Influence of Predator Presence and Prey Density on Behavior and Growth of Damselfly Larvae (Ischnura elegans) (Odonata: Zygoptera)

Foraging behavior is often determined by the conflicting benefits of energy gain and the risk of mortality from predation or other causes. Theory predicts that animals should have lower activity levels when either the risk of predation or the availability of resources in the environment is high. We investigated the adjustment of the behavior of I. elegans larvae to predator presence (Anax imperator) and prey density (Daphnia sp.) and their interaction in a completely crossed factorial experiment in the lab and the effect of behavior on growth. The foraging activity of the I. elegans larvae was significantly reduced in the presence of a free-swimming predator but not a caged predator. Abdominal movements were significantly reduced at a low prey density. Growth was significantly reduced by the presence of a free swimming predator and low prey densities. These results provide evidence that these damselfly larvae adjust their behavior to the presence of predators to increase their survival at the expense of reduced growth and development.     

Visual Cues in Mate Recognition by Males of the Damselfly, Coenagrion puella (L.) (Odonata: Coenagrionidae)

Coenagrion puella males search actively for mates and are not aggressive to other males. To study the role of visual cues in male–female discrimination, four types of models were used: (1) bodies of intact insects, (2) models of painted males, (3) models of male–female chimerae, and (4) models of female body parts. Abdomen coloration pattern and presence of wings were the most important cues for sexual recognition by males. Step-by-step elimination of male coloration pattern leads to an increase in the tandem response rate. A female model painted as a male repelled males like the intact male model. The absence of either the head or the thorax slightly decreased the number of tandem responses, but models without both the head and the thorax were not recognized as a mate. Abdomen thickness larger than that of a normal female decreased the attractiveness of the model. Models of the gynochrome female were significantly more attractive than models of the androchrome one. Female models containing male parts were less attractive than models without any structure at this place. Using principal-components analysis, it is shown that models repelling males usually were those containing an intact male abdomen or a female abdomen painted with blue. The results indicate that C. puella males can distinguish males from females visually by morphological structures and coloration pattern.     

Function of abdomen wave behavior in larvalischnura verticalis (Odonata: Coenagrionidae)

Odonate larvae are important predators in the littoral zone of freshwater systems, and in an effort understand their population dynamics, researchers have described and analyzed many of their behaviors. The behavior we call abdomen wave has been considered to be both an aid to respiration and an aggressive display to conspecifics. We found that, under laboratory conditions, abdomen wave was not increased when the oxygen concentration was low or when larvae were in the presence of conspecifics. These results suggest the behavior is not involved in oxygen uptake or in agonistic interactions. The behavior was increased when larvae had food in their guts and was most dramatically increased in the hours preceding a molt. Abdomen wave may function to loosen the exoskeleton prior to molting and/or release of metabolites.     

Isolation and characterization of microsatellite loci to study parthenogenesis in the citrine forktail,Ischnura hastata (Odonata: Coenagrionidae)

The citrine forktail, Ischnura hastata, is an American damselfly species, widely distributed, with only‐female populations also found at the Azores islands. Here we report the development of nine microsatellite loci for this species. The number of alleles per locus ranged from six to 11, with an observed heterozygosity ranging from 0.245 to 0.737. Eight of the nine loci successfully amplified in a sample of parthenogenetic females from the Azores. The developed microsatellite system will be a useful tool to investigate population structure, as well as the number of clones, the type of parthenogenesis and the origin of the parthenogenetic populations of this species.     

Starvation and the Mating Success of Wild Male Mediterranean Fruit Flies (Diptera: Tephritidae)

Recent evidence suggests that the nutritional state of male Mediterranean fruit flies, Ceratitis capitata (Wied.) (medfly), is an important influence on various components of their reproductive biology, including mating success. The objective of the present study was to examine experimentally the effect of temporary starvation on the mating success of wild male C. capitata. Males were maintained on protein–sugar or sugar-only diets, and for each diet we compared the mating success of continuously fed males versus males starved for 18 or 24 h immediately before testing. In trials conducted on field-caged, host trees, males starved for 24 h obtained only about half as many matings as fed males for both diets. However, when the starvation period was 18 h, starved males reared on the protein–sugar diet mated significantly less frequently than fed males, whereas starved males reared on sugar mated as often as fed males. Measurements of male pheromone calling and female attraction revealed that reduced mating success likely reflected the decreased signaling activity of starved males.     

Differences in adult and reproductive lifespan in the two male forms ofMnais pruinosa costalis selys (Odonata: Calopterygidae)

The damselflyMnais pruinosa costalis (Odonata: Calopterygidae) is unusual in that males are dimorphic, existing as clear-winged non-territorial ‘sneaks’ and orange-winged territorial ‘fighters’. Here we report the results of population census data and behavioural observations in the field and laboratory, and present estimates of emergence period, reproductive period, total lifespan, and reproductive success of each morph. Clear-winged males are smaller and have lower daily reproductive success than orange-winged males, but live for longer in the field and laboratory. We accounted for the difference in the ‘operational reproductive life’ of the two morphs and estimated lifetime reproductive success: there was no difference between clear-winged and orange-winged males. We discuss possible mechanisms for the maintenance of the two forms.     

