Swarming and mating behaviour ofChironomus flaviplumus (Diptera: Chironomidae), compared with a sympatric congeneric species,C. yoshimatsui

The swarming and mating behaviour ofChironomus flaviplumus was observed and compared with a sympatric congeneric species,C. yoshimatsui. C. flaviplumus males swarmed around sunset near foliage or angles of buildings near the emergence site and copulated with females entering the swarm. Swarming and mating occurred under conditions of higher light intensity in cooler seasons than in warmer ones. Results suggested that temperature had an effect on the timing of flight to the swarming site in both sexes. TheC. flaviplumus swarm marker and swarming behaviour seemed very similar to that toC. yoshimatsui, and their respective daily swarming time zone greatly overlapped. No mixed swarm, however, was observed in the study area. This is probably due to the distance between the species' larval habitats. Possible premating isolation mechanisms between these 2 species are discussed.     

Mating in the mosquito, Anopheles gambiae s.l.

ABSTRACT. Swarming behaviour in the Anopheles gambiae complex was observed in the field, in the Gambia, West Africa, and in the laboratory. Naturally occurring swarms of A.melas were seen in a clearing at the edge of mangrove swamps close to their breeding sites. Males could be induced to swarm over artificial 'markers' within this 'arena' but not outside it. Females were observed entering the swarm and mating. In the laboratory, in an artificial 'dusk', male A.gambiae s.str. swarmed over a black marker on the floor of their 1.2-m cube cage. In contrast to the males, females made only short flights over the marker, performing brief turning movements at its edge. It is proposed that swarming brings about the aggregation necessary before short-range attraction can take place, and that, in nature, anopheline mosquitoes orientate visually first to an arena and then to a marker within the arena. Female behaviour can be interpreted as a process of scanning possible swarm sites until mating is achieved.     

Sexual dimorphism in relation to swarming and pair formation patterns in leptocerid caddisflies (Trichoptera: Leptoceridae)

North European Leptoceridae (Trichoptera) perform three types of swarming flight patterns: (1) swarming males of Athripsodesand Ceracleafly in horizontal zigzag patterns over the water surface, (2) the Mystacidesspp. perform vertical zigzag movements, and (3) the flight of males of Triaenodes unanimisMcLach. is a mixture of the horizontal and vertical zigzagging. Also three groups of pair formation behavior can be distinguished. In the first group, of Athripsodesand Ceraclea,the females fly into the male swarms, where they are grasped and carried to the riparian vegetation by the flying males with the females hanging upside-down in genitalia coupling. In the second group, a Mystacidesfemale is caught by a male, when approaching a swarm and both use their wings to fly in tandem to the shore where they copulate. In the third group, of Triaenodes bicolor(Curt.) and Oecetis lacustris(Curt.), the males fly searching for females sitting on aquatic plants and when a female is found the male lands and they copulate immediately while clinging to the plant. The different swarming and mating behaviors might have favored selection for three types of sexual dimorphism: (1) longer forewings in males than females in species which fly in copula, (2) larger eyes in males of the vertically zigzagging species, and (3) much smaller males in the group where males search for females sitting on aquatic plants. In the second group approaching females are detected by males before reaching the swarm and in the third group the female almost always mates with the male which is the first to find her. In conclusion, we suggest that females of Athripsodesand Ceracleahave a greater choice among swarming males than do females of Mystacides, T. bicolor,and O. Lacustris.     

Swarm Site Fidelity in the Sex Role-Reversed Dance Fly Empis borealis

In the dance fly species Empis borealis (L.), females (1–40) gather to swarm at landmarks (swarm markers, like trees and bushes), and males carrying an insect prey visit these swarms for mating. We noticed earlier that some swarm sites were used for several years and that they appeared to be frequented by a similar number of swarming females in each year, although the numbers of females varied greatly among swarm sites and certain sites attracted more swarming individuals than others. To explore swarm site fidelity in this mating system, in 1993 we monitored the same swarm sites that we studied in 1989, addressing the questions, Would the same swarm sites still attract the same number of females and males after 4 years? and Why do some swarm sites attract more displaying females than others? The number of females swarming at the different markers in 1993 was approximately the same as 4 years earlier. Some of these swarm sites are known to have been used for 18 years. The swarm sites with the largest number of flies had a high sun exposure during the day and were found at coniferous swarm marker trees and in a mixed forest habitat. A swarm site with few females attending and with a low amount of insolation during the day can be predicted to be abandoned as a swarming site soon. Empis borealis swarm sites thus persist over many years and are attended by a similar number of individuals each year. To our knowledge, such site fidelity has not been demonstrated for any swarming insect species earlier.     

