Search orientation of Musca domestica in patches of sucrose drops

ABSTRACT. The searching tactics of the housefly, Musca dormestica L. (Diptera: Muscidae), have been delineated from digitized pathways of flies walking in patches of sucrose drops arranged in linear (ROW) and hexagonal (HEX) arrays. The areas covered by flies in ROW and HEX patches are distinctly different, but flies seem not to employ different tactics for the two types of resource arrays. The number of drops located, if at least one drop is found, does not differ between ROW and HEX. Most quantitative measures of local search remain constant after the first interdrop interval, although feeding time decreases as flies sample successive drops. Local search intensifies after each drop is ingested, with locomotory rate decreasing and turning rate increasing, followed by decay of both measures toward ranging levels. Searching can be characterized by two movement tendencies resulting from specific, definable, locomotory functions: a forward-moving tendency is expressed by the fly as it leaves a resource in approximately the same direction as it arrives; and local search is characterized by looping, rather than straight walking, with a variable turning rate that generates a rough ‘zigzag’ superimposed on looping. The two movement tendencies, combined, allow flies to locate resources in a linear arrangement, because of the forward-moving tendency, and to locate resources not arranged in a linear array because of the ‘noisy’ loop. M. domestica does not appear to retain and use information gained from one patch of drops in another, so the search tactic of the fly seems therefore to be a compromise between straight movement and circular movement that may be adaptive for an environment subject to frequent changes in the spatial distribution of resources. Giving-up-time, the period between ingesting the last drop and leaving the patch, is a function of the rate of change in the transition from local search to ranging, which is constant in our experiments. If a fly does not encounter another drop while ranging, during which it walks relatively straight, the fly moves out of and away from the patch.     

Host frass as arrestant chemicals in locating host Mythimna separata by the tachinid fly Exorista japonica

We investigated the response of the tachinid fly, Exorista japonica (Townsend), to host frass or its extracts in order to clarify the host location mechanisms of female flies in a potential host habitat. Host searching time in a patch and the number of patch visits were analyzed by using a frass-containing patch which was excreted by host larvae, Mythimna separata (Walker) (Lepidoptera: Noctuidae), and patches to which host frass extracts were applied. E. japonica females were arrested in response to the host-frass-containing patch after contacting the frass with their front tarsi, thereby spending most of the time to search the patch and to revisit the host-frass patch. While host-searching time in the patch by the females was longest at their first visit of a patch with host frass, searching time decreased with successive visits. The female flies also exhibited area-restricted searching with methanol extracts of the host frass. Area-restricted searching activity increased with the concentration of host-frass extract, i.e., total searching time in the patch and the number of patch visits varied in a dose-dependent manner. E. japonica females likely employ chemicals in host frass as arrestants in host location.     

Tracking dispersal across a patchy landscape reveals a dynamic interaction between genotype and habitat structure

Theoretical and empirical studies often show that within populations, individuals vary in their propensity to disperse. We aspired to understand how this behavioural variation is impacted by the distribution and pattern of food patches across a landscape. In a series of experiments we examined how inter-patch distance and the distribution of food patches influenced dispersal in wild-type strains of Drosophila melanogaster with natural allelic variants of the foraging (for) gene known to influence dispersal in this species. The ‘rover' strain was homozygous for the for^R allele (more dispersive) whereas the ‘sitter' strain was homozygous for for^s (less dispersive). We also assessed an outbred population of flies with an unknown dispersal propensity. Dispersal was assayed in a multi-patch lab arena (25 cells, 5 × 5 array). In the inter-patch distance trials, landscapes of two different sizes (small versus large) were used, both with food in all 25 cells. Dispersal was reduced in the large landscape relative to the small landscape for all three fly strains. Sitter dispersal was lowest relative to both rovers and the outbred flies, whose dispersal tendencies were similar. In the patch distribution trials, flies were assayed in landscapes with varying distribution and number of cells containing food. Dispersal generally increased as the number of patches with food increased, however, rovers and sitters adopted similar dispersal strategies when food was fixed and limited. Conversely, their strategies differed when the total amount of food increased with the number of patches. We find that both the inter-patch distance and distribution can influence dispersal. However, the effect of inter-patch distance and distribution on dispersals depends on genotype × environment interaction. Our findings highlight the importance of considering G × E when assessing how dispersal strategies and landscape dynamics influence the distribution of animal communities.     