Postcopulatory Behavior in Libellula pulchella Drury (Odonata: Libellulidae) and Female Tactics for Avoiding Male Interference with Oviposition

Postcopulatory behavior was studied in Libellula pulchella, a North American dragonfly in which ovipositing females face frequent harassment by unpaired males seeking matings. Although males performed noncontact guarding of their mates after copulation, females received minimal protection since their guarders tended to leave on extended chases of other males when harassment was intense. Ovipositions by unguarded females were even more likely to be terminated by harassment and were disrupted sooner. Female tactics to minimize interference included rapid escape flights, repeated return visits to the water within short time periods, perching when severerly harassed, and proceeding with mating when clasped. Female use of multiple oviposition sites is discussed in the context of guarding effectiveness and mate recognition by males.     

Larval morphology and range of three West Asiatic species of the genus Onychogomphus Selys, 1854. (Insecta: Odonata)

The previously unknown larvae of O. assimilis (Schneider, 1845) and O. lefebvrei (Rambur, 1842) are described, while that of O. flexuosus (Schneider, 1845) is redescribed, all from material from SW. Turkmenistan and Tajikistan. Their distributions extend from the eastern mediterranean to central-west Asia and are mapped. A differential diagnosis and key to the identification of the larvae of four central Asiatic species of the genus Onychogomphus is given.     

The mating system ofBrechmorhoga pertinax (Hagen): The evolution of brief patrolling bouts in a “territorial” dragonfly (Odonata: Libellulidae)

Males of Brechmorhoga pertinax(Hagen) patrolled and competed for narrow strips of stream edge, 2–8 m long, containing a few barely submerged patches of sandy or fine gravel substrate. These scarce patches were used as oviposition sites by females that usually, but not always, mated with a patrolling male just prior to egg-laying. Females visited the oviposition sites evenly throughout the day from 0830 to 1430 but male activity rose until midday and then declined sharply after 1330. Some gravid females refused to mate in the midafternoon despite male efforts to copulate with them. The average patrolling bout by a male lasted less than 15 min, with defenders usually leaving immediately after one or two aggressive interactions with intruders or leaving voluntarily without apparent cause. Many individuals returned for additional bouts of patrolling at the same site, but the total daily period of patrolling for any one individual almost never exceeded 1 h.     

Influences on variation in territorial tenures of male white-faced dragonflies (Leucorrhinia intacta) (Odonata: Libellulidae)

Some individuals in species with extended periods of territorial occupancy may change territory locations within a single bout of territorial activity. Length of occupancy of mating territories among males in a local population of white-faced dragonflies (Leucorrhinia intacta) varied from more than 6 h to 15 min or less. Males with short tenures often established territories in several locations on the pond during a day. Several hypotheses have been proposed to explain shifting territorial sites rather than remaining in a single site during one bout of territoriality. We attempted to test the hypothesis that males shift to leave low-quality sites. Site quality may be affected by costs of defense in relation to intruder rate and the mating benefits of holding the territory. To test whether variation in these possible effects of benefits and costs of territoriality influenced tenure, we manipulated local quality of oviposition substrate and perch density. The quality of oviposition substrate, but not perch density, influenced both potential benefits and costs of territoriality. Female density was higher in areas with good substrate, but so were rates of males intruding into the territories, rates of chasing by territorial males, and local density of territorial males. More matings occurred in areas with good substrate, but among males with tenures of 15 min or more, mating success per male and tenure lengths did not differ statistically among treatments. Defense costs were low for all treatments and perhaps were not an important influence on tenure duration. Territorial males in this population probably adjusted local density to expected mating success by initial choice of site rather than by varying tenure length. Variation in tenure length at a site resulted, in part, from stochastic external factors, such as predation attempts.     

Multiple Mating and Reproductive Success of Male and Female Apple Maggot Flies, Rhagoletis pomonella (Diptera: Tephritidae)

Mature male and female apple maggot flies mated frequently on a field-caged host tree during a 14-day study. Each sex averaged one mating per day (mean of 1.0 ± 0.1), but some females mated up to eight times per day and some males up to six times per day. Reproductive success was estimated based both on observed numbers of matings in the field cage and on previous work relating fecundity and fertility to female mating status. Male and female flies did not differ in mean or variance in reproductive success, indicating that this is a polygamous mating system consisting of both polygyny and polyandry. We discuss the significance of this with regard to the framework of insect mating control and frequency proposed by others. We also discuss behaviors (such as movements, agonistic encounters, occurrences on fruit, and ovipositions) that do and do not show correlations with mating success in apple maggot flies.     