Swarm behaviour and mate competition in mayflies (Ephemeroptera)

Although mayfly swarms are frequently cited as an example of lekking by insects, little is known about the behaviour of individuals within a swarm, or how mate-selection takes place. A study of five species of mayfly over a period of 10 consecutive years has revealed species-specific differences in the flight pattern of swarming males and in the ability of males to recognize swarms of their own species. Males of four of the five species jostle other males in the swarm at all times except when mating: mating pairs are not jostled. The pattern of jostling varies with the species. Measurements of the sperm content of the vesicula seminalis and of the wing length of members of individual swarms show that larger wing size is positively correlated with the presence of less sperm. The vesicula seminalis is always filled with sperm at the beginning of the imaginal stage and the testes regress before the beginning of the imaginal stage. If the volume of sperm in the vesicula seminalis is a valid index of mating success then males with larger wings have the highest success. Large wings may bestow an advantage during jostling. The males of Ephemera danica , which do not jostle, glide with outspread wings; these outspread wings may attract females, the largest wings being the most attractive. Females of all five species enter the swarm a few at a time, although many females may be resting beneath the swarm. This phased entry may decrease the attraction of the swarm for predators. The number of females in a swarm is not correlated with swarm size, and the factors which enable females to regulate their entry into a swarm remain obscure.     

Acoustic orientation of male Aedes diantaeus during mating

The reaction of males of Aedes diantaeus to different auditory stimuli was studied in natural environment during swarming and under laboratory conditions. The males were attracted by 250-420 Hz that corresponds to the main frequencies of flight tones of sympatric females and the range of sensitivity of male Johnston's organs. Behavioural data show that in natural environment swarming males are attracted by flying conspecific and heterospecific females rather than by dead or immobilized females. Contact with heterospecific females always ended in parting of mosquitoes while contact with cospecific females resulted in pairing. Thus, swarming males of Aedes diantaeus localize females by their flight tones but recognize the females of their own species in contact.     

MODE OF SWARMING IN RELATION TO REPRODUCTIVE ISOLATION IN MAYFLIES

Mayfly males swarm, that is they fly in a fixed pattern by a specific object, the swarm marker. Females orientate to the same markers. Leptophlebia marginata mayflies were observed to orientate to two kinds of objects in a single locality in central Finland: to trees and to horizontal pale objects on the ground; when dispersed or moved to the other type of marker, they returned to their former orientation. Tree swarming is by far the most common mode of swarming, but some horizontally orientating populations were found. Sympatric populations are genetically and morphologically distinct, whereas other populations appear to have some gene flow between the swarming types. The tree-swarming mode appears to be primitive and the horizontal mode derived; wind rather than predation is the factor favoring swarming close to the ground. Swarming constitutes an effective mechanism of premating isolation in mayflies.     

Structure and function of the Johnston’s organ in <Emphasis Type="Italic">Fleuria lacustris</Emphasis> Kieff. males (Diptera,Chironomidae)

The majority of chironomid midges mate in swarms, where males find females by their flight sounds using specialized Johnston’s organs for acoustic perception. Males of Fleuria lacustris do not swarm and copulate on the ground. Both the flagellum and antennal fibrils are shortened and the pedicel is reduced in comparison with that typical of swarming midge species. Our results demonstrate that, in swarming midge species, the number of antennal fibrils and of A-type chordotonal sensilla in the male Johnston’s organ is by 1.33 and by 21 times higher, respectively, than in F. lacustris. Though Johnston’s organ of the latter species responds to female flight tones, it is significantly (about 70 times) less sensitive to these stimuli in comparison with the Johnston’s organ of swarming species. The decrease in the sensitivity of the Johnston’s organ in F. lacustris can be explained by the decrease in the size and the number of antennal structures, whereas their ability to perceive acoustic signals is determined by the presence of a relatively high number of A-type sensilla. Our results demonstrate that F. lacustris males are not able to search for conspecific females by perception of acoustic signals produced during the flight; however, it cannot be ruled out that females produce sounds during copulation on the substrate and thus affect male behavior.     