Social Environment Influences Performance in a Cognitive Task in Natural Variants of the Foraging Gene

In Drosophila melanogaster, natural genetic variation in the foraging gene affects the foraging behaviour of larval and adult flies, larval reward learning, adult visual learning, and adult aversive training tasks. Sitters (for ^s) are more sedentary and aggregate within food patches whereas rovers (for^R) have greater movement within and between food patches, suggesting that these natural variants are likely to experience different social environments. We hypothesized that social context would differentially influence rover and sitter behaviour in a cognitive task. We measured adult rover and sitter performance in a classical olfactory training test in groups and alone. All flies were reared in groups, but fly training and testing were done alone and in groups. Sitters trained and tested in a group had significantly higher learning performances compared to sitters trained and tested alone. Rovers performed similarly when trained and tested alone and in a group. In other words, rovers learning ability is independent of group training and testing. This suggests that sitters may be more sensitive to the social context than rovers. These differences in learning performance can be altered by pharmacological manipulations of PKG activity levels, the foraging (for) gene''s gene product. Learning and memory is also affected by the type of social interaction (being in a group of the same strain or in a group of a different strain) in rovers, but not in sitters. These results suggest that for mediates social learning and memory in D. melanogaster.     

Foraging Behavior and Patch Time Allocation by Fopius arisanus (Hymenoptera: Braconidae), an Egg-Larval Parasitoid of Tephritid Fruit Flies

This study quantitatively describes the host-searching behavior of Fopius arisanus (Sonan) (Hymenoptera: Braconidae), an important egg-larval parasitoid of tephritid fruit fly pests, on coffee berries infested with host eggs of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). We also investigate the parasitoid's response to local variation in host patch quality. The temporal pattern of behavioral organisation was examined by constructing an ethogram. The parasitoid spent over 90% of its foraging time in detecting and locating hosts after arriving on a host-infested fruit, and displayed a relatively fixed behavioral pattern leading to oviposition. Patch residence time increased in the presence of host-associated cues, following successful ovipositions, and with increasing size of host clutches per fruit, but decreased with each successive visit to the same host patch and with increasing availability of alternative host patches. The parasitoid females discriminated against previously parasitized hosts and spent significantly less time and searching effort on patches previously exploited by herself or by conspecific females. The effective host-searching behavior, perfect host discrimination ability, and success-motivated searching strategy shown by F. arisanus ensured a thorough exploitation of host resources by this parasitoid.     

Search duration ofDrosophila melanogaster on Homogeneous sucrose patches: Relative effects of starvation period,sucrose concentration and patch size

Search duration of adultDrosophila melanogaster on homogeneous sucrose patches increased with the period that flies were starved, the concentration of sucrose which they ingested, and the size of a patch onto which they were released. Since in all conditions the sucrose concentration tested in patch experiments was above the taste threshold, the results indicate that a fly has a set of rules for specifying search duration that integrates external information (resource quality and size) and internal information (period of starvation).     

Do Larger Fruits Provide a Partial Refuge for Rose-Hip Flies Against Parasitoids?

The preference of insect herbivores to oviposit into larger structures might be explained by the superior food resource a larger structure offers to herbivore offspring or as an adaptive strategy by the herbivore to protect its offspring against parasitoids, should larger structures provide a partial refuge against parasitoids. We investigated whether larger fruits provide a partial refuge for rose-hip fly (Rhagoletis basiola) offspring against the specialist parasitoid Halticoptera rosae. We tested whether female parasitoids exhibit a preference to land on larger rose-hips into which females of the host fly prefer to oviposit and whether parasitoids are less successful in locating host eggs on large, compared to small, fruits. Female parasitoids showed no clear preference for larger fruits. When searching fruits, they were about equally successful in locating fly eggs on large and small fruits, with a slight, though nonsignificant trend for fly offspring in large fruits to be located more easily. Furthermore, wasps did not require more time to locate host eggs on large fruits than on small fruits, suggesting a nonrandom searching behavior. Consequently, large rose-hips do not provide a partial refuge to fly offspring and the preference of flies to oviposit into larger fruits cannot be explained as an adaptation against parasitoid searching efficiency.     

