Stage-dependent predation on competitors: consequences for the outcome of a mosquito invasion

1. Predator-mediated coexistence occurs when predation allows competitors to coexist, due to preferential consumption of a superior competitor relative to an inferior competitor. Differences between the native treehole mosquito ( Aedes triseriatus ) and the co-occurring Asian tiger mosquito ( Aedes albopictus ) in anti-predatory larval behaviours account, in part, for the greater vulnerability of this invasive species to native predatory midge ( Corethrella appendiculata ). We test the hypothesis that stage-dependent differences in the sizes of A. albopictus and A. triseriatus larvae, relative to the size-limited C. appendiculata , contribute to differential consumption and the likelihood of predator-mediated coexistence of these competitors.
2. In all instars, larvae of A. triseriatus were larger than A. albopictus of the same stage. Third and fourth instar C. appendiculata selectively consumed late-stage A. albopictus in preference to same-stage A. triseriatus . Small, early-stage prey larvae did not differ in vulnerability to predation, but large, late-stage larvae differed significantly in vulnerability to predation, probably owing to size-limited predation by fourth instar C. appendiculata. This effect was less pronounced for third instar C. appendiculata .
3. Prey size, in conjunction with anti-predatory behavioural responses, alters the probability of predator-mediated coexistence. A stage-structured predation model showed that equally vulnerable early stages reduce the range of environmental conditions (productivities) in which predator-mediated coexistence is possible, increasing the likelihood of both competitive exclusion of the resident species or failure of the invasive to establish. These results underscore the importance of stage-dependent interspecific differences in predator–prey interactions for determining how predators may affect community composition.     

Does differential predation permit invasive and native mosquito larvae to coexist in Florida?

Abstract.  1. The hypothesis that selective predation on larvae of the invasive Aedes albopictus (Skuse) could account for its stable coexistence with the native mosquito species and inferior competitor Ochlerotatus triseriatus (Say) in Florida treeholes and container systems was tested experimentally.
2. Functional responses of the two dipteran predators Toxorhynchites rutilus (Coquillett) and Corethrella appendiculata (Grabham) were evaluated separately for A. albopictus and O. triseriatus prey. Both predators exhibited type II functional responses and consistently consumed more of the invasive species. Handling time of T. rutilus feeding upon O. triseriatus was significantly longer than when preying upon the invasive species.
3. When either predator species was offered varying ratios of the two prey species, A. albopictus was consumed preferentially. The absence of a prey ratio effect on preference indicated that switching probably does not occur.
4. The higher maximum feeding rate upon, and preference for, A. albopictus suggests that differential predation may foster coexistence of the invasive and native mosquito prey species in Florida.     

Differential Behavioral Responses to Water-Borne Cues to Predation in Two Container-Dwelling Mosquitoes

Larvae of the mosquito Toxorhynchites rutilus (Coquillett) prey upon other container-dwelling insects, including larvae of Aedes albopictus (Skuse), which is native to Asia but was introduced into the United States, and on the native tree hole mosquito Ochlerotatus triseriatus (Say). Previous work has established that O. triseriatus adopts low-risk behaviors in the presence of predation risk from T. rutilus. It is unknown whether introduced A. albopictus show a similar response to this predator. Behavior of fourth instars of A. albopictus or O. triseriatus was recorded in water that had held either A. albopictus or O. triseriatus larvae alone (control) and in water that had held T. rutilus larvae feeding on either A. albopictus or O. triseriatus (predation). Activity and position of larvae were recorded in 30-min instantaneous scan censuses. In response to water-borne cues to predation, O. triseriatus adopted low-risk behaviors (more resting, less feeding and movement), but A. albopictus did not change its behavior. We also tested the species specificity of the cues by recording the behavior of A. albopictus in water prepared using O. triseriatus and vice versa. O. triseriatus adopted low-risk behaviors even in predation water prepared by feeding T. rutilus with A. albopictus, but A. albopictus did not alter its behavior significantly between predation and control treatments prepared using O. triseriatus. Thus, A. albopictus does not seem to respond behaviorally to cues produced by this predator and may be more vulnerable to predation than is O. triseriatus.     

