Direct and correlated responses to artificial selection on flight activity in the oriental fruit moth (Lepidoptera: Tortricidae)

The ability of a sufficient number of individuals to disperse is crucial for long‐term survival of populations. However, dispersal is often energetically costly, and thus is expected to trade‐off against other life‐history traits. In insect pest species, the occurrence of individuals with high flight activity challenges management practices. We performed artificial selection on flight activity and measured correlated responses to selection in the oriental fruit moth, Grapholita (= Cydia) molesta, a widely distributed and expanding lepidopteran pest of fruit crops. Both sexes rapidly responded to the imposed regime of divergent selection, indicating an adaptive potential of flight activity in this species. Upward‐selected moths died sooner than downward‐selected ones, providing evidence for a cost of flight activity to adult survival, reputedly associated with enhanced metabolic rates. Oppositely‐selected females had similar total reproductive output, disproving a trade‐off between dispersal and reproduction, although females with higher flight activity laid their eggs sooner. The ratio of body weight to forewing surface (forewing loading) did not significantly differ between selected lines. The present study contributes to the understanding of dispersal evolution, and also provides new insights into life‐history theory as well as important baseline data for the improvement of pest management practices. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 879–889.     

Sex pheromone dosage and blend specificity of response by oriental fruit moth males

The sex pheromone-mediated responses of male oriental fruit moths, Grapholitha molesta (Busck), to an array of blends and dosages of Z8-12Ac and E8-12:Ac, were analyzed. Males exhibited sustained upwind flight resulting in source location only to intermediate blends and dosages. This optimal range of treatments appeared to be bounded by dosages too low or too high to result in significant attraction (net within-plume displacement toward the source), the higher concentrations causing arrestment (no net within-plume displacement) at some distance from the source. Similar results were obtained in field-trapping studies with the same treatments, except that the optimal dosages were moved up about 10-fold. Increased turning and decreased linear velocity could account for arrestment with increasing amounts of the (E) isomer in high dosages and high (E)/(Z) ratio blends.

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Zusammenfassung Das Sexualverhalten männlicher Falter des Pfirsichtriebwicklers, Grapholitha molesta (Busck), gegenüber verschiedenen Dosierungen und Mischungen von (Z)-8- und (E)-8-Dodecenylacetat wurde untersucht. Ein stetiger Aufwindflug, der zum Auffinden der Duftquelle führte, konnte nur im mittleren Dosierungs- und Mischungsbereich beobachtet werden. Ausserhalb dieses Optimums war die Dosierung offenbar entweder zu hoch oder zu niedrig, um eine deutliche Anlockung, d.h. einen gerichteten Flug innerhalb der Duftfahne zu bewirken; bei hoher Konzentration näherten sich die Tiere der Quelle nur auf bestimmte Distanz (arrestment). Freilandversuche mit Fallen führten zu ähnlichen Ergebnissen, nur dass dort das Dosierungsoptimum bei ca. zehnmal höheren Werten lag als in den Versuchen im Windkanal. Der bei hohen Mengen an E-Isomer (hohe Dosis oder hohes E/Z-verhältnis) beobachtete Arrestment-Effekt könnte auf Erhöhung der Drehbewegungen oder Verringerung der Fluggeschwindigkeit zurückzuführen sein.

     

Effect of varying proportions of the alcohol component on sex pheromone blend discrimination in male Oriental fruit moths

