Aim‐then‐shoot anemotaxis involved in the hopping approach of potato tuberworm moth Phthorimaea operculella toward a sex pheromone source

Male moths locate conspecific females by pheromone‐induced upwind flight maintained by detecting a visual flow, termed optomotor anemotaxis. Their behavioural pattern is characterized by an upwind surge in response to a pheromone stimulus and crosswind casting after odour loss, which is considered to be reset and restarted on receipt of another pheromone pulse. However, pheromone‐stimulated males of the potato tuberworm moth Phthorimaea operculella exhibit a series of short and straight intermittent flights, or hops, when moving upwind. It is unclear whether they navigate by employing the same behavioural pattern and wind detection mechanism as that used by flying moths. To analyze odour‐modulated anemotaxis in male potato tuberworm moths, a flat wind tunnel is constructed to give regular odour stimuli to an insect regardless of its location. Moths are subjected to pheromone pulses of different frequencies to test whether they show a behavioural pattern that is reset and restarted by a pheromone pulse. Moths on the ground are also subjected to crosswind shear to examine their detection of wind direction. Path analyses reveal that males surge upwind when they receive a pheromone pulse and exhibit casting by successive hops when they lose odour. This behavioural pattern appears to be similar to that of flying moths. When the direction of the airflow is switched orthogonally, males adjust their course angle accordingly when they are on the ground. It is suggested that, instead of optomotor anemotaxis, this ‘aim‐then‐shoot’ system aids the detection of wind direction, possibly by mechanosensory means.     

Effects of moth size on velocity and steering during upwind flight toward a sex pheromone source byLymantria dispar (Lepidoptera: Lymantriidae)

Free-flying male gypsy moths (Lymantria dispar)head upwind in response to sex pheromone. Males typically fly in a zigzag path, with mean ground speeds modulated by pheromone concentration and ambient temperature, but not by wind speed. We studied the effect of male size on ground speeds and additional flight track parameters. Mean net ground speed along the wind line was fastest among large males and was slower in medium and small males. Similarly, mean airspeeds and ground speeds along the flight tracks increased from small to large males. Males from all three size classes steered similar mean course angles. Small males, however, had larger mean track angles than larger males, and mean drift angles were also larger for small males. Turning rates (frequency of turns across the wind line) and interturn distances (net crosswind displacement between turn apices) were not significantly different among the three size classes; however, large males had a trend toward a reduced mean turning rate and increased mean interturn distance. The steering of similar course angles by males from all three size classes and the higher airspeeds among larger males (the two variables males can actively control during free flight) suggest that changes in other flight parameters are a result primarily of increased ground speed among large males.     

Effect of the fine-scale structure of pheromone plumes: pulse frequency modulates activation and upwind flight of almond moth males

Abstract. The effects of plume intermittency and volume on behavioural and flight responses to pheromone of male Cadra cautella (Walker) (Lepidoptera: Phycitinae) were investigated in a pulling wind tunnel. The fine-scale structure of turbulent pheromone plumes was mimicked and manipulated using a pulser device that generated continuous ribbon plumes or intermittent plumes with defined pulse frequency and volume. As pulse frequency increased from 0.6 to 5 Hz and injected volume increased from 0.5 to 5 mls^-1, males flew progressively higher air and ground speeds, turned less frequently, and steered smaller course angles, resulting in straighter flight tracks. The faster the frequency of pulses and the greater the volume of the plume, the higher the proportion of males responding, the shorter their latencies, and the less time spent in the behaviour. Flight tracks of male C.cautella to point sources of pheromone depend on the frequency of filaments encountered.     

蛾类昆虫雄性信息素及其功能

昆虫性信息素是两性通讯系统的基础,其中雄性信息素的研究相对较少。本文综述了蛾类昆虫雄性信息素的研究进展。迄今已鉴定出40余种蛾类昆虫的雄性信息素,其行为学功能主要有对雌性的引诱和激欲、对同种雄性的抑制及种间隔离等。     

Anemotactic orientation of gypsy moth males and its modification by the attractant pheromone (+)-disparlure during walking

ABSTRACT. Tracks of dewinged gypsy moth males, Lymantria dispar L. (Lymantriidae), walking upwind in an airstream without pheromone consist of marked alternations between more or less straight upwind segments, partly with an arcadic structure, and twisted segments. This apparently complicated behaviour can, however, simply be explained by a superposition of noise and two turning commands: an upwind turning tendency, derived from the anemoreceptive system, which represents an average of the moth's angular positions over a period of time; and an internal turning tendency which consists of strong but brief bursts. These bursts are produced intermittently; successive bursts do not necessarily alternate polarity. Amputation of one antenna increases the probability of bursts towards the amputated side; therefore a separate burst source is postulated for each antenna. In the presence of the attractant pheromone (+)-disparlure, the anemotactic signal is weighted higher; twisted segments are, therefore, less pronounced.
There is a chemotropotactical component involved in the male's orientation. The tropotactical signal, dependent on the difference of odour concentration perceived by the left and right antenna, competes with the upwind turning tendency.     

