Establishment and organization of territories in the dragonfly Sympetrum rubicundulum (Odonata: Libellulidae)

Territory formation by males of the dragonfly Sympetrum rubicundulum was studied at a shallow temporary pond in Pennsylvania. Most males arrived at the pond between 1100 and 1200 hours and sought unoccupied sites in which to land, which they immediately began defending against conspecific males. Incoming males were never observed to challenge previous residents for possession of territories. Most conflicts between males occurred in the mid-afternoon and involved occupants of adjacent territories; residents experienced a clear ownership advantage in these conflicts. Escalated contests for possession of territory sites did not occur, perhaps because unoccupied sites were continually becoming available due to territory abandonment. Certain regions of the pond were consistently favoured by both sexes and most mating occurred in them: the spatial distributions of copulating pairs, ovipositing females and unpaired females were in close agreement with the spatial distribution of territorial males. High density sites were also the first sites occupied in the morning by incoming males. Although most of the pond and the surrounding land was thickly vegetated, territorial males and ovipositing females were both significantly clumped along the water's edge. The spatial distribution of males may have resulted from a balance of factors: peripheral sites were better than central ones for encountering incoming females, but areas far from the water's edge were unsuitable for female oviposition.     

Oviposition site selection and avoidance of additional mating by females of the dragonfly,Cordulia aenea amurensis Selys (Corduliidae)

Females of an odonate species in which oviposition sites overlap with mating sites may adopt one or more of the following strategies when they lay eggs except when they ‘trade’ mating for access to suitable oviposition sites or for services (guarding, etc.) provided by males: (1) ovipositing at hidden places; (2) ovipositing at a time when males are neither patrolling nor watching; (3) indicating non-receptivity by a behavioral display. The density of ovipositing females of the dragonfly, Cordulia aenea amurensisSelys which was studied between 1970 and 1983 at a pond (Hôrai-numa, Sapporo, Hokkaido) had a high negative correlation with the distance from ‘entrance’ (a part of shore at which the arrival of most adults seems to have occurred). On the other hand, oviposition was rarely observed at a sector being distant from entrance in spite of the inference that larval survivorship was probably high at this sector. Most females oviposited among emergent vegetation in which approach of males to them was difficult, and they scarcely traveled across the open water in search of oviposition sites. Therefore, most females of the population studied were considered to adopt the first strategy. The second and third strategy were not adopted by the population studied. Finally, the influences of some environmental factors and traits possessed by a species on the adoption of these tactics or on the execution of the ‘trades’ were discussed.     

Male perch selection and the mating system of the robber fly,Promachus albifacies (Diptera: Asilidae)

We studied the activity and spatial distribution of the robber fly,Promachus albifacies, in a desert grassland habitat in central New Mexico. Late in the season males spent most of the daytime on or near cholla and yucca plants that had dead stems or dead flower stalks at least 1 m high. Of the three hypotheses (thermoregulation, foraging, mate encounter site) considered as explanations for this distribution, the mate-encounter-site hypothesis was best supported. Plants used by females as oviposition sites were the focus of male activity. Males perched within or near these plants and attempted copulations with females detected nearby. Most matings were initiated at these locations. Seasonal changes in male and female activity also supported the mate-encounter-site hypothesis. Early in the season, females spent little time ovipositing, and predictably, males spent little time on or near these plants. Such a mating system may be described as resource defense polygyny, since males acted aggressively toward one another at oviposition sites even when females were not present. However, the short tenure of males at these sites is suggestive of scramble competition polygyny. We discuss possible reasons why this particular mating system has evolved.     

Pre-oviposition mate-guarding and mating behaviour of Argia vivida (Odonata: Coenagrionidae)

Abstract. 1. At Halcyon Hotsprings, British Columbia, Canada, male and female Argia vivida Hagen encountered to mate in two different ways.
2. In the morning (before 12.30 hours solar time), males basked at sunspots in the forest and darted out at passing females, attempting to take them in tandem (the first method of encounter).
3. If a male was successful, the pair engaged in a 31.3±4.8 min copulation followed by an hour of tandem flight before beginning oviposition.
4. As the day progressed, unmated males moved slowly toward the water and arrived at the water at about the same time as the earliest ovipositing pairs (1131±27.5 min solar time).
5. Males retained their grasp on their mates during oviposition (contact-guarding) but since some tandems separated during oviposition, non-tandem males at the water could capture recently released, gravid females (the second method of encounter).
6. The new pairs performed a brief copulation (10.2±3.38 min) and began ovipositing immediately thereafter.
7. Some females that avoided recapture attempted to oviposit unguarded.
8. We believe the long duration of morning copulations and period of tandem constitute a male strategy, which we call 'pre-oviposition guarding', to guard females until it is warm enough at the oviposition site for the females to begin ovipositing.
9. Separation of tandems during oviposition may be initiated by either member of the pair and we suggest that one benefit to a female of leaving a guarding mate is increased efficiency of oviposition when the intensity of male harassment is low.
10. The mating system of A. vivida thus comprises a series of complementary male and female mating behaviours.     