Competitive Outcomes of Aquatic Container Diptera Depend on Predation and Resource Levels

Resources and predation are both known to be important in structuring communities; however the strength of one factor may be affected by the intensity of the other. This study used a fully crossed factorial experiment in laboratory microcosms to examine the ability of a predator, Corethrella appendiculata (Grabham), and basal resources (leaf litter) to differentially affect two competing species of mosquito prey. Increased resources resulted in shorter developmental time and increased survivorship, mass, and population performance for both prey species, except when predation levels were high. Increased levels of predation and resources reduced the negative competitive effects of Aedes albopictus (Skuse) on Ochlerotatus triseriatus (Say). At low levels of resources and predation, the superior competitor, A. albopictus had the higher survivorship, and at high levels of resources and predation, the inferior competitor's survival was greater. Predators in high-resource treatments emerged larger than those in low resources, suggesting the occurrence of a bottom-up cascade or alternative feeding method. This study suggests that survival and coexistence of the two prey species may depend on the interaction of resources and predation, in that high levels of predation are important for the coexistence of both species.     

Nature of Predation Risk Cues in Container Systems: Mosquito Responses to Solid Residues From Predation

In aquatic systems, prey animals associate predation risk with cues that originate either from the predator or from injured conspecifics. Sources and benefits of these cues have received considerable attention in river, lake, and pond ecosystems but are less well understood in small container ecosystems that can hold less than a liter of water. Mosquitoes Aedes triseriatus (Say) and Aedes albopictus (Skuse) encounter predatory Corethrella appendiculata (Grabham) and Toxorhynchites rutilus (Coquillett) in small containers and show antipredatory behavioral responses. We investigated the sources of the predation cues to which these prey larvae respond. We tested whether Ae. albopictus larvae show behavioral responses to cues emanating from the predator or from damage to prey caused by the act of predation. We also tested whether Ae. triseriatus respond to cues present in fluid or solid residues from predator activity. Ae. albopictus showed behavioral modifications only in response to waterborne cues from a feeding predator and not to cues from a starving predator, indicating that Ae. albopictus respond to cues created by the act of predation, which could include substances derived from damaged prey or substances in predator feces. Ae. triseriatus showed behavioral responses to solid residues from predation but not to fluid without those solids, indicating that the cues to which they respond originate in predator feces or uneaten prey body parts. Our results suggest that cues in this system may be primarily chemicals that are detected upon contact with solid residues that are products of the feeding processes of these predators.     

Threat-Sensitive Behavioral Responses to Concentrations of Water-Borne Cues from Predation

Aquatic organisms often detect predators via water-borne chemical cues, and respond by showing reduced activity. Prey responses may be correlated with the concentration of predation cues, which would result in graded antipredator behavioral responses that adjust potentially costly behavioral changes to levels that are commensurate with the risk of predation. Larvae of the predatory mosquito Toxorhynchites rutilus prey upon other container-dwelling insects, including larvae of the mosquito Ochlerotatus triseriatus. Previous work has established that O. triseriatus reduce movement, foraging, and time below the surface, and increase the frequency of resting at the surface, in the presence of water-borne cues from predation by T. rutilus. We tested whether these responses by O. triseriatus are threat sensitive by recording behavior of fourth instar larvae in two runs of an experiment in which we created a series of concentrations (100, 10, 1, 0.1, and 0.01% and 100, 70, 40, 20, and 10%) of water that had held either O. triseriatus larvae alone (control) or a T. rutilus larva feeding on O. triseriatus (predation). We also tested whether associated effects on time spent feeding are threat sensitive by determining whether frequencies of filtering or browsing are also related to concentration of cues. The frequencies of resting and surface declined, whereas frequency of filtering (but not browsing) increased more rapidly with a decrease in concentration of predation cues compared with control cues. Thus, O. triseriatus shows a threat sensitive behavioral response to water-borne cues from this predator, adjusting its degree of behavioral response to the apparent risk of predation.     

Predatory interactions between a cyclopoid copepod and three sibling rotifer species

SUMMARY 1. Cyclopoid copepod predation on rotifers affects the dynamics and structure of zooplankton communities. We address the differential vulnerability of three sympatric rotifer sibling species belonging to the Brachionus plicatilis species complex. These co-occur with their cyclopoid predator, Diacyclops bicuspidatus odessanus .
2. Using video recording and tracking, we analysed the steps in predation including attack distance, attack angle, and rotifer species swimming in the presence and absence of the predator. Our results show the greater vulnerability of B. rotundiformis (the smallest species) to D. b. odessanus predation, which is associated with a high percentage of attacks after contact. Brachionus plicatilis (the biggest species) is the less vulnerable prey, with low percentage of attacks after contact and captures after attacks. Branchionus ibericus , the intermediate sized species, had also intermediate vulnerability.
3. The differential vulnerability provides insight into the coexistence and seasonal succession of these competing rotifer species. Our results show that the competitive superiority of B. rotundiformis may be balanced by its greater vulnerability to copepod predation.     

