fanning. Virgin females assumed a calling position, whereas mated females exhibited three periods of oviposition. The results showed that all evaluated categories - virgin females, virgin males, and mated females - were attracted to cedar plants. We identified the following volatile compounds: α-pinene, (E)-β-ocimene, 2-ethyl-1-hexanol, limonene, nonanal, (E)-4,8-dimethyl-1,3,7-nonatriene, α-copaene, β-caryophyllene, and germacrene D. A synthetic blend significantly attracted virgin male and mated female shoot borers. Our results suggested that C. odorata volatiles compounds are responsible for the attraction of H. grandella.

An Efficient and Simple Method for Collecting Haemolymph of Cerambycidae (Insecta: Coleoptera) Adults

Cerambycid beetles (Cerambycidae) are major forest pests, posing a serious threat to the security of forest resources worldwide. Extensive research has focused on the control of cerambycid beetles from physiological and biochemical perspectives. Despite the important roles of insect haemolymph in physiological processes, efficient collection methods for Cerambycidae are lacking. For the efficient and easy collection of large amounts of pure haemolymph from adult cerambycid beetles, a new method, named net centrifugation, was developed. Three species of cerambycid beetles with large differences in size, Anoplophora chinensis, Monochamus saltuarius and Saperda populnea, were selected for the study. Haemolymph was collected by the newly developed net centrifugation method-in which an inner nylon net is used during centrifugation under optimised conditions, and a relatively small wound is generated on the insect-as well as the traditional tearing method and double centrifugation method. Among the three methods evaluated, the net centrifugation method caused the least damage to cerambycid beetles during the whole operation. This method resulted in the most haemolymph from a single beetle, with the lowest turbidity, mostly pure haemocytes in the precipitate, the clearest haemolymph smears by microscopy and the highest quality of RNA extracted from haemocytes. The net centrifugation method has a high collection efficiency, providing important technical support for haemolymph extraction and entomological research.

Seasonal and Diel Communication Periods of Sympatric Pest Limonius Click Beetle Species (Coleoptera: Elateridae) in Western Canada

In western North America, sympatric Limonius click beetle species produce limoniic acid [(E)-4-ethyloct-4-enoic acid] as a sex pheromone component (L. canus (LeConte), L. californicus (Mannerheim)) or respond to it as a sex attractant (L. infuscatus (Motschulsky)). We tested the hypothesis that these three congeners maintain species-specificity of sexual communication through nonoverlapping seasonal occurrence and/or contrasting diel periodicity of sexual communication. Using capture times of beetles in pheromone-baited traps as a proxy for sexual communication periods, our data show that L. canus and L. californicus have seasonally distinct communication periods. Most L. canus males (>90%) were captured in April and most L. californicus males (>95%) were captured in May/June/July. As almost exclusively L. infuscatus males were captured in two separate 24-hr trapping studies, with data recordings every hour, it remains inconclusive whether the three Limonius congeners communicate at different times of the day. Males of L. infuscatus responded to pheromone lures only during daytime hours and during the warmest period each day. Captures of L. infuscatus overlapping with those of L. canus in April and those of L. californicus in May/June imply the presence of reproductive isolating mechanisms other than seasonal separation of sexual communication periods.

Diel Periodicity in Males of the Navel Orangeworm (Lepidoptera: Pyralidae) as Revealed by Automated Camera Traps

Navel orangeworm, Amyelois transitella (Walker), is a key pest of walnuts, pistachio, and almonds in California. Pheromone mating disruption using timed aerosol dispensers is an increasingly common management technique. Dispenser efficiency may be increased by timing releases with the active mating period of navel orangeworm. Past work found that the peak time of sexual activity for navel orangeworm females is 2 h before sunrise when temperatures are above 18°C. Inference of male responsiveness from data collected in that study was limited by the necessity of using laboratory-reared females as a source of sex pheromone emission to attract males and the inherent limitations of human observers for nocturnal events. Here we used camera traps baited with artificial pheromone to observe male navel orangeworm mating response in the field over two field seasons. Male response to synthetic pheromone exhibited diel patterns broadly similar to females, i.e., they were active for a brief period of 2-3 h before dawn under summer conditions and began responding to pheromone earlier and over a longer period of time during spring and fall. But contrary to the previous findings with females, some males were captured at all hours of the day and night, and there was no evidence of short-term change of pheromone responsiveness in response to temperature. Environmental effects on the response of navel orangeworm males to an artificial pheromone source differ in important ways from the environmental effects on female release of sex pheromone.

Modelling push-pull management of pest insects using repellents and attractive traps in fruit tree orchards

BACKGROUND

Push-pull with semiochemicals in pest management uses repellents to reduce response of pests to food-mate resources (push) and attractive traps to reduce populations (pull). Simulation models of push-pull can aid understanding of plant-insect interactions in nature and suggest hypotheses for field tests that improve management. A previous model indicated advantages of push-pull for controlling ambrosia beetle, Euwallacea fornicatus, pest of avocado trees. However, the simulated behavior of repellency was inconsistent with field observations.

RESULTS

We simulated individual-based movement of insects in push-pull to reveal relationships between parameters of radii (strength) of attractive traps, pest aggregations, and repellents with densities of each in an avocado orchard to visualize and understand the interactions and significance. Simulations indicated placement of traps along a 1-ha area periphery as a barrier resulted in similar trapping and mating as when traps were in a grid, either when insects originated randomly inside the plot or came from outside the plot. However, when insects originated from outside, both arrangements caught slightly more than when insects originated within the plot.

CONCLUSION

There were no differences in capture rates whether traps were spaced in a barrier along the plot's periphery or in a grid covering the plot. Push-pull was more effective than pull (mass trapping) alone. Repellent behavior of individuals when encountering a repellent radius was modelled by approximate 90° turns (right or left at random) when about to enter an infestation, consistent with earlier observations of effects of repellents on bark beetles orienting to aggregation pheromone. © 2022 Society of Chemical Industry.