Influence of intertree distance on foraging behaviour of Rhagoletis pomonella in the field

Abstract. 1. We tested a prediction from contemporary foraging theory that animals should decrease their allocation of energy to the searching of individual patches when interpatch travel costs decrease.
2. We used individual Rhagoletis pomonella Walsh (Diptera: Tephritidae) females foraging for oviposition sites (= Crataegus fruit) in a host tree which was surrounded by four other trees at varying distances.
3. We found that flies generally invested less search, measured as time spent searching a tree or number of leaves visited on a tree, when neighbouring trees were nearby than when farther away.
4. Under our test conditions, flies appeared to have difficulty locating neighbouring trees at a distance of more than 1.6 m.
5. Our study calls into question the interpretation of search effort by insects within resource patches in the absence of information on interpatch distances.     

Sources of information controlling motor patterns in arthropod local search orientation

Search orientation is controlled by information that is stored genetically, idiothetically or through learning and that is gained from internal and external sensory systems. Sources of variation in motor patterns could derive from any of the types of information, or could originate during the execution of the instructions derived from orientation information. Local search after resource utilization in the flies Musca demestica and Drosophila melanogaster can be addressed as an initial increase in turning rate and decrease in locomotory rate, followed by a transition in both measures to a lower turning rate and a higher locomotory rate characteristic of ranging. The search tactic of flies promotes accrual of discrete resources in a patch. A forward-moving tendency, combined with a “noisy” looping motor pattern, enhances resource-finding in both linear and non-linear resource patterns. The period before a fly leaves a patch—its giving-up-time—is a function of current resource density and the slope of the transition from local search to ranging: once a fly switches to the relatively straight path characteristic of ranging, the chances of it leaving the patch depends on whether or not another resource is encountered. Duration of local search is dependent on the genotype of an individual, level of starvation or satiation, resource quality (sucrose concentration) and quantity (patch size) and presence of resource-specific sensory information.     

Animal response to nested self-similar patches: a test with woolly bears

To gain insight into how animals respond to resource patchiness at different spatial scales, we envision their responses in environments comprised of nested, self-similar patches. In these environments, all resources reside within the smallest patches, and resource density declines as a constant exponent of patch size. Accordingly, we use simple mathematical formulations to describe a self-similar environment and a null model of how animals should respond to this environment if they do not perceive resource distribution. We then argue that animals that can perceive resource distribution should partition space by reducing the relative time searching between patches as patch size increases. On an experimental landscape, we found that woolly bear caterpillars Grammia geneura could partition space in this manner, but the range of patch sizes over which they did so tended to increase with resource aggregation. Nevertheless, scaling efficiency (i.e. the scaling of search time versus the scaling or resource density) was similar in all distributions when averaged over all patch sizes. These disparate patterns with similar outcomes resulted from differences in caterpillars' abilities to discriminate spatially among patches of different sizes via their movement pathways, and differences in their use of speed to detect resource items. Our work is relevant to the characterization of resource availability from an animal's perspective, and to the linking of optimal foraging theory to the modeling of search behavior.     