The More the Merrier: Swarming as an Antipredator Strategy in the Mysid <Emphasis Type="Italic">Neomysis Integer</Emphasis>

The swarming behaviour of a Baltic littoral mysid shrimp, Neomysis integer, was studied both in the presence and absence of a predator (European perch, Perca fluviatilis L.). I performed two kinds of laboratory experiments. First, the swarming tendency of mysids and the effect of swarm size on swarm choice were studied. Second, the ingestion rate of mysids was measured when feeding alone versus in a swarm. The results indicate that N. integer actively join swarms. The avoidance of the perch by N. integer individuals was stronger when there was a swarm present. Larger swarms were preferred over smaller ones regardless of presence or absence of the predator. The overall feeding rate was similar when feeding alone and in swarm, but predator cues reduced feeding rate only when the mysids were feeding alone. This study demonstrates the capability of N. integer to assess predation risk and social context and alter their behaviour accordingly.     

Feeding and sexual dimorphism in adult midges (Diptera: Chironomidae)

Adult chironomids feed readily on materials containing sucrose and glucose, and the addition of dyes is an easy way of demonstrating that food passes through the gut. Male and female flies are shown to make very different use of the food they take in. Males show no change in longevity but extend their flight time for an average of 160% over unfed males. Females, by contrast, show no detectable increase in flight time, but increase longevity by about 40%. Sexual dimorphism in the use of food seems appropriate to the roles of the sexes. We infer that males improve their swarming performance while females may benefit from increased longevity both in gaining time to find suitable mates and in the distance dispersed after mating. Males, and to a less extent females, are found on aphid infested trees near fresh water, and the suggested biological value of feeding is in sustaining the swarming flight especially for the males. Trichoptera adults are found feeding on aphid infested trees and the earlier findings that adult Trichoptera feed are confirmed.     

Nuptial flights and calling behaviour in the antLeptothomx acervomm (Fabr.)

Summary We describe in detail a very large nuptial flight of the antLeptothorax acervorum at an open hilltop site in Britain. The mating behaviour of these ants involved not only a large mating swarm but also sexual/calling behaviour by the females. The females left the flight to land on vertical objects, where they took up a characteristic calling posture, in which females of closely related species are known to release pheromones that are sexually attractive to males. ThatLeptothorax acervorum has a complex mating behaviour involving both large nuptial flights and sexual calling has important consequences for the interpretation of the evolution of polygyny in this species and social parasitism in its close relatives.     

Swarming and mating of Aedes communis mosquitoes in nature

The date of the beginning of mating behaviour in males and females, the rate of insemination and the increasing of bloodsucking activity of females were studied in natural environments. Over 80% of females mated on the 3-4th day after emergence; after fertilization their behaviour changed from looking for males for coupling to looking for ones for a prey. The male swarming began on the 5th day after emergence and simultaneously the appearance of inseminated females was observed. The places of mating of males and females were investigated. It was established that coupling took place in swarms with swarming males and out of swarms with freely flying males.     

Olfactory orientation responses of the eucalyptus woodborer, Phoracantha semipunctata, to host plant in a wind tunnel

The eucalyptus woodborer, Phoracantha semipunctata Fabricius (Coleoptera: Cerambycidae), attacks mainly species of Eucalyptus (Myrtaceae). This study investigated walking and flight behaviour of P. semipunctata males and females exposed to an odour plume originating from a log of E. globulus placed vertically in the upwind end of a wind tunnel. In control experiments, beetles were exposed to a PVC drainpipe in the same position as the log, providing a visual stimulus without host‐tree odour. No statistical differences were found between behavioural responses of either sex when exposed to the log or PVC pipe. No beetles landed on the PVC pipe, whereas 49% of the beetles exposed to host‐tree odour plume landed on the log. Beetles aged over 24 days after emergence from the host tree were more responsive than beetles aged 20–24 days, and accounted vor 86% of the beetles that landed on the log. While walking, host‐tree odour affected the behaviour of the beetles that landed on the log as follows: upwind movement and path linearity increased, whereas turning rate, stopping frequency, mean stopping time and time to take‐off flight decreased. During flight, host‐tree odour affected the behaviour of the beetles that landed on the log as follows: increased upwind flight, turning rate, flight time, flight distance, and decreased flight speed. For beetles that never lost contact with the odour plume, flight progressed upwind with narrow zigzags, and showed higher directedness upwind, path linearity, faster flight speed and lower turning rate than for beetles that lost contact with the odour plume. After loosing contact with the plume, beetles tended to decrease their upwind progression, exhibiting a sharp turn or quick counterturns followed by crosswind or downwind excursions. This led to regaining contact with the odour plume and resumed upwind progression at higher speed provided they flew within the boundaries of the plume. The results showed that host‐tree odour affects both walking and flight behaviour of P. semipunctata beetles, inducing a more directed upwind movement and landing on the visual stimulus of a tree trunk.     

