Tuyosi Sugimoto

Foraging for patchily-distributed leaf-miners by the parasitoid,Dapsilarthra rufiventris (Hymenoptera: Braconidae). II. Stopping rule for host search

We studied the stopping rule which the female parasitoid,Dapsilarthra rufiventris, uses for deciding when to leave the leaflet on which she is searching for leaf-mining larvae,Phytomyza ranunculi. She is unlikely to employ some current stopping rules, such as fixed-number and fixed-time rules and others. The searching female appears to deposit a marking pheromone on the leaflet. We formulated a model for predicting the amount of pheromone accumulated on the leaflet. The model assumes that she will deposit the pheromone on the leaflet at a given rate (a) per unit time which is proportional to search speed, and will leave it when the amount of pheromone reaches the thresholdL. In this modelL denotes the amount of the search effort spent on the leaflet. The model was fitted fairly well to the data. A comparison of the observed results with the predictions of the model suggests thatL increases markedly at the first encounter with the mine and at a lower rate for the subsequent encounters. This appears to be a kind of area-concentrated search, that is, searching for hosts for a while in the immediate vicinity after finding one host, and would be adaptive in foraging forP. ranunculi larvae, which exhibit clumped distributions among leaflets in the field.

Foraging for patchily-distributed leaf miners by the parasitic wasp,Dacnusa sibirica

We studied the rules used by the female parasitoid,Dacnusa sibirica Telenga (Hymenoptera: Braconidae), for deciding when to leave a tomato leaflet on which she is searching for larvae of the leafminer,Liriomyza bryoniae Kalt. (Diptera: Agromyzidae). Females would deposit a marking pheromone on the leaflet and would leave the leaflet when the amount of the pheromone accumulated to the thresholdL, which is proportional to the amount of search effort on the leaflet.L appears to increase with host density since it rises after every encounter with a host (or mine).D. sibirica would employ an area-concentrated search, which is advantageous in foraging for hosts showing a clumped distribution.

Stopping rule of host search by the parasitoid,Chrysocharis pentheus (Hymenoptera: Eulophidae), in host patches

We studied the stopping rule obeyed by the female parasitoid,Chrysocharis pentheus, in deciding when to leave the leaflet on which she is searching for larvae ofPhytomyza ranunculi. She seemed not to employ some stopping rules that have been suggested; i.e., a fixed-number rule and a fixed-time rule and others. The stopping model formulated forDapsilarthra rufiventris parasitic on the same host species fitted well to the results. The model assumes that the searching female will deposit a marking pheromone on the leaflet at a rate proportional to the search speed and will leave the leaflet when the amount of the pheromone that has accumulated on the leaflet reaches the threshold,L. In this model,L denotes the amount of search effort spent on the leaflet. A comparison of the observed results with the predictions from the model suggested thatL increased markedly at the first encounter with the mine (host), but less at later encounters.C. pentheus appears to employ a mixed strategy of a fixed search-effort and an area-concentrated search. This would confer an adaptive advantage in foraging forP. ranunculi larvae, which are distributed in clumps among leaflets in the field.

Models of the spatial pattern of egg population of ranunculus leaf mining fly, Phytomyza ranunculi (Diptera: Agromyzidae), in host leaves.

This paper considers two kinds of model of the spatial pattern of egg distribution of the Ranunculus leaf mining fly,Phytomyza ranunculi Schrank, as a step to determining the effect of the distribution upon the parasitism of this species by the eulophid parasite,Kratochviliana sp.. Each model incorporates submodels in several important stages of both the processes of visiting and subsequent oviposition by the fly. Model 2 is more general than model 1, because the former also includes the effect of oviposition restraint. Both models fitted well the egg distribution on fresh plants and on exploited plants. The fitting similarity on exploited plants is due to the fact that there were not so many heavily exploited leaves which lead to oviposition restraint, owing to the low density of mature larvae contained in the leaves. These models will be applicable to the distribution of larvae as well as eggs, because most larvae remain in the leaf where they occurred as eggs, until emerging just before pupation. This paper also discusses by use of these models the fact that this fly tends to effectively avoid excessive oviposition in leaves by laying fewer eggs per visit and visiting leaves more sparsely and also by refraining from further oviposition on leaves exploited heavily by mature larvae.