Influence of pheromone concentration and ambient temperature on flight of the gypsy moth, Lymantria dispar (L), in a sustained-flight wind tunnel

Abstract. The effects of pheromone concentration and ambient temperature on male gypsy moth, Lymantria dispar (L.) (Lepidoptera), flight responses to pheromone were investigated in a wind tunnel. As the pheromone dose increased from 10 ng to 1000 ng, males flew at progressively slower airspeeds and ground speeds, and reduced their wingbeat frequencies. Furthermore, the moths steered significantly smaller course angles as the pheromone concentration increased, indicating that they were adopting a more upwind heading. The overall width of the flight tracks also decreased when males flew in more concentrated pheromone plumes. Estimation of plume dimensions using a male wing-fanning assay showed that as pheromone dosage increased, the resultant active spaces became wider, indicating that an inverse relationship existed between the dimensions of the time-averaged plume and the width of track reversals and that most turns were initiated within the plume. When males were flown at cool (20°C) and warm (26°C) ambient temperatures but to equivalent pheromone emission rates, they exhibited higher airspeeds and ground speeds at the higher temperature but steered larger course angles. Track widths, and length of track legs were, however, similar at the two temperatures. The mean turning frequency was nearly the same (c. 4 turns/s) across all the concentrations and temperatures tested even though the moths' thoracic temperature differed by 5°C when the ambient temperature was varied.     

Attraction range of a sex pheromone trap for the damson‐hop aphid Phorodon humuli (Hemiptera: Aphididae)

The attraction range of olfactory response by winged female gynoparae (autumn migrants that give birth to oviparae, the sexual females) and male damson–hop aphids Phorodon humuli (Schrank) is investigated in field experiments over 2 years by analyzing the spatial patterns of catches in concentric circles of yellow‐painted traps (60 in total) around a central trap releasing the species' sex pheromone, (1RS,7S,7aS)‐nepetalactol. Males are more likely than females to be found in the central trap, with 65.6% of the 1824 males caught there compared with 11.2% of 1346 females. Both morphs are more numerous in traps axial with the mean wind direction and centred on the pheromone‐release trap than at other angles. Males are approximately five‐fold more numerous in traps downwind than at similar distances upwind of the pheromone, showing that its presence stimulates landing. For males, the estimated active space of the lure extends 6 m downwind. Catches of females are equally numerous up and downwind of the pheromone lure because females orienting on the axis of the pheromone source continue to respond to visual cues in their flight path if they overshoot the olfactory one. For females, the active space of a pheromone lure is less than 2 m downwind. It is unimportant for either morph whether the pheromone‐release trap is yellow or transparent. In these experiments, both morphs orient with, track and probably arrive in the pheromone source trap from at least 26 m, the distance to the nearest aphid‐infested hops.     

Visual cues collimate the trajectories of almond moth Cadra cautella males flying in wind and still air within a wind‐formed plume of pheromone

Male Cadra cautella (Walker) moths are videotaped in three dimensions in a 3‐m long wind tunnel as they fly within a 65‐cm wide plume of pheromone. Moths are presented two floor patterns, either ‘aligned’, a 25‐cm wide ‘trail’ of solid red circles along the tunnel's midline, or ‘offset’, in which the trail veers 25 cm to the left at the tunnel's midpoint. These visual patterns are presented either in a continuous airflow or airflow that is stopped before moths reach the tunnel's halfway point. Moths fly relatively straight paths over the aligned pattern in still air after the wind is stopped. With the offset pattern in wind and when the wind is stopped, moths swerve towards the offset pattern before again progressing along the plume. Prominent visual cues appear to ‘collimate’ (i.e. align with a directional cue) the moth's course as long as the moth remains in contact with pheromone. In wind, these moths appear to favour trajectories that enhance visual feedback, even if the path taken is not directly upwind. During wind lulls, this manoeuvre may enable moths to continue progress towards calling females along a visually set course. The centring of trajectory over prominent visual cues suggests that these moths favour a route that enhances visual feedback.     