ABSTRACT. The flight response of individual male Oriental fruit moths, Grapholitha molesta (Busck), was observed in a sustained-flight tunnel to 100 blend–dosage combinations of the three sex pheromone components: (Z)- and (E)-8-dodecenyl acetate and (Z)-8-dodecen-l-ol (1, 3, 10, 30 and 100 μg of Z8-12: AC with, 2, 6, 10, 20% E and, 0, 3, 10, 30 or100% OH alcohol added). Complete flights to the source were observed only to blend combinations containing all three components. Males exhibited highest response levels to two dosages (3 and 10μg) of the natural 6% E blend and these levels were relatively unaffected by changes in the proportion of Z8-12: OH. Certain treatments surrounding the peak area also elicited high response levels compared to the 6% E treatments, but these were strongly dependent on the proportion of OH in the blend. Hierarchical cluster analysis was utilized to compare and group treatments that elicited similar levels of response over the entire flight sequence and to derive an area of blend-dosage combinations within the matrix tested that elicited peak levels of attraction. Analysis of the response patterns for suboptimal treatments adjacent to the area of optimal attraction showed that response specificity was controlled by two major effects on flight behaviour, one occurring early in the flight sequence affecting male orientation to the odour plume, and the other occurring later in the sequence as an arrestment of upwind flight. These effects were strongly influenced by changes in the OH component and the E isomer, with the latter playing the critical role in effecting flight behaviour. Temporal analysis of the flight response to treatments within the optimal area showed that whereas the % OH did not significantly affect the magnitude of response, increasing the level of Z8-12: OH in the blend did significantly increase the duration of each phase of the behavioural sequence. Considering both the magnitude and temporal aspects of male response, optimal attraction in male OFM was best characterized by a small area of treatments around the peak 6% E blends that contained 10% OH. Finally, field tests showed a high degree of correlation between trends in response with changing proportion of Z8-12: OH as observed in the flight tunnel. Peak dosages were generally higher in the field, however, compared to those in the flight tunnel.     

Response of female oriental fruit moth to volatiles from apple and peach trees at three phenological stages

The attractiveness of peach ( Prunus persica L. Batsch) and apple ( Malus domestica L. Borkh.) (both Rosaceae) tissue to gravid female oriental fruit moth, Grapholita (=  Cydia ) molesta (Busck) (Lepidoptera: Tortricidae), was assessed at three distinct stages throughout the growing season using a dual-choice bioassay. Plant material offered to the female moths consisted of a plant shoot in early spring, before fruit became available. Later, it consisted of a leaf-bearing twig and a fruit, either alone or in combination. The level of attraction of the female moths to the various plant tissues varied substantially over time and according to the plant species. Before fruit became available, female moths were significantly attracted to peach as well as to apple shoots. During the early fruit growth stage, moths were attracted to a leaf-bearing twig originating from a peach tree, but not to that from an apple tree. In peach, it was the vegetative tissue that accounted for the attraction, whereas in apple, it was the reproductive tissue (a developing fruit). During the late fruit growth stage, both peach fruit and apple fruit were highly attractive, whereas a twig with leaves from either an apple or a peach tree was neither attractive nor repellent to the female moths. This changing female olfactory response to volatiles emitted by vegetative tissue and fruits from the two host plant species with progressing season is discussed with respect to the biology and the dispersal of this moth species.     

The effects of pheromone concentration on the flight behaviour of the oriental fruit moth, Grapholitha molesta

ABSTRACT. Male oriental fruit moths, Grapholitha molesta (Busck) (Tortricidae), flew at lower overall and net ground velocities when they flew toward higher concentration pheromone sources. Turning frequency was greater with increased pheromone concentration, while the distance of turns from the plume axis back towards the axis decreased. Turning magnitude and inter-reversal track angles remained constant at all concentrations tested. Concomitant with the changes in ground velocity but constant inter-reversal angles, were decreases in airspeed, decreases in the moths' course angles and increases in their drift angles. The significance of these changes is discussed in relation to their possible role in a longitudinal chemoklinotactic programme of turning operating in conjunction with anemotaxis to allow location of a pheromone source in wind.     