A reproductive tradeoff in an herbivorous lady beetle: egg resorption and female survival

A reproductive tradeoff between current egg production and subsequent survival in a lady beetle, Epilachna niponica, a specialist herbivore on a thistle, Cirsium kagamontanum, was investigated at the two study sites, A and F. Survival of reproductive females decreased consistently from early May until mid-June, but apparently increased thereafter. In contrast, males showed a consistent decrease in survival throughout the reproductive season, without any sign of recovery. Dissection of ovaries of sampled females revealed that egg resorption increased late in the reproductive season, coincident with increased female survival. Reproductive females stopped oviposition immediately after a large flood in 1979 at site F. Two weeks after the habitat perturbation, females resumed oviposition in response to a flush of new leaves on damaged plants. Female survival sharply increased during the nonoviposition period, and declined when egg-laying resumed. Approximately 40% of long-lived reproductive females at site F survived up to the following reproductive season in the next year. Also, some of these long-lived females were observed ovipositing in the following reproductive season. The long-lived reproductive females which had previously invested in reproduction survived equally well as newly emerged females which had not reproduced in summer. These results suggest that there is a reproductive tradeoff between current egg production and subsequent survival. Egg resorption may be an adaptive ovipositional response to habitat perturbation such as flooding, which considerably reduces offspring fitness due to absolute shortage of food. Also, increased female survival accompanied by egg resorption enhances the likelihood of the future oviposition in the second reproductive season, thereby increasing a female's lifetime reproductive success.     

Post-copulatory mate guarding by males of the demselfly Hetaerina vulnerata Selys (Odonata: Calopterygidae)

Males of the calopterygid damselfly Hetaerina vulnerata remain with their mates after copulating with them. The species exhibits two unusual features of post-copulatory mate guarding. First, a male will often leave his territory to accompany a female in tandem on a search for oviposition sites elsewhere. Second, a male will perch near his ovipositing female even though she completely submerges when egg-laying and cannot be captured and mated by another male while she is underwater. These activities carry two potential costs: (1) a male may miss other receptive females while guarding one mate and (2) he may lose his territory to an interloper while he is absent. These costs were low, however, because territorial males secured only one mating per 3.6 days on average. Moreover, 23 times out of 26, territorial males reclaimed their plots quickly after being away for 30–60 min. The gain from postcopulatory guarding came from being present to recapture a female should she fly up from the water after rejecting an oviposition site. There was a 40% chance that a female would leave one site to search for another during an oviposition bout. If the male were not present, his mate would be captured and mated by another individual (no female ever selected an oviposition site without being carried to it by a male). Her new partner would fertilize the remaining eggs in the female's clutch (if sperm precedence occurs in this species). The total number of eggs fertilized by a male will be affected by how well he prevents any one mate from copulating again before she lays her entire clutch and the total number of receptive females he captures. The variation in the degree of mate guarding by male odonates seems to be the evolutionary outcome of differences in fitness gains derived from these two competing activities in different ecological settings.     

The effects of feeding damage in ragweed Ambrosia artemisiifolia (Asteraceae) on populations of Zygogramma suturalis (Coleoptera,Chrysomelidae)

Summary Field sampling indicated that the number of eggs laid by a Zygogramma suturalis female within a sampling plot correlated inversely with the mean degree of ragweed damage. Feeding on extensively damaged ragweed in the laboratory caused a drop in oviposition intensity, and a considerable proportion of females completely stopped oviposition. Feeding on slightly damaged ragweed had no significant effect on oviposition intensity. Ovipositing females preferred to feed on the intact ragweed and lay their eggs close to it. The locomotory activity of ovipositing females was significantly higher on highly damaged ragweed whereas non-ovipositing (diapausing) females and males were behaviourally indifferent to the extent of ragweed damage. Under natural conditions, ovipositing females more frequently left damaged host plants for less damaged one. If the degree of ragweed damage is high over a large area, the insects that were unable to find undamaged plants for several days oviposited less and some females entered diapause. The adaptive effect of these reactions is a decrease of population density in advance, before it might drop as a result of starvation. These results are in agreement with the second model of insect reaction to the damage-induced changes in a host plant (Edwards and Wratten 1987).     