How Trichogramma parasitoids use moth sex pheromones as kairomones: orientation behaviour in a wind tunnel

Abstract The orientation behaviour of Trichogramma egg parasitoids (T.evanescens Westwood and T.pretiosum Riley) in response to the sex pheromone of their noctuid hosts {Mamestra brassicae L. and Heliothis tea (Boddie)) was investigated in a wind tunnel. Wasps were released on platforms which served as models of leaves, and were exposed to overhead light and an air stream that was either clean or loaded with host sex pheromone. The wasps exhibited: upwind anemotaxis, which was not affected by odour; odour-modulated positive phototaxis; and odour-induced inverse orthokinesis. Compared with clean air, residence times, walking times and path lengths on a platform were higher in pheromone-loaded air than in clean air. In pheromone-loaded air, walking velocity was reduced. During locomotion on a horizontal platform, net movement was upwind, regardless of the presence or absence of pheromone in the air. On a platform inclined at 45^o, anemotaxis appeared offset by positive phototaxis. If wasps were released on top of a glass rod above a platform, host sex pheromone caused wasps to land shortly after take-off. These results are used to explain higher rates of parasitism of moth eggs in pheromone-treated plots in earlier field experiments.     

Identification of host‐plant chemical stimuli for the European grape berry moth Eupoecilia ambiguella

Olfaction is of major importance for survival and reproduction in moths. Males possess highly specific and sensitive olfactory receptor neurones to detect female sex pheromones. However, the capacity of male moths to respond to host‐plant volatiles is relatively neglected and the role that such responses could play in the sensory ecology of moths is still not fully understood. The present study aims to identify host‐plant stimuli for the European grape berry moth Eupoecilia ambiguella Hb. (Tortricidae, Lepidoptera), a major pest of vine in Europe. Headspace volatiles from Vitis vinifera L. cv. Pinot Noir, Vitis vinifera subsp. sylvestris and five other host‐plant species comprising five different families are analyzed by gas chromatography linked to electroantennogram (EAG) recording from male E. ambiguella antennae and by gas chromatography‐mass spectrometry. This procedure identifies 32 EAG‐active compounds, among them the aliphatic compounds 1‐hexanol, (Z)‐3‐hexenol, (Z)‐3‐hexenyl acetate and 1‐octen‐3‐ol; the terpenes limonene, β‐caryophyllene and (E)‐4,8‐dimethyl‐1,3,7‐nonatriene; and the aromatic compounds benzaldehyde and methyl salicylate. Male and female E. ambiguella show similar EAG response amplitudes to individual chemical stimuli and also to mixtures of plant volatiles, as represented by essential oils from ten other plant species. This possibly indicates a common role for plant compounds in the sensory ecology of the two sexes of E. ambiguella.     

Properties of the Δ11-desaturase enzyme used in cabbage looper moth sex pheromone biosynthesis

The biosynthesis of a large number of sex pheromone components of various moth species can be explained by invoking a Δ 11-desaturation of common fatty acids. A Δ11-desaturase system from Trichoplusia ni, the cabbage looper moth, is identified and partially purified. Some of its properties are defined and compared with those of the ubiquitous Δ-9 desaturase enzyme. Similarities between the two systems include subcellular location (microsomal), substrate specificity (16- and 18-carbon acids), and lack of sensitivity to carbon monoxide, while differences include cofactor preference (NADH rather than NADPH), sensitivity to cyanide ion, pH optimum (7.4-7.8 vs 6.8-7.2), and location in the organism (in the pheromone gland compared to generally distributed). The effects of insect age were also investigated.     

Reduction of the response to sex pheromone in the oriental fruit moth,Grapholita molesta (Lepidoptera: Tortricidae) following successive pheromonal exposures

The effects of prior pheromonal experience upon the pheromone- mediated upwind flight response was examined in the oriental fruit moth, Grapholita molesta(Busck) (Lepidoptera: Tortricidae). Adult male G. molestawere subjected to a parallel series of staggered and repeated pheromonal exposures in a sustained-flight wind tunnel. Levels of response to pheromone in male G. molestasignificantly decreased in a (a) rectilinear function with increased ages of individuals, (b) logarithmic function of successive trials, and (c) steeper logarithmic function of successive trials with increased dosage of sex pheromone. The baseline levels of responding were not affected by either the (a) dosage of sex pheromone, (b) posteclosion ages of individuals for their initial exposures once the main effect of age itself was estimated, (c) elapsed time in hours between trials, or (d) discrete days of testing as integral intervals, disregarding hours within days.     

Temporal distribution of PBAN‐like immunoreactivity in the hemolymph of Mamestra brassicae females in relation to sex pheromone production and calling behavior

A direct enzyme‐linked immunosorbent assay has been developed and applied to the analysis of PBAN immunoreactivity in female hemolymph of the cabbage armyworm, Mamestra brassicae. PBAN‐IR determinations have been carried out with third scotophase insects at different times of the photoperiod. The rhythm of calling and the pattern of pheromone production by third scotophase females at different times of the photoperiod have also been determined. PBAN‐IR and calling are well correlated. However, whereas pheromone titers decrease, both PBAN‐IR levels and percentage of calling females remain high in the last hours of the scotophase. These results are discussed in the context of the regulation of sex pheromone biosynthesis in M. brassicae. Arch. Insect Biochem. Physiol. 40:80–87, 1999. © 1999 Wiley‐Liss, Inc.     