A non-anemotactic mechanism used in pheromone source location by flying moths

ABSTRACT. Male oriental fruit moths, Grapholitha molesta (Busck) (Tortricidae), continue to zigzag along a pheromone plume to the source in zero wind, if they have started flight with wind on. If the pheromone source is removed and the plume is hence truncated, moths flying in zero wind out of the end of the plume into clean air increase the width of their reversals and the angles of the straight legs of the tracks so they are more directly across the former wind line. Such moths reach the source less often than do those flying along a continuous plume. The males continue to zigzag up a plume in zero wind, apparently by a combination of sequential sampling of concentration along their path and the performance of an internal, self-steered programme of track reversals (zigzags) whose frequency increases with concentration. Visual feedback may aid in the still-air performance of the zigzags. We propose that both the sequential sampling (longitudinal klinotaxis) and self-steered counter-turning programme also are used in wind as well; anemotaxis apparently polarizes the direction of the zigzags to result in upwind displacement, and the narrow zigzags caused by the higher concentration in the plume keep the male 'locked on' to the odour.     

Optomotor anemotaxis polarizes self-steered zigzagging in flying moths

ABSTRACT. Experiments with oriental fruit moth males, Grapholita molesta (Buck), provide evidence that a pheromone plume in zero wind elicits an endogenous, self-steered programme of counterturning (zigzagging) flight, and that wind experienced in flight establishes the polarity of the counterturns; they become aligned so that displacement occurs toward the source, even after the wind is stopped. In zero wind, males located a pheromone source more frequently when they had experienced a wind after having already taken flight before the wind was stopped (46%) compared with those that took flight later and therefore only experienced wind while they were in contact with the ground (14%). Furthermore, males placed in a stationary pheromone plume in zero wind located the source, eventually, on 21% of occasions. The flight tracks of these males, as well as those having experienced a wind only while on the ground, often exhibited repetitive counterturns (zigzags) of c. 180–200. However, the counterturns meandered around the flight tunnel, the inter-reversal track angles having no consistent direction. Sometimes the males displaced down-tunnel in the stationary plume, sometimes up, eventually locating the source and performing a courtship display. The inter-reversal track angles of males counterturning in wind, on the other hand, displayed a consistent orientation of c. 60 to either side of the wind line, resulting in consistent upwind displacement toward the source. With no pheromone present, with or without wind, counterturns were not observed.     

Optomotor regulation of ground velocity in moths during flight to sex pheromone at different heights

ABSTRACT. Males of two species of moths ( Grapholitha molesta (Busck) and Heliothis virescens (F.)) were flown in a sustained-flight tunnel in horizontal pheromone plumes. The up-tunnel velocity of the moths increased with increasing height of flight and for G.molesta was independent of tunnel wind velocities. Use of moving ground patterns verified that the height of flight above the ground was the factor related to the changes in up-tunnel velocity. Even though up-tunnel velocity increased with increased flight height, angular velocity of image motion did not. Males appeared to use visual cues from the ground pattern and from other sources to determine their up-tunnel velocities. The relationship of preferred retinal velocities to optomotor anemotaxis is discussed.     

Effects of intermittent and continuous pheromone stimulation on the flight behaviour of the oriental fruit moth, Grapholita molesta

ABSTRACT. When male oriental fruit moths, Grapholita molesta (Busck) (Tortricidae), casting in clean air entered an airstream permeated with pheromone their flight tracks changed immediately on initial contact with pheromone, but after a few seconds returned to casting as if in clean air. The degree of change in the flight track was directly related to the concentration of pheromone. Although little net uptunnel movement occurred in response to the continuous stimulation provided by a uniformly permeated airstream, when an intermittent stimulus provided by a point-source plume was superimposed onto the permeated airstream moths were able to 'lock on' and zigzag uptunnel in the plume. The percentage of moths doing so corresponded to the difference between the peak concentration within the plume and the background concentration of pheromone permeating the airstream. Moths also locked onto, and flew upwind along the pheromone-clean-air boundary formed along a pheromone-permeated side corridor. Because a similar response was observed along a horizontal edge between a pheromone-permeated floor corridor and clean air, we conclude that the intermittent stimulation at the edge perpetuated the narrow zigzagging response to pheromone.