Patch size effects are more important than genetic diversity for plant–herbivore interactions in Brassica crops

1. Considerable evidence suggests that the diversity within plant communities may strongly affect the strength of species interactions, but the majority of studies only considered interspecific diversity. 2. This paper examines the effect of intraspecific genetic diversity within Brassica fields on two Brassica specialists, cabbage root fly, and diamondback moth, and on a parasitoid attacking diamondback moths. Genetic diversity was manipulated both in a replacement and an additive design. 3. Both herbivore densities and parasitism rates were higher in smaller plots, with limited responses to increased within‐plot diversity. All species showed variable densities across genotypes, and preference hierarchies were species specific. 4. Responses to plot size in root flies scaled with the diameter‐to‐area ratio, suggesting that patch detectability affected local density, whereas responses by diamondback moths and parasitoids deviated from this ratio. These species differences could be traced to differences in the residence time within patches, where diamondback moths typically spend longer and more variable time periods in patches than root flies. 5. The lack of response to genetic diversity by both herbivores suggests that egg‐laying rates are affected by decisions on the plant and not by attraction from a distance, neither to the plant itself nor the patch. Patterns of differential attack may then be due to different acceptability for studied genotypes. 6. Future theories on insect responses to spatial heterogeneity should focus on species traits and how traits interact with information landscapes in the field.     

Catching Ariadne by her thread: how a parasitoid exploits the herbivore's marking trails to locate its host

Chemical signals that can be associated with the presence of a host insect often work as arrestants in close range host location by parasitoids, leading to longer searching times on patches where such signals are present. Our current view of parasitoid host location is that by prolonging the search times in patches, randomly searching parasitoids enhance their chance of detecting host insects. However, prolonged search times are not necessarily the only modification in parasitoid behaviour. In this study, we examine the exploitation of host-fruit marking pheromone of rose-hip flies, Rhagoletis basiolaOsten-Sacken (Diptera: Tephritidae) by the specialized egg-larval parasitoid Halticoptera rosae Burks (Hymenoptera: Pteromalidae). We provide evidence that the instantaneous probability that a host egg will be located by a searching parasitoid wasp differs markedly between pheromone-marked and unmarked fruits. The arresting response to the marking pheromone, i.e., the prolonged time a wasp is willing to search on marked fruits, can only account for a small fraction of the difference in successful host location on marked and unmarked fruits. We further demonstrate that the time wasps require to locate the host egg is independent of the size of the rose-hip harbouring the fly egg, and thus is independent of the area the wasp potentially has to search. A comparison of our findings with results of different search algorithms for parasitoid wasps suggests that wasps use the fly's pheromone marking trail as a guide way to the fly's oviposition site and thus the host egg.     

Cooperation between Drosophila flies in searching behavior

In Drosophila melanogaster food search behaviour, groups of flies swarm around and aggregate on patches of food. We wondered whether flies explore their environment in a cooperative way as interactions between individual flies within a population might influence the flies' ability to locate food sources. We have shown that the food search behavior in the fruit fly Drosophila is a two-step process. Firstly, 'primer' flies search the environment and randomly land on different food patches. Secondly, the remaining group of flies move to the most favorable food source and aggregate there. We call this a 'search–aggregation' cycle. Our data demonstrate that flies do not individually assess all available food resources. Rather, social interactions between flies appear to affect their choice of a specific food patch. A genetic analysis of this 'search–aggregation' behavior shows that flies carrying mutations in specific genes (for example, the dunce ( dnc ) gene which codes for a phosphodiesterase) were defective in this search–aggregation behavior when compared to normal flies. Future investigations of the neuronal signaling involved in this behavior will help us to understand the complexities of this aspect of Drosophila social behaviour.     

Interference competition in central place foragers: the effect of imposed waiting on patch-use decisions of eastern chipmunks, Tamias striatus

When central place foragers compete aggressively for patchyresources, subordinates may be preventedfrom collecting fooduntil a dominant has departed with its load. Extensions of centralplace foraging models predict that animals forced to wait ata patch should increase their load sizes and patch times aswellas their tendency to search for and switch to alternative patches.We tested these predictions usingeastern chipmunks, Tamias striatus,hoarding sunflower seeds collected from seed/vermiculite mixturesintrays placed 5-8 m from their burrows. By using her hand toprevent access to the patch, the experimentersubjected animalsto progressively increasing waiting times at two seed densities;another series of trialsat the same seed densities monitoreda similar number of trips without imposed waiting. As predicted,patch times and load sizes were higher in sessions with imposedwaiting than in control sessions. Loadsizes increased with trialnumber in experimental sessions but decreased or remained thesame in controlsessions. Chipmunks spent more of their timesearching for alternative patches during trials with imposedwaiting than during controls. They also started searching foralternative patches at lower levels of imposed waiting whenusing poor than when using rich patches. These results indicatethat the effects of interference on foraging decisions and onspatial overlap between individuals can be predicted by simpleeconomic models. Furthermore, the results suggest how resource-defensetactics can be predicted by the economic effects of interferenceon the foraging efficiency of the opponent.     

