Male courtship song in circadian rhythm mutants of Bactrocera cucurbitae (Tephritidae: Diptera)

Role of the clock gene period in regulating circadian rhythm of courtship vibrations in Nilaparvata lugens

Nilaparvata lugens, the brown planthopper (BPH), is a notorious pest threatening rice production across Asia. The heavy reliance on synthetic insecticides for control has led to resistance and raised ecological concerns. Substrate-borne vibrational communication, integral to species-specific mate recognition systems in insects, presents a potential avenue for pest management through mating disruption. However, the molecular mechanisms regulating vibrational signals in BPH remain poorly understood. In this study, we cloned and analyzed the clock gene period from BPH. The open reading frame of Nlper is 3708 bp, encoding a 1235-amino acid protein with two conserved domains: the Per-ARNT-Sim domain and the Period protein 2/3C-terminal region. It shares a closer evolutionary relationship with Laodelphax striatellus and Frankliniella occidentalis. Spatiotemporal expression analysis showed that Nlper was consistently expressed across all life stages and adult tissues, with the highest levels in macropterous males and male head, respectively. Rhythmic expression exhibited significant circadian oscillations under both light-dark and constant darkness conditions, peaking at 00:00 and reaching a trough at 12:00, with fold changes ranging from 2.47 to 3.39. Moreover, after dsRNA injection, Nlper expression decreased by 77.21%-84.26% from day 2 to day 5, disrupting the circadian oscillation of female vibrational signals (FVS) and causing a significant peak shift, along with a 30.56% reduction in FVS frequency on day 5. These findings underscore the essential role of Nlper in regulating the circadian rhythm of courtship vibrational signals, deepening our understanding of the genetic basis of insect communication and opening new possibilities for innovative pest management approaches.

Acoustic characteristics of sound produced by males of Bactrocera oleae change in the presence of conspecifics

Males of the olive fruit fly Bactrocera oleae vibrate and stridulate their wings at dusk producing sounds different from flight sounds with no confirmed behavior role. We recorded and performed a temporal-spectral analysis of this sound. Sound produced by male wing vibration/stridulation consists of intermittent pulses of highly variable duration and of fundamental frequency of around 350 Hz. Flight sound has a much lower fundamental frequency of approximately 180 Hz. Males begin to display wing vibration and sound production at the beginning of their sexual maturity at the 5th day of their age. This behavior is more pronounced in the presence of another conspecific male and observed less in male–female pairs or in solitary males. Broadcasts of the recorded sound did not attract flies of either sex. The highest fundamental frequency was found in association with wing vibrations emitted by male–male pairs, followed by those emitted by male–female pairs and then solitary males, which showed the lowest frequency values. The mean pulse duration and interpulse interval were shorter in male–male pairs than in male–female pairs. We assume that the male wing vibration and the produced signal, apart from its possible role in the courtship of the females, could also be associated with male–male interactions for territorial and rival activities, for which further experiments are required.

Courtship rhythm in Nasonia vitripennis is affected by the clock gene period

The clock gene period (per) is a regulator of circadian rhythms but may also play a role in the regulation of ultradian rhythms, such as insect courtship. Males of the parasitoid wasp Nasonia vitripennis court females by performing series of head movements (‘head-nods’) and wing vibrations within repeated cycles. The pattern of cycle duration and head-nod number is species-specific and has a genetic basis. In this study, the possible involvement of per in regulating Nasonia courtship rhythms was investigated in a southern and northern European strain that differ in number and timing of courtship components. Knockdown of per via RNA interference (RNAi) resulted in a shortening of the circadian free running period (tau) in constant darkness (DD), and increased both the cycle duration and the number of head-nods per cycle in both strains. These results point at a role of per in the regulation of ultradian rhythms and male courtship behaviour of N. vitripennis and may contribute to resolving the controversy about the role of per in insect courtship behaviour.

Mating-induced changes in responses of female Queensland fruit fly to male pheromones and fruit: A mechanism for mating-induced sexual inhibition