Dropping behaviour of larvae of aphidophagous ladybirds and its effects on incidence of intraguild predation: interactions between the intraguild prey, Adalia bipunctata (L.) and Coccinella septempunctata (L.), and the intraguild predator, Harmonia axyridis Pallas

Abstract.  1. Two experiments were performed in the laboratory to assess the behaviour of dropping from a host plant as a defence against intraguild predation in aphidophagous ladybird larvae.
2. In the first experiment, encounters were observed on bean plants between fourth instars of the intraguild predator species, Harmonia axyridis , and first instars of two other ladybird species, Adalia bipunctata (L.) and Coccinella septempunctata (L.). The percentages of first instars of the latter two species that dropped from the plant in response to attack differed dramatically, with 47.5% of C. septempunctata first instars dropping vs. 0% of A. bipunctata .
3. In the second experiment, first instars of A. bipunctata or C. septempunctata and a fourth instar of H. axyridis were allowed to forage together on bean plants for 3 h. During this time, 44.3% of C. septempunctata larvae dropped from the plant, but less than 2% of A. bipunctata larvae did so. In contrast, 95.0% of A. bipunctata larvae fell victim to intraguild predation by H. axyridis vs. only 54.5% of C. septempunctata larvae.
4. The significance of dropping behaviour of ladybird larvae as a defence against intraguild predation, and the relationship of dropping behaviour to species-specific habitat affinity of ladybirds, is discussed.     

Larval rearing conditions affect kin-mediated cannibalism in a treehole mosquito

Cannibalistic behavior among Ochlerotatus triseriatus larvae was studied to determine whether cannibals are able to alter their attack behavior based on their relatedness to newly hatched conspecific prey larvae. Fourth instar larvae, reared in one of four different initial densities, were placed with newly emerged first instars and, after 48 h, the number of first instar larvae remaining was recorded. Our data suggest a Type III functional response of non-kin fourth instar larvae to first instar prey density. Several significant effects emerged from our analysis model, namely that the number of first instar prey available, the relationship of the first instar larvae with the cannibals, and the density at which the fourth instar cannibals were reared all affected the number of first instar larvae consumed.     

Intraguild predation by the generalist predator Orius majusculus on the parasitoid Encarsia formosa

Intraguild predation of Orius majusculus (Reuter) (Heteroptera: Anthocoridae) on Encarsia formosa (Gahan) (Hymenoptera: Aphelinidae), both natural enemies of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), was studied under laboratory conditions. The experiments quantified prey consumption by 5th instar nymphs and adults of O. majusculus offered unparasitised 3rd, early 4th or 4th instar B. tabaci nymphs or parasitised nymphs containing 2nd or 3rd larval instar or pupal parasitoids. In addition, prey preference of the two stages of O. majusculus for parasitised or unparasitised whitefly nymphs was studied using nine different prey combinations. Both predator stages readily preyed upon on both unparasitised and parasitised B. tabaci. In no-choice experiments, predation on 3rd instar E. formosa by adult predators was the highest, while predator nymphs preyed most on unparasitised 3rd instar B. tabaci and 2nd instar parasitoids. Predation of predator stages was lowest on 4th instar B. tabaci and E. formosa pupae. In all prey combinations, both stages of O. majusculus showed a significant preference for parasitised over unparasitised whitefly nymphs except for the combination of 5th instars of O. majusculus with early 4th instar whiteflies and E. formosa pupae. The results indicate that intraguild interactions between O. majusculus and E. formosa may have negative effects on biological control of B. tabaci.     

Trait‐mediated effects of predation across life‐history stages in container mosquitoes

1. It was determined if the predatory midge Corethrella appendiculata Grabham imposes a fitness cost in a native mosquito, Ochlerotatus triseriatus Say, and an invasive mosquito, Aedes albopictus Skuse. The hypothesis that decreased activity of immature prey in the presence of predator cues is associated with life history costs through all life cycle stages was tested. 2. In experiment 1, individual larvae of O. triseriatus or A. albopictus were raised in the presence or absence of predation cues at two resource levels. Prey were video recorded to detect behavioural responses and to measure development time, size at emergence, and adult longevity. In experiment 2, prey populations were reared in similar environments and the frequency of predator cue additions was varied. 3. Only O. triseriatus reduced its activity in the presence of predation cues. Predation cues were associated with longer immature development times and shorter adult life spans in O. triseriatus, whereas in A. albopictus, the cues were associated with a larger size of emerging adults. 4. In the present study, it was found that behavioural modifications during the larval stage can affect mosquitoes through multiple stages of their complex life cycle. The species‐specific behavioural differences are probably attributable to the longer evolutionary history O. triseriatus has with predators, relative to the invasive A. albopictus.     