Interactions between searching strategies ofDrosophila parasitoids and the polymorphic behavior of their hosts

Two strains of Drosophila melanogaster, rover and sitter, differing in locomotion while foraging were simultaneously exposed to females of either Leptopilina boulardi or Ganaspis xanthopoda (parasitic Hymenoptera). These two parasitoids show different modes of host-searching behavior, ovipositor searching, or vibrotaxis, respectively. L. boulardi parasitized the sitter host strain significantly more than the rover. In contrast, G. xanthopoda parasitized the rover strain more than the sitter. In one case, L. boulardi selected far more sitters than rovers in population cage experiments. We also describe the frequencies of rovers and sitters in three natural populations where the local parasitoid community may have partially contributed to the differences in rover and sitter frequencies.     

Giving-up time variation in response to differences in nectar volume and concentration in the giant tropical ant,Paraponera clavata (Hymenoptera: Formicidae)

Giving-up times in resource patches by workers of the giant tropical ant,Paraponera clavata, are associated with travel time and reward volume but not reward concentration. The discovery of an artificial nectar reward stimulates local search which is centered around the initial reward site. Longer giving-up times increase the likelihood that a worker will find a second reward, but the search appears to be more effective for renewed rewards at the same location than for nearby rewards. When workers are near the colony, larger rewards cause the workers to stop searching and to initiate recruitment behavior. At patches distant from the nest, the threshold in reward volume for recruitment is much higher. These results are consistent with expectations for search strategies when energy expenditure in search is minimal, resources are renewable, and recruitment can occur.     

The use of visual information by house flies,Musca domestica (Diptera: Muscidae), foraging in resource patches

Summary House flies, Musca domestica, respond to visual contrasts on the substrate if a resource is associated with the contrasting patterns. Visible resource patch boundaries serve as a signal to flies that they are about to leave a rewarding patch. Searching flies respond to such visual information by walking along the resource patch boundary and turning back into the patch at its edge. This edge detection and response serve as a mechanism for flies with visual cues to stay in a rewarding patch and locate more resources within it. The intensity of their response correlates with the quality of the resource. In the absence of visual cues, patch shape affects foraging success; flies find more resources in circular than in linear resource distributions. The effects of visual cues, however, render patch shape unimportant. Various substrate contrasts are effective as resource information for flies: dark (e.g., green) figures on bright (e.g., white) backgrounds or bright figures on dark backgrounds. Responses to substrate contrasts measured in this study indicate that, over the short term, house flies can learn a visual cue associated with a food source.     

Natural selection in the laboratory for a change in resistance byDrosophila melanogaster to the parasitoid waspAsobara tabida

The selection response of the polymorphic hostD. melanogaster (Meigen) to the braconid waspA. tabida (Nees) is addressed. Cages of flies with and without wasps were initiated with a population ofD. melanogaster that exhibited variation both in larval foraging behavior and in encapsulation ability. Encapsulation ability was measured as the proportion of parasitized larvae that produce a hardened capsule which encapsulates the wasp egg and ultimately kills the wasp larva. We determined whether the host population changed its encapsulation ability and/or its foraging behavior in response to the wasp. Both species were collected from a local orchard whereA. tabida is the only wasp known to parasitizeD. melanogaster larvae. The naturally occurring genetic polymorphism for rover and sitter larval foraging behavior inD. melanogaster is also found in this field population.A. tabida's vibrotactic search behavior enables it to detect rover more frequently than sitter larvae. Rover larvae move significantly more while feeding than do sitter larvae. In this field population, rover larvae also show higher encapsulation abilities than do sitter larvae. Six cage populations, three without wasps and three with wasps, each containing an equal mixture of rover and sitter flies, were established in the laboratory and maintained for 19 fly generations. Selection pressure in the laboratory was similar to that found in the field population from which the flies and wasps were derived. We found that larvae from cages with wasps developed a significantly higher frequency of encapsulation than those reared without wasps. We were, however, unable to detect a change in larval movement (rover or sitter behavior) in larvae from cages subject to selection from wasps compared to larvae from cages containing no wasps. This may have resulted from a balance between two selective forces, selection against rovers by the wasps' use of vibrotaxis, and selection for rovers resulting from their increased encapsulation abilities     