Correlates of male mating success in two natural populations of the damselfly lschnura graellsii (Odonata: Coenagrionidae)

Abstract.

• 1 Two natural populations of Ischnura graellsii were studied in north-west Spain by means of mark-release-recapture techniques. Recaptured males were a random sample of the original marked population with regard to date of marking. At O Rosal a greater proportion of young males than old males disappeared after marking; at Lourizán recaptured males were larger than unrecaptured ones.
• 2 The number of matings observed in both populations showed great daily variation. Most of the variation is accounted for by climatic variables. Most males (56–65%) and many females (41–45%) were never observed to mate.
• 3 Male LMS was highly correlated with lifespan in both populations. At O Rosal, male LMS was also positively correlated with body length, and mated males were larger than unmated males. This surprising result for a non-territorial species was due to the positive correlation between date of marking and size. There was a positive correlation between body size and mobility for males at O Rosal, but mobility was not correlated with male LMS.
• 4 As predicted by sexual selection theory, the standardized variance in male LMS was greater than in female LMS. Variation in mature lifespan explained 16% of variance in male LMS at Lourizán and 28% at O Rosal.

     

Reintroduction of the rare damselfly <Emphasis Type="Italic">Ischnura gemina</Emphasis> (Odonata: Coenagrionidae) into an urban California park

Habitat degradation led to local extinction of the San Francisco forktail damselfly (Ischnura gemina) in Glen Canyon Park, San Francisco, California. In this study, we reintroduced I. gemina into Glen Canyon after the damselfly’s habitat was restored. Upon release, we carried out a mark- release-recapture study to monitor the damselfly’s population dynamics. Our data were compared to two “baseline” studies on I. gemina, conducted in the park prior to the damselfly’s demise. Our recapture rates were significantly lower than the prior studies due to a large initial decline in marked individuals upon release. Despite a lower recapture rate, the reintroduction was initially successful since the damselflies reproduced throughout the summer and the following year. However, the population failed to persist during the second year when the habitat became degraded with excess vegetation. Future success is contingent on the continual management and upkeep of the habitat.     

Foraging behavior ofPachydiplax longipennis (Odonata: Libellulidae)

Food intake, prey availability, and prey capture behavior at feeding areas were quantified in the dragonflyPachydiplax longipennis by observing focal individuals on artificial perches, where they exhibited marked short-term site fidelity. Prey capture success was high and relatively constant, but the frequency and duration of feeding flights depended on the time of day and season (at least in part because of associated variation in temperature and other physical factors), study site, sex, density of other dragonflies, and prey density. Individuals rapidly responded temporally and spatially to changes in prey availability, particularly to localized prey concentrations.     

Population dynamics of Ischnura E. elegans (Vander Linden) (Insecta: Odonata) with special reference to morphological colour changes,female polymorphism,multiannual cycles and their influence on behaviour

Laboratory and field experiments on adult I. elegans provide correction techniques for the estimation of population parameters based only on capture-recapture data. Thus it is demonstrated that male and female longevities are identical and that their sex ratio is 0.5 (= Male fraction). Longevity, measured at the water, erroneously appears to differ between sexes, and sex ratio is also biased. This bias is a function of population density, which causes a different distribution of males and females, matures and immatures, andro- and heteromorphic females, and is regulated by aggressive, territorial and mating behaviour of individuals. The female maturation period exceeds that of the male. Female polymorphism is an adaptation to population density, high density favouring andromorphs. This polymorphism is determined by single allelic autosomal inheritance with a sex-linked expression. In crowded populations, visual interactions between individuals cause their juvenile hormone titer to rise. This shortens maturation time, the period of morphological colour changes, and life span. This mechanism counteracts crowding, and synchronises maturation and development of sexual behaviour. In the course of their life, individuals undergo a number of colour changes. The development of the colours after eclosion coincides with spermato- and oogenesis. The morphological colour change at sexual maturity is due to neutralisation of waste products of the protein metabolism. The colour changes at old age are partly due to dehydration.     

Morphological specializations of dorsal rim ommatidia in the compound eye of dragonflies and damselfies (Odonata)

We have examined the fine structure of dorsal rim ommatidia in the compound eye of the three odonate species Sympetrum striolatum, Aeshna cyanea and Ischnura elegans. These ommatidia exhibit several specializations: (1) the rhabdoms are very short, (2) there is no rhabdomeric twist, and (3) the rhabdoms contain only two, orthogonally-arranged microvillar orientations. The dorsal rim ommatidia of several other insect species are known to be anatomically specialized in a similar way and to be responsible for polarization vision. We suggest that the dorsal rim area of the odonate compound eye plays a similar role in polarization vision. Since the Odonata are a primitive group of insects, the use of polarized skylight for navigation may have developed early in insect phylogeny.