Interactions with native mosquito larvae regulate the production of Aedes albopictus from bromeliads in Florida

Abstract. 1. Immatures of the invasive container mosquito Aedes albopictus occur in water-holding tanks and axils of ornamental bromeliads in Florida, where this species established and became abundant in the late 1980s and early 1990s.
2. The numbers of A. albopictus in bromeliads in gardens vary geographically in Florida, being significantly higher in northern sites where two species of Wyeomyia mosquitoes, native specialists of this microhabitat, are absent.
3. Causes of the negative relationship between abundances of A. albopictus and Wyeomyia spp. were investigated experimentally using Billbergia pyramidalis , an introduced bromeliad popular in Florida gardens.
4. Egg laying by A. albopictus in B. pyramidalis confined in a large outdoor cage was unaffected by the presence or absence of Wyeomyia spp. fourth instars, indicating that immatures of the native bromeliad mosquito species do not deter oviposition by the invasive species in this microhabitat.
5. Growth and survivorship of A. albopictus first instars in tanks of B. pyramidalis were negatively affected by the presence of fourth instar, but not first instar, Wyeomyia spp. larvae at natural densities. Stimulative effects of leaf litter on A. albopictus growth and survivorship in this microhabitat were independent of the presence or absence of Wyeomyia spp. immatures.
6. These results demonstrate that interspecific larval interactions regulate the production and explain the geographic patterns in abundance of A. albopictus from ornamental bromeliads in Florida.     

The significance of ratios of detritus types and micro-organism productivity to competitive interactions between aquatic insect detritivores

Investigations of competitive interactions emphasize non-detrital resources, even though detritus is a major component of most food webs. Studies of competing species focus usually on single resource types, although consumers in nature are likely to encounter mixtures of resource types that may affect whether competition results in exclusion or coexistence. The invasive mosquito Aedes albopictus is capable of excluding the native mosquito Ochlerotatus triseriatus in competition for single detritus types in laboratory and field microcosms. In this study, we used nine ratios of two detritus types (animal and leaf) common in natural containers to test whether detritus ratios affect the outcome of competition. Under intraspecific and interspecific competition, A. albopictus attained higher survival and estimated population growth rate than did O. triseriatus. Unlike past studies, both species had positive growth and high adult survival, with little evidence of competitive effects, under one resource ratio (10:1 ratio of leaf : animal detritus) regardless of mosquito densities, suggesting potential coexistence. Path analysis showed that densities of larvae had negative effects on population growth for O. triseriatus but not for A. albopictus, indicating competitive superiority of A. albopictus. Population growth of both species was affected strongly by the direct paths from animal (positive) and leaf (negative) detritus, and the indirect effect of leaf detritus via bacterial production (positive). Field sampling established that detritus entered real tree holes in ratios similar to those in our experiment, suggesting that natural variation in detritus ratios may influence local coexistence of these species. Seasonal variation in ratios of plant and animal detritus indicated that temporal as well as spatial variation in inputs may be important for potential coexistence.     

Dynamics of handling time and functional response by larvae of Chrysomya albiceps (Dipt., Calliphoridae) on different prey species

Abstract:  One way to understand the behavioural patterns exhibited by a predator in response to prey density is to evaluate its functional response. Such evaluation yields information about basic mechanisms of prey–predator dynamics, and is an essential component of prey–predator models. In this paper we analysed experimentally the functional response and the handling time spent by Chrysomya albiceps on different prey species and larval instars of blowflies. The type II functional response was observed when second instar larvae of Chrysomya megacephala and Chrysomya macellaria were consumed. The handling time spent by the predator was significantly different between instars and species. The implications of the functional response and handling time for the interaction dynamics of Brazilian Chrysomyinae species are discussed.     

南方小花蝽对西花蓟马和蚕豆蚜的捕食作用

南方小花蝽Orius similis是多种小型害虫的重要天敌昆虫,为了掌握其控制潜能,本文研究了南方小花蝽对西花蓟马Frankliniella occidentalis和蚕豆蚜Aphis craccivora的捕食作用。研究结果表明南方小花蝽3～5龄若虫和雌成虫对西花蓟马和蚕豆蚜的功能反应均符合HollingⅡ型方程,南方小花蝽3～5龄若虫和雌成虫对西花蓟马2龄若虫的瞬时攻击率均高于蚕豆蚜。南方小花蝽5龄若虫对蚕豆蚜的控制能力比雌成虫强,而对西花蓟马的控制能力比雌成虫差。南方小花蝽5龄若虫对西花蓟马2龄若虫和蚕豆蚜的捕食率（E）随着捕食者自身的密度（P）的增加而下降,其干扰反应方程分别为E=0.412P-1.623和E=0.416P-1.639。南方小花蝽5龄若虫对西花蓟马2龄若虫和蚕豆蚜有明显的选择性,5龄若虫喜欢取食西花蓟马2龄若虫,但前期取食的猎物对其选择性有明显的影响,更喜欢选择前期取食过的猎物。     

