Area-restricted Search Behaviour Research Articles

Density-dependent parasitism of Delphacodes kuscheli eggs by Anagrus flaveolus: Influence of egg patchiness and density

Many herbivorous insects display a marked tendency to aggregate and previous work has shown that the parasitoids likely to be more effective for pest control programs are those that concentrate their attacks on denser host patches. However, as herbivore density changes different spatial patterns usually emerge in their distribution. In Tucumán province, Argentina the mymarid Anagrus flaveolus is a native egg parasitoid of Delphacodes kuscheli, which oviposits endophitic eggs and is the only demonstrated vector of the MRCV virus that seriously affects maize (Zea mays). Winter is the critical period for maize colonization from oat (Avena sativa) crops where D. kuscheli overwinters. We analyzed, under field conditions and during the winter critical period, percentage parasitism by A. flaveolus when host patch density increases following two different patterns: an increase in the batch size, and an increase in the number of infested plants with similar mean batch size. In order to generate a heterogeneous egg patchiness, 144 oat plants were arranged in 36 groups of four plants each, and four types of groups were created by placing one, two, three or four infested plants per group. Each group was characterized by the number of infested plants as well as by the number of eggs. If one, two, three or all four plants were infested, the group was denominated G1, G2, G3 or G4, respectively. Considering only G1, the number of eggs per group increased only if the batch size increased. On the other hand, considering all G1, G2, G3 and G4 groups, the increase in patch density from G1 to G4, was essentially due to an increase in the number of infested plants. The groups were symmetrically distributed in the field in a homogeneous 200-m2 area (the position of each group was randomly assigned), and allowed for oviposition for 48 h since A. flaveolus only attacks eggs that have three or less days of development. We found that almost all infected plants were parasitized by A. flaveolus but parasitism never surpassed 64% of the available eggs, suggesting that the parasitoid selectively attacks eggs inserted in particular places of the oat plant, and/or never saturates a batch. We also found that parasitism was spatially direct density dependent when only G1 was considered, as well as when G1, G2, G3 and G4 were considered together. In the first case, an increase in the number of eggs in a group of four plants represents an increase in the batch size, and higher batch size received higher parasitism. In the second case, it represents an increase in the number of infested plants, and higher patch density received higher parasitism. Although the proportion of infected plants parasitized was similar, infected plants with similar number of eggs received higher parasitism when placed in denser groups (G3 and G4) than when placed in the less dense groups (G1 and G2). Behavioral mechanisms leading to a restriction on re-dispersal, like an area-restricted search behavior, as well as supernormal stimulus of contiguous host egg batches in certain places that may require a higher threshold before mutual interference has an effect, could be explained these results.

Searching Behavior ofColeomegilla maculataLarvae Feeding on Colorado Potato Beetle Eggs

Abstract Coleomegilla maculataDeGeer (Coleoptera:Coccinellidae) fourth instars were placed singly into a searching arena containing either 1 or 4 potato (Solanum tuberosumL.) plants, with a total leaf area (both sides) of approximately 0.20 m2per plant. Prey were approximately 24-h-old eggs ofLeptinotarsa decemlineata(Say) (Coleoptera: Chrysomelidae). Three egg densities were used: 2 egg masses per 4 plants (i.e., 2.5 egg masses/m2of leaf area), 2 egg masses per 1 plant (i.e., 10 egg masses/m2), and 7 egg masses per 1 plant (i.e., 35 egg masses/m2). Predators were observed for 4 h. Time spent in selected behaviors (searching, feeding, resting) and location in the plant canopy during each behavior were recorded. Predators exhibited both extrinsic and area-restricted search behaviors. Predators searched a greater amount of leaf area and for longer time periods at 2.5 egg masses/m2compared to 10 or 35 egg masses/m2. Successful predators consumed approximately 8 eggs during the 4-h period and the handling time was approximately 8 min per egg.C. maculatafourth instars consumed entire eggs when they initiated feeding; subsequent eggs were partially consumed. At 10 and 35 egg masses/m2, predators successfully finding eggs spent more time resting than did predators at 2.5 egg masses/m2.

Experiments and a model examining learning in the area-restricted search behavior of ferrets (Mustela putorius furo)

Area-restricted searches have been described u important components of the foraging behavior of many organisms. It is unclear, however, whether individual foragers can use learning to fine-tune their searches, or even whether these searches are efficiently performed. I used a simulation model to make qualitative predictions about search behavior in a laboratory system. The simulation model indicates that the sinuosity and path length of searches strongly affect search efficiency. The model predicts that, for a rate-maximizing forager, path length should increase and search sinuosity should decrease as become less dumped. Foraging animal* may therefore be selected to learn the path length and sinuosity of searches in response to changing degrees of dumping of prey. These predictions were tested in a laboratory system involving ferrets (Mustela putorius furo) foraging for oil-drop prey items. Search paths changed in a graded manner to experimental manipulations of the dumping of prey. As predicted by the model, ferrets learned to perform longer and less sinuout search paths as became less dumped. This study provides the first evidence that area-restricted search behavior is learned and can be fine-tuned to efficiently exploit different spatial distributions of food.

Innate movement rules in foraging bees: flight distances are affected by recent rewards and are correlated with choice of flower type

The non-random movement patterns of for- aging bees are believed to increase their search eƒ- ciency. These patterns may be innate, or they may be learned through the bees' early foraging experience. To identify the innate components of foraging rules, we characterized the flight of naive bumblebees, foraging on a non-patchy "field" of randomly scattered artificial flowers with three color displays. The flowers were ran- domly mixed and all three flower types o⁄ered equal nectar volumes. Visited flowers were refilled with prob- ability 0.5. Flight distances, flight durations and nec- tar probing durations were determined and related to the bees' recent experiences. The naive bees exhibited area-restricted search behavior, i.e., flew shorter distances following visits to rewarding flowers than after visits to empty flowers. Additionally, flight dis- tances during flower-type transitions were longer than flight distances between flowers of the same type. The two movement rules operated together: flight distances were longest for flights between flower types following non-rewarding visits, shortest for within- type flights following rewarding visits. An increase in flight displacement during flower-type shifts was also observed in a second experiment, in which all three types were always rewarding. In this experiment, flower- type shifts were also accompanied by an increase in flight duration. Possible relationships between flight distances, flight durations and flower-type choice are discussed.