Population densities and density–area relationships in a community with advective dispersal and variable mosaics of resource patches

Many communities comprise species that select resources that are patchily distributed in an environment that is otherwise unsuitable or suboptimal. Effects of this patchiness can depend on the characteristics of patch arrays and animal movements, and produce non-intuitive outcomes in which population densities are unrelated to resource abundance. Resource mosaics are predicted to have only weak effects, however, where patches are ephemeral or organisms are transported advectively. The running waters of streams and benthic invertebrates epitomize such systems, but empirical tests of resource mosaics are scarce. We sampled 15 common macroinvertebrates inhabiting distinct detritus patches at four sites within a sand-bed stream, where detritus formed a major resource of food and living space. At each site, environmental variables were measured for 100 leaf packs; invertebrates were counted in 50 leaf packs. Sites differed in total abundance of detritus, leaf pack sizes and invertebrate densities. Multivariate analysis indicated that patch size was the dominant environmental variable, but invertebrate densities differed significantly between sites even after accounting for patch size. Leaf specialists showed positive and strong density–area relationships, except where the patch size range was small and patches were aggregated. In contrast, generalist species had weaker and variable responses to patch sizes. Population densities were not associated with total resource abundance, with the highest densities of leaf specialists in sites with the least detritus. Our results demonstrate that patchy resources can affect species even in communities where species are mobile, have advective dispersal, and patches are relatively ephemeral.     

The arrangement of resources in patchy landscapes: effects on distribution, survival, and resource acquisition of chironomids

The spatial arrangement of resources in patchy habitats influences the distribution of individuals and their ability to acquire resources. We used Chironomus riparius, a ubiquitous aquatic insect that uses leaf particles as an important resource, to ask how the dispersion of resource patches influences the distribution and resource acquisition of mobile individuals in patchy landscapes. Two experiments were conducted in replicated laboratory landscapes (38×38 cm) created by arranging sand and leaf patches in a 5×5 grid so that the leaf patches were either aggregated or uniformly dispersed in the grid. One-day-old C. riparius larvae were introduced into the landscapes in one of three densities (low, medium, high). In experiment 1, we sampled larvae and pupae by coring each patch in each landscape 3, 6, 12, or 24 days after adding larvae. In experiment 2, emerging adults were collected daily for 42 days from each patch in each landscape. In aggregated landscapes, individuals were aggregated in one patch type or the other during a particular developmental stage, but the ”preferred” type changed depending on developmental stage and initial density. Adult emergence was lower by about 30% in all aggregated landscapes. In dispersed landscapes, individuals used both types of patch throughout their life cycles at all initial densities. Thus, patch arrangement influences the distribution of mobile individuals in landscapes, and it influences resource acquisition even when average resource abundance is identical among landscapes. Regardless of patch arrangement, high initial density caused accumulation of early instars in edge patches, 75% mortality of early instars, a 25% increase in development time, and a 60% reduction in adult emergence. Because mortality was extremely high among early-instar larvae in high-density treatments, we do not have direct evidence that the mechanism by which patch arrangement operates is density dependent. However, the results of our experiments strongly suggest that dispersion of resource patches across a landscape reduces local densities by making non-resource patches available for use, thereby reducing intraspecific competition. Received: 20 July 1999 / Accepted: 28 January 2000