Food selectivity and diel vertical distribution of Chaoborus edulis (Diptera, Chaoboridae) in Lake Malawi

1. Diel diet and vertical distribution patterns of the larval instars of Chaoborus edulis were studied in deep water near the central part of Lake Malawi, Africa.
2. First instar larvae contained very little food in their crops and probably depended on reserves from the egg. Second, third and fourth instars fed on zooplankton and were size-selective in their feeding. The mean size of prey eaten by the three instars was significantly different from each other, with larger instars feeding on larger prey. Smallest available prey was selected against and the upper size of prey was probably constrained by larval gape. Nauplii were not found in any of several thousand larvae examined. Phytoplankton did not form a significant part of the diet.
3. There was a progressive and related increase in diel periodicity in feeding and vertical migrations of successive instar stages. Fourth instars migrated particularly large distances. Such migrations removed them from their zooplankton food supply but avoided predators. A refuge from predators is probably found in or near the permanent zero oxygen boundary, at depths greater than 200 m.     

叉角厉蝽对斜纹夜蛾不同龄期幼虫的选择捕食作用

应用二次回归通用旋转组合设计探讨了叉角厉蝽与斜纹夜蛾低龄幼虫,中龄幼虫和高龄幼虫共存系统中,天敌对猎物不同年龄等级的选择捕食作用,建立了3个年龄等级的幼虫被捕食量模型。根据被捕食量模型可计算出斜纹夜蛾3个年龄等级不同密度组合下,天敌对猎物的选择捕食比率,结果表明,在3个年龄等级相同密度的组合下,叉角厉蝽倾向于捕食个体大的中高龄幼虫。     

Where to stay by night and day: Size-specific and seasonal differences in horizontal and vertical distribution of Chaoborus flavicans larvae

1. Data on the distributions of pelagic and benthic Chaoborus flavicans larvae were gathered in 1994 and tested for their agreement with the predator avoidance hypotheses. The development of all Chaoborus life stages, as well as the horizontal and vertical distribution in the four larval instars, was followed from May until October. We expected the largest larvae to dwell deeper by day, thus avoiding predation by visually foraging fish.
2. In agreement with this prediction body size increased with daytime depth, and this was true both between and within instars. The migration amplitude consequently increased with larval instar.
3. There was also evidence for horizontal migration, mainly in the third but also in the fourth instar.
4. Along a horizontal transect with increasing depth, locations with many benthic larvae had fewer pelagic larvae. Oxygen concentration was a good predictor of maximum benthic larval depth for most of the season but failed to predict their distribution in autumn.     

Effects of prey-size and predator-instar on the predation of Daphnia by Notonecta

Abstract. 1. Attack rates and handling times are measured by a series of separate functional response experiments for each instar of Notonecta glauca attacking four size classes of Daphnia magna as prey. The resulting attack rate and handling time surfaces are complex, with maximum attack rates for small predators attacking small prey, and large predators attacking large prey. Adult Notonecta have lower attack rates than the two previous juvenile instars (4 and 5).
2. The literature on attack rates and handling times in other predator—prey interactions that involve a series of different predator and prey size or age classes is reviewed in the context of the Notonecta-Daphnia results. The data suggest that small predator instars will usually compete with large instars for food, unless there is spatial or temporal separation between them.
3. Complex attack rate and handling time surfaces are to be expected wherever a wide range of prey and predator sizes is involved.
4. Size related changes in attack rates and handling times can introduce very complex dynamics into predator-prey interactions.     

Studies on predation of the mosquito Culex fatigans by Rana tigrina tadpoles

Satiated predation, predation rate and prey preference of different weight groups of Rana tigrina (Daud) tadpoles on different larval and pupal stages of Culex fatigans were studied. Irrespective of the prey and predator size, the satiation time remained more or less equal. There exists a mass-dependent predation: Calculated predation rates or predatory constants (Kpr) showed that I instar prey was preyed upon at about equal rate, while other instars and pupa showed an increasing trend with increasing body weight of the predator. The prey preference assessed using the Kpr, revealed that prey size is an important parameter in predation. The R. tigrina tadpole is a more efficient pupal predator than other mosquito predators.