Reproductive behavior of the Japanese treefrog,Rhacophorus arboreus (Anura: Rhacophoridae)

Reproductive behavior of the foam-nesting treefrog,Rhacophorus arboreus, is described. Oviposition was made either by an amplectant pair (a female, and an amplectant male) alone or by an amplectant pair and other males (joiners). The snout-vent length of males and females was negatively correlated with the date of the first appearance in the pond. The period of staying in the pond in males was longer than that in females. Physical body contacts of other males, and encounter calls by ampletant males were frequently observed before oviposition with joiners. Snout-vent length of the female and an amplectant male were positively correlated. Encounter calls by amplectant males were likely to precede movement of females. There was no difference of snout-vent length between amplectant males and joiners. Females moved the hindlimbs more frequently than males during oviposition. Amplectant males made encounter cells more frequently in oviposition with joiners, than oviposition without joiners. The patterns of transitions between acts of females and amplectant males were similar between oviposition with and without joiners. Females more frequently responded to amplectant males than joiners. Both the duration of a bout of the movements of hindlimbs of females and the interval between the bouts were longer in oviposition without joiners than that with joiners. The number of the movements per bout in oviposition without joiners was smaller than that with joiners. Encounter calls by amplectant males during oviposition tended to precede the hindlimb movements of females.     

Mating or ovipositing? A crucial decision in the life history of the cabbage aphid parasitoid Diaeretiella rapae (M’Intosh)

1. The reproductive fitness of a parasitoid depends on its mating and ovipositing success. Virgin haplodiploid females can reproduce, but produce only males, and may diminish fitness by producing more male offspring than required. Therefore, females must decide on whether to mate or oviposit first. 2. This study was conducted to assess the mating versus ovipositing decision and its impact on the reproductive fitness of Diaeretiella rapae (Hymenoptera: Aphididae), an endoparasitoid of the cabbage aphid Brevicoryne brassicae (Hemiptera: Aphididae). 3. When newly emerged females were given a choice between mating and ovipositing, about 62% of D. rapae females preferred to mate before ovipositing. Those females who oviposited before mating parasitised only 10% of the available aphids. After mating, females superparasitised their hosts with fertilised eggs, which resulted in a highly female‐biased sex ratio in the offspring. 4. Mating success was very high (91%) in the presence of hosts (cabbage aphid nymphs) compared with that in the absence of aphids. However, mating success was not influenced by the quality (size) of the hosts present in the mating arena, despite a parasitoid preference for larger hosts during oviposition. The time between pairing and mating was also shorter in the presence of host aphids. The mean number of aphids parasitised and the parasitism rate were significantly greater after mating.     

Hold on: Females modulate sperm depletion from storage sites in the fly Drosophila melanogaster

Among many species of insects, females gain fitness benefits by producing numerous offspring. Yet actions related to producing numerous offspring such as mating with multiple males, producing oocytes and placing offspring in sub-optimal environments incur costs. Females can decrease the magnitude of these costs by retaining gametes when suitable oviposition sites are absent. We used the pomace fly, Drosophila melanogaster, to explore how the availability of fresh feeding/oviposition medium influenced female fitness via changes in offspring survivorship and the modulation of gamete release. Availability of fresh medium affected the absolute number and temporal production of offspring. This outcome was attributable to both decreased larval survival under crowded conditions and to female modulation of gamete release. Direct examination of the number of sperm retained among the different female storage organs revealed that females ‘hold on’ to sperm, retaining more sperm in storage, disproportionately within the spermathecae, when exposed infrequently to fresh medium. Despite this retention, females with lower rates of storage depletion exhibited decreased sperm use efficiency shortly after mating. This study provides direct evidence that females influence the rate of sperm depletion from specific storage sites in a way that can affect both female and male fitness. The possible adaptive significance of selective gamete utilization by female Drosophila includes lowering costs associated with frequent remating and larval overcrowding when oviposition sites are limiting, as well as potentially influencing paternity when females store sperm from multiple males.     

