Calling Behavior and Sex Pheromone Release and Storage in the Moth Chloridea virescens

Temporal characteristics of turbulent flow and moth orientation behaviour patterns with fluent simulation and moth-based moving model simulation

Objective

Previous research has explored the pheromone release patterns of female moths, revealing species-specific release frequencies and the transmission of temporal information through odourant plumes in turbulent flows. Varying the release frequency during the orientation process results in distinct orientation behaviours. Studies on moth movement patterns have determined that encounters and deviations from odour plumes elicit distinct reactions; the time interval between each movement pattern is measured as the "reaction time," and the interval between each detection and loss of odourant plume is measured as the "gap length."

Methods

We simulated turbulent flow at various release frequencies. Our efforts focused on establishing a model that could simulate the joint orientation movement under turbulent flow and intermittent plumes. We built an agent moving mechanism, including wind velocity information, with particular reference to the temporal parameter and orientation success efficiency.

Results

We calculated the time threshold of each burst in different simulations under different wind velocities and release frequencies. The time structure characteristics of the plume along the turbulent flow vary depending on the distance from the source. We simulated walking agents in a turbulent environment and recorded their behaviour processes. The reaction time, release interval, and time threshold were related to the orientation results.

Conclusion

On the basis of previous experimental results and our simulations, we conclude that the designated interval time likely enhances search efficiency. The complex and dynamic natural environment presents various opportunities for using this unique odour-source searching capability in different scenarios, potentially improving the control systems of odour-searching robots.

Reinvestigation of sex pheromone biosynthesis in the moth Trichoplusiani reveals novel quantitative control mechanisms

Many species of moths have a common control mechanism for synthesizing sex pheromone: the circadian release of pheromone biosynthesis-activation neuropeptide (PBAN) that switches pheromone synthesis on/off during the day. One apparent exception to this is the noctuid moth Trichoplusia ni (Hübner), in which pheromone synthesis appears continuous through the photoperiod, with circadian release of PBAN controlling emission rate of pheromone during calling. Sex pheromone biosynthesis was reinvestigated in T. ni using stable isotope tracer-tracee and gland sampling techniques to ascertain how pheromone quantities in gland cells and on the gland cuticular surface varied and were controlled. It was found that (i) carbohydrate from adult female feeding is used to synthesize sex pheromone, (ii) most of the stored acetate ester pheromone component(s) is contained in gland cells, (iii) a large pool of pheromone is synthesized and stored through the photoperiod with a slow turnover rate, (iv) although pheromone is synthesized throughout the photoperiod, its rate can vary, influenced by release of PBAN and possibly by an unidentified head factor, with both affecting carbohydrate uptake into the acetyl CoA pheromone precursor pool, and (v) as suggested previously, PBAN also influences translocation of pheromone out of the cell to the cuticular surface, possibly by causing breakdown of intracellular lipid droplets storing pheromone molecules. This work suggests that the quantitative synthesis and emission of pheromone in T. ni, and possibly other moths, is regulated by multiple complementary biochemical mechanisms.

Some Factors Influencing Calling Behavior and Mass Emission Rate of Sex Pheromone from the Gland of the Moth Chloridea virescens

To attract a mate, females of most moth species synthesize and emit sex pheromone from a specific gland in a behavior termed "calling". In a broad temporal sense, calling behavior and pheromone synthesis are synchronized through the overlap of their circadian rhythms. However, the limited amount of pheromone a female produces each day must be managed so that pheromone is emitted at a sufficient (to attract males) mass emission rate (MER) over the entire calling period, typically many hours. We are studying pheromone synthesis and emission in the moth Chloridea (formerly Heliothis) virescens (family Noctuidae). One way that female C. virescens manage pheromone over their calling period is by calling intermittently; the period between calling bouts allows females to replenish pheromone, and resume calling at high MERs. However, militating against replenishment is loss of pheromone through putative catabolism. In this paper, we examined three aspects pertaining to pheromone MER in C. virescens: (i) the effect of adult feeding on calling behavior, (ii) the effect of certain behavioral/physical parameters on MER, and (iii) the relative loss (putative catabolism) of pheromone in retracted (non-calling) and everted (calling) glands. We found that (i) adult feeding increases calling duration, consistent with the known concomitant increase in pheromone production, (ii) various physical factors relating to the gland, including degree of eversion (surface area), orientation to airstream, and air velocity over the gland influence MER, and (iii) putative catabolism occurs in both retracted and everted glands, but substantially less pheromone is lost in the everted gland primarily because of the high MER when the gland is first everted. Together, these data demonstrate that, over the calling period, the efficient use of pheromone for emission by female C. virescens is dependent on the interaction among synthesis, storage, catabolism, and calling behavior.