In order to reproduce, female tephritid fruit flies need both mates for fertilization and fruit for oviposition. Virgin females are prone to mating and approach males, attracted by their pheromones. Mated females, however, may experience an abrupt reduction of mating propensity and prioritise the search for suitable fruit rather than additional mates. Accordingly, mating in fruit flies may induce a switch in olfactory preferences of females from pheromones to fruit stimuli, and this switch may also be an important mediator of mating-induced sexual inhibition. To test for mating-induced switches in olfactory preference of female Queensland fruit fly, Bactrocera tryoni, we used wind tunnel assays to assess attraction of mated and virgin females to (1) male sex pheromone delivered through a perforated glass sphere or (2) an entire fruit. Electroantennogram (EAG) responses were also used to test for mating-induced changes in olfactory sensitivity to pheromones and fruit odours. Pheromones elicited quicker upwind responses in virgin females than in mated females; during the first six minutes of trials more virgin females than mated females were observed in the upwind end of the wind tunnel where pheromone odours were released. Fruit cues, in contrast, elicited stronger association with the upwind end of the wind tunnel in mated females than in virgin females from the fifth minute onwards. Also, mated females were observed on the fruit for longer periods than virgin females. EAG responses to pheromones and fruit odours were similar in virgin and mated females, indicating that changes in preferences are not a consequence of changes in peripheral sensitivity of antennae to odours but instead appear to be mediated by post-receptor processing. Our results show that mating reduces attraction to male-produced pheromones and increases attraction to fruit stimuli in B. tryoni females. We propose that this behavioural switch from mating stimuli to oviposition stimuli is an important mediator of mating-induced sexual inhibition in this species.

Circadian rhythms and period expression in the Hawaiian cricket genus Laupala

Daily activity times and circadian rhythms of crickets have been a subject of behavioral and physiological study for decades. However, recent studies suggest that the underlying molecular mechanism of cricket endogenous clocks differ from the model of circadian rhythm generation in Drosophila. Here we examine the circadian free-running periods of walking and singing in two Hawaiian swordtail cricket species, Laupala cerasina and Laupala paranigra, that differ in the daily timing of mating related activities. Additionally, we examine variation in sequence and daily cycling of the period (per) gene transcript between these species. The species differed significantly in free-running period of singing, but did not differ significantly in the free-running period of locomotion. Like in Drosophila, per transcript abundance showed cycling consistent with a role in circadian rhythm generation. The amino acid differences identified between these species suggest a potential of the per gene in interspecific behavioral variation in Laupala.

Two distinct genomic regions, harbouring the period and fruitless genes, affect male courtship song in Drosophila montana

Acoustic signals often have a significant role in pair formation and in species recognition. Determining the genetic basis of signal divergence will help to understand signal evolution by sexual selection and its role in the speciation process. An earlier study investigated quantitative trait locus for male courtship song carrier frequency (FRE) in Drosophila montana using microsatellite markers. We refined this study by adding to the linkage map markers for 10 candidate genes known to affect song production in Drosophila melanogaster. We also extended the analyses to additional song characters (pulse train length (PTL), pulse number (PN), interpulse interval, pulse length (PL) and cycle number (CN)). Our results indicate that loci in two different regions of the genome control distinct features of the courtship song. Pulse train traits (PTL and PN) mapped to the X chromosome, showing significant linkage with the period gene. In contrast, characters related to song pulse properties (PL, CN and carrier FRE) mapped to the region of chromosome 2 near the candidate gene fruitless, identifying these genes as suitable loci for further investigations. In previous studies, the pulse train traits have been found to vary substantially between Drosophila species, and so are potential species recognition signals, while the pulse traits may be more important in intra-specific mate choice.

Genetically regulated temporal variation of novel courtship elements in the Hawaiian cricket genus Laupala

The Hawaiian cricket genus Laupala (Gryllidae: Trigonidiinae) has undergone rapid and extensive speciation, with divergence in male song and female acoustic preference playing a role in maintaining species boundaries. Recent study of interspecific differences in the diel rhythmicity of singing and mating, suggests that temporal variation in behavior may reduce gene flow between species. In addition, Laupala perform an elaborate and protracted courtship, providing potential for further temporal variation. However, whether these behavioral differences have a genetic basis or result from environmental variation is unknown. We observed courtship and mating in a common garden study of the sympatric species, Laupala cerasina and Laupala paranigra. We document interspecific differences in the onset and duration of courtship, spermatophore production rate, and diel mating rhythmicity. Our study demonstrates a genetic contribution to interspecific behavioral differences, and suggests an evolutionary pathway to the origins of novel timing phenotypes.

C. elegans homologs of insect clock proteins: a tale of many stories

As a consequence of the Earth's axial rotation, organisms display daily recurring rhythms in behavior and biochemical properties, such as hormone titers. The neuronal system controlling such changes is best studied in the fruit fly Drosophila melanogaster. In the nematode worm Caenorhabditis elegans, most homologs of these genes function in the heterochronic pathway controlling the (timing of) developmental events. Recent data indicate that in the worm at least one of the genes involved in developmental timing is also active in circadian rhythm control, thereby opening up new perspectives on a central (neuronal) timer interfering with many processes. Also, new neuropeptidergic clock homologs have been identified in nematodes, supporting the idea of a broad range of clock-regulated targets. We will describe the current knowledge on homologous clock genes in C. elegans with a focus on the recently discovered pigment dispersing factor gene homologs. Similarities between developmental and daily timing are discussed.