Effects of meadow suitability on female behaviour in the alpine butterfly Parnassius smintheus

Abstract  1. Many butterfly populations persist in networks of naturally fragmented habitat patches. Movement and reproductive decisions made by adult females are critical to the persistence of these populations because colonisation of extinct habitat patches in the network requires emigration of fecund adult females from their natal meadow and their subsequent establishment in the extinct patch.
2. Movement and oviposition behaviours of mated Parnassius smintheus females released in suitable meadows (a good- and a poor-quality meadow) and an unsuitable meadow were compared, to determine whether adult females consider meadow suitability for their offspring despite frequent oviposition events off the larval host plant.
3. Bootstrap and correlated random walk analyses of female step lengths and turn angles demonstrated that females flew more randomly in the unsuitable meadow than in the suitable meadows. Although females tended to turn the sharpest angle between landing sites in the good-quality meadow, and fly the smallest distance between landing sites and displace the smallest distance from the release site in the suitable meadows, no significant differences were detected in turn angle, step length, and dispersal rates between suitable and unsuitable meadows.
4. Results from female flight observations and a caged oviposition study suggest that females lay significantly more eggs in suitable habitat than in unsuitable habitat despite not ovipositing on the host plant, and support the above findings.
5. Movement and oviposition behaviours of adult female P. smintheus promote their retention within meadows that can support their offspring.     

Alternative mate-finding tactics in a non-territorial damselfly (Odonata: Coenagrionidae)

Males of the non-territorial damselfly Enallagma hageni have two alternative tactics for finding mates: (1) they search the banks of the pond for unmated females (searching tactic), or (2) wait at oviposition sites for females that resurface prematurely from underwater oviposition (waiting tactic). Although the searching tactic yielded more fertilizations than the waiting tactic, for time invested, the waiting tactic became increasingly successful later in the reproductive season due to changes in female oviposition behaviour. The two tactics can be maintained in the population because males can mate by the waiting tactic during the afternoon when few females are available to searchers. Among males visiting the breeding site an equal number of times, males mating by a mixture of tactics were as successful as males mating only by the main tactic. Because marked males were found to use both tactics, these behaviours are interpreted as evidence of behavioural plasticity within individuals, representing one conditional evolutionary strategy.     

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.     

Avoidance of egg parasitism through submerged oviposition by tandem pairs in the water strider, Aquarius paludum insularis (Heteroptera: Gerridae)

Abstract.  1. Females of the water strider Aquarius paludum insularis (Motschulsky) (Heteroptera: Gerridae) carry males on their backs and oviposit under water after copulation. This study focuses on the benefit  A. paludum insularis receives by ovipositing in tandem.
2. Males guarded females in tandem through to the end of oviposition in 85% of copulations. Females in tandem dived deeper than single females, and the density of A. paludum insularis eggs increased with water depth. The proportion of eggs parasitized by a scelionid wasp, Tiphodytes gerriphagus Marchal (Hymenoptera: Scelionidae) decreased with increasing water depth.
3. These results suggest that during oviposition guarding by males is beneficial for females, because it enables pairs to dive and lay eggs deeper and in oviposition sites where the risk of egg parasitism is lower.     

Brood conspicuousness and clutch viability in male‐caring assassin bugs (Rhinocoris tristis)

Abstract 1. Conspicuousness to mates can bring benefits to both males (increased mating success) and females (reduced search costs), but also brings costs (e.g. increased predation and parasitism). Assassin bugs, Rhinocoris tristis, lay egg clutches either on exposed stems or hidden under leaves. Males guard eggs against parasitoids. Guarding males are attractive to females who add subsequent clutches to the brood. This is an excellent opportunity to study the effects of conspicuousness on the fitness of males and females. 2. Using viable eggs in a multi‐clutch brood as a correlate of fitness, the present study examined whether laying eggs on stems affected (1) female fitness, through exposure to parasitism and cannibalism, and (2) male fitness, through attracting further females. 3. Stem broods were more parasitised. However, males on stems accumulated more mates and more eggs, a net benefit even accounting for parasitism. The eggs gained from being on a stem were cannibalised. By contrast, higher mortality on stems suggests that females should gain by ovipositing on leaves. To the extent that egg viability represents fitness, male and female interests may therefore differ. This suggests a potential for sexual conflict that may affect other species with male care. 4. Despite higher costs, females actually initiated more broods, and subsequently added bigger clutches to broods, on stems than under leaves. This suggests either that viable eggs do not reflect fitness, or that females laid in unfavourable locations. The key is now to address lifetime fitness, since unmeasured factors may affect offspring viability post‐hatching, and to investigate who controls the location of oviposition in R. tristis.     