Widespread 'hilltopping' in Acraea butterflies and the origin of sex-role-reversed swarming in Acraea encedon and A. encedana

In some populations of the butterflies Acraea encedon and A. encedana, most females are infected with a bacterium that kills their sons. The resulting shortage of males is associated with females adopting a sex‐role‐reversed mating system, in which females swarm at landmarks such as hilltops and compete for males. We have observed the mating behaviour of Acraea species that are not known to be infected with the male‐killer. In over half of these species, males were found to aggregate on hilltops. It is likely that this behaviour was ancestral to the sex‐role‐reversed swarms of Acraea encedon and A. encedana, and we discuss how the spread of the male‐killing infection may have converted this mating system into sex‐role‐reversed swarming.     

Odour-mediated upwind flight of Culex quinquefasciatus mosquitoes elicited by a synthetic attractant: a reappraisal

Abstract. Pile et al. (1991) report that the putative oviposition attractant ace-toxyhexadecanolide has four effects on gravid females of Culex quinquefasciatus Say: (1) it induces upwind anemotaxis, (2) near to an oviposition site it evokes an orthokinetic slowing of flight speed plus (3) a klinokinetic increase in turning rate, and (4) it causes females to stay longer at oviposition sites. This reappraisal shows that the first two of these conclusions are supported by the evidence provided but the second two are not.     

Interactions Between Swarming Chironomus annularius (Diptera: Chironomidae) Males: Role of Acoustic Behavior

Males of swarming species of chironomids use their auditory system (Johnston's organs) to recognize a female within swarm and do not respond to male flight tones. However, in some cases the male–male interactions were observed at a high frequency. The role of acoustic behavior in this phenomenon in C. annularius was studied. The results showed that male Johnston's organs were sensitive to male flight tones from a distance of about 1–1.5 cm. The carrier frequencies of these sounds negatively correlated with male body size. Thus we would expect that male–male interactions will occur mainly between large males. Nonetheless, the analysis of caught pairs revealed that in both male–male and female–male interactions small males had an advantage. The ability of males to perceive the male flight tones is discussed with respect to swarming behavior and mating success.     

Foraging and mate-finding in the silver Y moth, Autographa gamma (Lepidoptera: Noctuidae) under the risk of predation

Animal foraging and reproductive behaviour is influenced by other simultaneous demands such as predator avoidance. The trade-offs between these demands may depend on sex or mating experience. This study demonstrates that the olfactory-mediated foraging and mate-seeking behaviours in the silver Y moths, Autographa gamma , are affected by auditory cues mimicking their bat predators. Both males and females changed their foraging behaviour under simulated predation risk. Fewer moths reached the odour source following sound stimulation and the time to find the odour source increased by up to 250%. However, there were no significant differences between male and female ability to reach the plant odour source or the duration of the flight towards the source when stimulated with ultrasound. Hence females are not more cautious than males when observed in the same behavioural context. Risk-taking in males was independent of whether they were flying toward a flower odour or sex pheromones having equal attractive value. This indicates that the trade-off between olfactory and acoustic cues is independent the type of odour. Mated females were not as strongly affected by sound as non-mated, indicating that flower odours have a higher adaptive value for mated females, suggesting that some processes following mating experience influence the trade-off between flower odours and simulated bat sounds.     