Responses to the host mine by two parasitic wasps,Dapsilarthra rufiventris (Hymenoptera: Braconidae) andChrysocharis pentheus (Hymenoptera: Eulophidae)

Larvae of a ranunculus leaf-mining fly, Phytomyza ranunculi Schrank, mainly feed on the palisade parenchyma of the leaflet of the host plant, and produce a serpentine mine. It appears as a white linear pattern under the upper surface of the leaflet (Fig. 1), in which the epidermis serves as the roof for the mine (Hering 1951). The mine produced by a single matured (3rd-instar) larva is on the average 10 cm long, 1.5 mm at the widest and 1.3cm 2 in area (Sugimoto 1971). These larvae are attacked by many species of parasitic wasps in the field (Sugimoto 1983). These parasitoids appear to employ the mine as an important cue not only to the host-patch location (Sugimoto et al. 1988) but also to the host location on the leaflet (Sugimoto 1977; Kato 1984; Sugimoto et al. 1986). After landing on the leaflet, the female braconid (Ichneumonoidea) wasp, Dapsilarthra rufiventris (Nees) (Dr for short in this text), first searches for the mine, and once having found it, searches in turn for the host larva along it, frequently palpating with her antennae and frequently probing with her ovipositor (Sugimoto et al. 1986) (Fig. 2,A). Also, when nearing the spotlike mine (ca. 1 mm wide) made by the larva soon after hatching, she directs herself toward it, often making motionless stops and, repeatedly palpating the mine with her antennae and/or probing it with her ovipositor. During the motionless stops she may perceive the vibration of the leaflet emitted when the young host chews the leaftissue (Sugimoto et al. 1988). Conversely, the female of the eulophid (Calcidoidea) wasp, Chrysoeharis pentheus Walker, (Cp for short in thfs text), ignores the spot-like mines, and when encountering the developed mine produced by the 2ndor 3rd-instar larva, walks more closely along the mine frequently palpating with her antennae (Fig. 2,B), but unlike Dr she has no habit of frequently probing the mine with her ovipositor. Only when reaching the host, does she exhibit this behaviour, probably as a means of confirming the suitability of the host (Sugimoto 1977). According to the classification of the searching modes of wasps parasitic on Drosophila larvae by Vet & van Alphen (1985), Cp appears to employ the antennal search, while Dr is likely to use the mixed modes of the antennal search, the ovipositor search and probably vibrotaxis. We conducted experiments to establish what properties of the host mine these parasitoids respond to when searching on leaflets. All the experiments in this study were carried out under the conditions of 23~ 70 % RH and fluorescent lighting. Both host flies and Dr adults were obtained from a laboratory culture, while Cp adults were reared from plants injured by hosts in the field. The test material was placed m a transparent plastic cylinder (10x20 cm) and the female wasp was released on the test material. Some females were used in individual treatments. The criteria for deciding ff they responded to the experimental treatments were based on characteristics of their searching behaviour described above. For Dr, this behaviour was walking along the mine, palpating with her antennae and probing with her ovipositor. For Cp, this behaviour was walking more than 1 cm along the mine while frequently palpating. We decided that they responded to the mine when the above responses occurred 2 times or more per 10 trials. The detailed procedures in each experiment are described as needed in the following section.

Host-attacking behavior of a eulophid parasite,Kratochviliana sp., to the leaf mining host,Phytomyza ranunculi (Diptera: Agromyzidae) during its stay on the leaf

The present paper studies how the female parasite ofKratochviliana sp. visits and attacks its host larvae of Ranunculus leaf mining fly,P. ranunculi at a single leaf visit. The parasite visited its hosts at random on the leaf. The frequency of host visits was independent of the host density and the proportion of hosts survived from the parasite attack, in a leaf and its distribution was expressed as a single straight line. It almost always attacked living hosts at the first host visit after isolated from them for one day but with the rate of about 0.5 at the subsequent visits. In consequence, the relationships of the number of host attacks and killed hosts to the host density drew satulated curves in each. A model of host attack by this parasite at its single leaf visit was formulated by modifyingBakker et al.s model (1972) basing upon these observations and the attack avoidance by the parasite to already attacked hosts previously reported.