Oviposition habitat selection by the mosquito Culiseta longiareolata in response to risk of predation and conspecific larval density

Abstract. 1. Most female Culiseta longiareolata (Diptera: Culicidae) avoid ovipositing in pools that contain the predatory backswimmer Notonecta maculata . Such oviposition habitat selection has been suggested to reflect a trade-off between the risk of predation on larvae and potential density-dependent fitness costs. This putative trade-off was examined. In particular, evidence was sought in support of direct female response to local heterogeneity in habitat quality.
2. Three habitat types were established using artificial outdoor pools: predator pools, and non-predator pools with either low or high densities of Culiseta larvae. During each experimental night, females were offered one of the three possible pair-wise treatment combinations.
3. The majority (≈88%) of females oviposited in low-density pools rather than in the predator- or high-density pools. Furthermore, a substantially higher proportion of females oviposited in predator pools when faced with the high-density alternative, however this was due largely to fewer females ovipositing in high- vs low-density pools.
4. Females of a second mosquito species ( Culex laticinctus ), the larvae of which are at a lower risk of predation, were predicted to exhibit weaker aversion to N. maculata ; this prediction was supported only weakly.
5. Oviposition habitat selection by female C. longiareolata does not appear to involve a behavioural response that is based on individual assessment of local heterogeneity in relative pool quality, at least not at the spatial scale examined here; alternative explanations are discussed.     

Habitat availability mediates chironomid density-dependent oviposition

Knowledge of density-dependent processes and how they are mediated by environmental factors is critically important for understanding population and community ecology of insects, as well as for mitigating harmful insect-borne diseases. Here, we tested whether the oviposition of chironomids (Diptera: Chironomidae; non-biting midges), known to carry the Cholera pathogen Vibrio cholerae, is density dependent and if it is mediated by habitat availability. We used two multiple choice experiments in habitat-limited and habitat-unlimited environments and performed isodar analysis on counts of egg batches after controlling the polarization of light reflected from the habitats, which is known to affect their attractiveness to ovipositing chironomids. We found that, when habitats are limited, egg batch isodars indicate that chironomid selection is density dependent. Although a greater number of individuals selected to oviposit in highly polarized sites, oviposition was also common in sites with low polarization. When habitats are unlimited, chironomid selection is either weakly density dependent, or completely density independent. Chironomids oviposit to a very large extent in sites with high level of polarization, oviposit to a small extent in sites with medium level of polarization, and almost completely disregard unpolarized sites. We suggest that ovipositing females consider the availability of habitats in their surroundings when they choose an oviposition site. When high quality habitats are scarce, more females opt to breed in low quality sites. These findings may be used to limit the spread of Cholera by controlling the habitats available for chironomid oviposition.     

Spatial distribution of mate-searching males in the damselfly,Cercion c. calamorum (Odonata: Zygoptera)

Both sexes of the coenagrionid damselflyCercion c. calamorum meet at, or near, ponds for oviposition. Spatial distribution of mate-searching males at a study pond was established with the following 2 simple and independent rules: (1) males don't go far from the roosting sites of the previous night; (2) once males reach one of the oviposition sites, the length of their stay is related to site quality. The first rule may correspond to the decrease in the number of receptive females at greater distances from the shore, and the second rule may relate to the higher predictability of female arrival at better oviposition sites. Contribution from the Laboratory of Animal Ecology, Kyoto University, No. 543.     

Tests for sex differences in fitness-linked traits in the spiderAgelenopsis aperta (Araneae: Agelenidae)

The idea that traits linked to individual fitness may differ between males and females was tested in the desert funnel-web spider,Agelenopsis aperta. The study entailed comparison of juvenile male and female behavior with respect to three traits previously shown to be linked to female body mass and ultimately to individual female fitness: habitat discrimination, territorial behavior, and agonistic behavior. As juveniles, male and female spiders behave similarly: they utilize the same habitat cues in locating web sites, maintain similar territory sizes, and exhibit the same behavior patterns in territorial disputes. Like females, males that obtain the highest-quality web sites achieve a greater body mass and are more likely to survive to maturity.