Swarming Behavior, Sexual Dimorphism, and Female Reproductive Status in the Sex Role-Reversed Dance Fly Species Rhamphomyia marginata

Dance flies are predaceous insects which often form male mating swarms. In many species males prior to swarming catch an insect prey, which is presented to the female at mating. In Rhamphomyia marginata, females in contrast to males gather to swarm, while males carrying a prey visit swarms for mating. Here I describe the swarming and courtship behavior in R. marginata and provide data on sexual dimorphism and swarming female reproductive status. Females swarm in small clearings in the forests. There was no specific swarm-maker. The swarming period lasted for 2–3 h and peaked around sunset. Identical swarm sites were used each evening and for several years. The mean number of females in swarms (swarm sites with at least one female) was 9.9 ± 9.1 (range, 1–40; n = 107) in 1993 and 7.1 ± 7.0 (range, 1–35; n = 68) in 1994. No obvious competition between females in swarms was observed. The operational sex ratio in swarms was extremely female biased (all swarms, 0.04). Less than one-third of male visits to swarms resulted in mating and males were found more often in larger swarms. Nuptial prey consisted of male midges. Females seem to mate more than once. Swarming females had undeveloped eggs, whereas mated females in swarms had further developed eggs than unmated females. Amount of sperm in the spermatheca was correlated with egg size. Amount of sperm and egg size did not correlate with wet weight, wing length, or wing load, except for egg size and weight. The wing coloration pattern and shape in R. marginata females are unique among dance flies, being greatly enlarged (1.6 times larger than that of males) and bicolored (gray part, 60% of wing area). When females, instead of males, possess extravagant secondary sexual characters, it is predicted from sexual selection theory that females should compete for males and that males should be selective in their choice of partner. A sex-role reversal will evolve when assess to males limit female reproductive success. The dance fly species R. marginata, like Empis borealis, another dance fly species studied earlier and discussed here, seems to fit these predictions.     

Low-Frequency Sounds Repel Male Mosquitoes <Emphasis Type="Italic">Aedes diantaeus</Emphasis> N.D.K. (Diptera,Culicidae)

We experimentally demonstrated that tonal acoustic signals with a carrier frequency of 140–200 Hz had a repellent effect on male mosquitoes (Culicidae). Swarming males of Aedes diantaeus were concentrated in a small space near the auxiliary attracting sound source which simulated the flight sound of conspecific females (carrier frequency 280–320 Hz). Then, the resulting cluster of attracted mosquitoes was stimulated with test signals of variable amplitude and carrier frequency from a second loudspeaker. The direction of mosquito flight from the source of test sounds and a decrease in their number above the attracting sound source were used as the criteria of behavioral response. Pronounced avoidance responses (negative phonotaxis) of swarming mosquitoes were observed in the range of 140–200 Hz. Most of the mosquitoes left the area above the attracting sound source within one second after the onset of the test signal. Mosquitoes mostly flew up, sideways, and backwards in relation to the test acoustic vector. We presume that mosquitoes develop defensive behavior against attacking predatory insects based on analysis of auditory information. The range of negative phonotaxis is limited at higher frequencies by the spectrum of the flight sounds of conspecific females, and in the low frequency range, by the increasing level of atmospheric noise.     

Age-associated male mating success in three swarming caddis fly species (Trichoptera: Leptoceridae)

Abstract. 1. In the three caddis fly species, Athripsodes albifrons (L.), A. cinereus (Curtis) and Mystacides azurea (L.) (Leptoceridae; Trichoptera), males swarm above the water surface of lakes or rivers. Receptive females fly to swarms and are chased and/or courted by males. After one of the swarming males has grasped an approaching female, the pair flies in tandem to the shore where they copulate.
2. In males, wing wear indices were negatively correlated with the ratio of fat/dry weight. In the only species in which comparisons were possible between newly emerged and swarming males (M. azurea), the former had significantly lower indices. Unmated females on average had lower wing wear indices than spent females. These facts suggest that wing wear reflects relative age.
3. The tandem males had significantly less wing wear than those in swarms, and are probably therefore younger. Age is therefore likely to be significant in relation to mating success.
4. Among males of the same relative age, tandem males had higher fat ratio than swarming ones, indicating that male mating success was also influenced by traits other than age. It is suggested that the shortest possible duration of the period of adult prematurity is adaptive, especially in insects with marginal adult food intake.