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

Many insect species have circadian rhythms of pheromone production/titer, calling, emission, and response that are involved in intraspecific communication and impact pest management practices. Rhythms of pheromone biosynthesis, most studied in moths affecting forestry and agriculture, contribute to a periodicity of pheromone concentration or titer within glands or hemolymph. Calling rhythms by the pheromone-emitting sex are physical movements (pumping, vibrating wings) that aid in release and dispersion of the volatile pheromone components attractive to the opposite conspecific sex or both sexes. Circadian rhythms of emission of pheromone also occur as a result of an interaction between calling and the titer of pheromone available for release. Responding individuals usually show a coincidental rhythm of dispersal flight while seeking pheromone plumes in which, by orienting upwind, the insects find mates or food resources. However, some species begin searching an hour or more before the emitting sex initiates calling and emission, which benefits mass trapping control programs because the baited traps do not compete initially with natural pheromone sources. In our review, data of daily rhythms of moths and other insects were extracted from the literature by screen capture software to calculate mean time of activity and standard deviation and fit to normal curves. These methods are illustrated for various insects and as a basis for discussion of interactions of pheromonal circadian rhythms of the well-studied gypsy moth Lymantria dispar, spruce budworm moth Choristoneura fumiferana, turnip moth Agrotis segetum, and cabbage looper moth Trichoplusia ni. The various circadian rhythms are discussed in relation to application of species-specific sex and aggregation pheromones for benign biological control and management of pest insects.

Sex pheromone biosynthesis, storage and release in a female moth: making a little go a long way

Moth pheromone research has pioneered much of our understanding of long-distance chemical communication. Two important characteristics of this communication have, however, remained largely unaddressed: the release of small quantities of pheromone by most moth species, despite potential advantages of releasing greater amounts, and the intermittency of release in some species, limiting the time of mate attraction. We addressed the proximate mechanisms underlying these characteristics by manipulating biosynthesis, storage and release of pheromone in females of the noctuid moth Chloridea virescens. We found that (i) mass release is determined by pheromone mass on the gland surface; (ii) amounts synthesized are limited by pheromone biosynthesis activating neuropeptide concentration, not precursor availability; (iii) some gland structural feature limits mass release rate; (iv) intermittent calling enables release at a mass rate greater than biosynthetic rate; and (v) at typical mass release rates, the periodicity of pheromone availability on the gland surface roughly matches the periodicity (intermittency) of calling. We conclude that mass release in C. virescens and possibly many other species is low because of constraints on biosynthesis, storage and gland structure. Further, it appears the behaviour of intermittent calling in C. virescens may have evolved as a co-adaptation with pheromone availability, allowing females to release pheromone intermittently at higher mass rates than the biosynthesis rate.

The Effect of Pheromone Synthesis and Gland Retraction on Translocation and Dynamics of Pheromone Release in the Moth Chloridea virescens

Most species of moths use a female-produced sex pheromone to bring mates together. Typically, sex pheromone is synthesized in a specialized gland and released during the behavior of "calling", in which the ovipositor and gland are extruded, allowing pheromone to evaporate. Although there has been much study on how a gland makes specific pheromone components, we know relatively little about how it actually functions with regard to synthesis, storage and release. In this paper, we investigated three aspects of gland function in the noctuid moth Chloridea virescens (Fabricius): (i) whether translocation of pheromone from site of synthesis to release is dependent on calling or ovipositor movement, (ii) whether pheromone synthesis rate limits release and (iii) how intermittent calling (observed in this and other species) might affect the dynamics of release rate. Firstly, by manipulating the gland to simulate calling (extruded) or non-calling (retracted), we showed that pheromone translocation occurred regardless of whether the gland was retracted or extruded. Secondly, by manipulating pheromone production, we found that females that produced more pheromone had higher release rates. It was especially noticeable that females had a higher release rate at the start of calling, which dropped rapidly and leveled off over time. Together, these data suggest that intermittent calling in C. virescens (and other species) may function to allow females to replenish pheromone stores on the gland surface between calling bouts, so that brief, high release rates occur at the start of a calling bout; thus, potentially increasing a female's chances of attracting a mate.

Challenges in Modeling Pheromone Capture by Pectinate Antennae

Insect pectinate antennae are very complex objects and studying how they capture pheromone is a challenging mass transfer problem. A few works have already been dedicated to this issue and we review their strengths and weaknesses. In all cases, a common approach is used: the antenna is split between its macro- and microstructure. Fluid dynamics aspects are solved at the highest level of the whole antenna first, that is, the macrostructure. Then, mass transfer is estimated at the scale of a single sensillum, that is, the microstructure. Another common characteristic is the modeling of sensilla by cylinders positioned transversal to the flow. Increasing efforts in faithfully modeling the geometry of the pectinate antenna and their orientation to the air flow are required to understand the major advantageous capture properties of these complex organs. Such a model would compare pectinate antennae to cylindrical ones and may help to understand why such forms of antennae evolved so many times among Lepidoptera and other insect orders.