CRISPR/Cas9‐mediated PBP1 and PBP3 mutagenesis induced significant reduction in electrophysiological response to sex pheromones in male Chilo suppressalis

Pheromone-binding proteins (PBPs) are thought to bind and transport sex pheromones onto the olfactory receptors on the dendrite membrane of olfactory neurons, and thus play a vital role in sex pheromone perception. However, the function of PBPs has rarely been demonstrated in vivo.In this study, two PBPs (PBP1 and PBP3) of Chilo suppressalis, one of the most notorious pyralid pests, were in vivo functionally characterized using insects with the PBP gene knocked out by the CRISPR/Cas9 system. First, through direct injection of PBP-single guide RNA (sgRNA)/Cas9 messenger RNA into newly laid eggs, a high rate of target-gene editing (checked with polled eggs) was induced at 24 h after injection, 21.3% for PBPl-sgRNA injected eggs and 19.5% for PBP3-sgRNA injected eggs. Second, by an in-crossing strategy, insects with mutant PBP1 or PBP3 (both with a premature stop codon) were screened and homozygous mutants were obtained in the G3 generation. Third, the mutant insects were measured for electroantennogram (EAG) response to female sex pheromones. As a result, both PBP mutant males displayed significant reduction in EAG response, and this reduction in PBP1 mutants was higher than that in PBP3 mutants, indicating a more important role of PBP1. Finally, the relative importance of two PBPs and the possible off target effect induced by sgRNA-injection are discussed. Taken together, our study provides a deeper insight into the function of and interaction between different PBP genes in sex pheromone perception of C. suppressalis, as well as a valuable reference in methodology for gene functional study in other genes and other moth species.     

Pheromone‐binding proteins in the Asian gypsy moth females,Lymantria dispar,recognizing the sex pheromone and plant volatiles

Lepidopterans are known to have different pheromone‐binding proteins with differential expression patterns that facilitate specific signal transduction of semiochemicals. Two PBPs of the Asian gypsy moth, Lymantria dispar, were reported to express in both females and males, but their physiological functions were unknown. Results showed that LdisPBP1 and LdisPBP2 were expressed in the sensilla trichodea of males and the s. trichodea and s. basiconica of females. When LdisPBP1 gene was targeted by RNA interference (RNAi) in males, the expression of LdisPBP1 and LdisPBP2 decreased by 69 and 76%, respectively, and when LdisPBP2 gene was targeted by RNAi, they decreased by 60 and 42%, respectively. In females, after treatment with LdisPBP1 dsRNA, LdisPBP1 and LdisPBP2 levels were reduced by 26 and 69%, respectively, and LdisPBP2 dsRNA reduced the relative expression of them by 4 and 62%, respectively. The expression of LdisPBP1 and LdisPBP2 was interdependent. Electroantennogram (EAG) recordings showed that LdisPBPs participate in the recognition of the sex pheromone in males, and the sex pheromone and plant volatiles in females. The function of LdisPBPs represents the sex‐specific roles.     

Determining the number of instars in potato tuber moth Phthorimaea operculella (Zeller) using density‐based DBSCAN clustering

The potato tuber moth (PTM), Phthorimaea operculella (Zeller), is an important pest of Solanaceae crops and especially devastating to potatoes. There is no significant difference in morphological characteristics of PTM from the first to third instar larvae; therefore, it is difficult to directly determine the number of instars of this pest based on morphology. In the present study, head capsule width and length and mandible width of 340 PTM individuals were measured. Density‐based spatial clustering of applications with noise (DBSCAN) clustering was used for instar grouping. The results of DBSCAN clustering were compared with those obtained using Gaussian mixture models and k‐means clustering; the results of the three clustering methods were verified using Brooks–Dyar rule, Crosby rule and linear regression model. The clusters obtained using the three methods were the same and comprised four PTM instars with three morphological characteristics. Moreover, the results of the three methods fit the Brooks–Dyar rule, Crosby rule, frequency analysis and logarithmic regression model well. Head capsule width was the best morphological characteristic for determining the number of instars of PTM, and this characteristic may be used for determining PTM instars in the field. These results show that the DBSCAN clustering method is a promising tool for the identification of insect instars.     

Area‐wide monitoring of potato tuberworm (Phthorimaea operculella) by pheromone trapping in Northern Italy: phenology,spatial distribution and relationships between catches and tuber damage

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