The effect of prey size and prey density on the functional response, survival, growth and development of a predatory pentatomid bug,Podisus maculiventris say

Summary Two experiments on the nymphal predation ofPodisus maculiventris were conducted usingSpodoptera litura larvae as prey. First experiment: The predator nymphs divided into three groups were reared individually from second instar to adult in a small vessel. Each nymph in the groups 1, 2 and 3 was allowed to attack the serially growing larvae (these were supplied at the rate of one per day) from 3-, 5- and 7-day old after hatching, respectively. The first prey used for the group 1 was so small that it was not only insufficient to satiate the predator but also was difficult to be searched out. But these disadvantages were soon recuperated due to the rapid growth of the prey and all nymphs could survive to adults. The survival rate of third and fourth instar nymphs in the group 3 was severely affected by vigorous counterattack of older prey larvae. Second experiment: The predator nymphs were individually reared either in a small vessel or in a large one at various rates of food supply (the prey larvae of 7-day old were used). The functional response curves obtained for each instar of the predator took a saturation type within a certain range of the prey density. The saturation level specific to each instar was generally higher for the predator reared in the large vessel than in the small one. The functional response of fourth and fifth instar nymphs was accelerated at a high prey density,viz. 16 larvae per vessel. Even at the low rate of food supply,viz. one larva per day per predator, the predator nymphs could survive to adults, but the size of resultant adults were abnormally small.     

Simulation model of a predator-prey system comprised ofPhytoseiulus persimilis andTetranychus urticae. II. Model sensitivity to variations in the life history parameters of both species and to variations in the functional response and components of the numerical response

Summary A detailed sensitivity analysis of a model of a predator-prey system comprised ofTetranychus urticae andPhytoseiulus persimilis was performed. The aim was to assess the relative importance of the life history parameters of both species, the functional response, and the components of the numerical response. In addition, the impact of the initial predator-prey ratio and the timing of predator introduction were tested. Results indicated that the most important factors in the system were relative rates of predator and prey development, the time of onset of predator oviposition, and the mode of the predator's oviposition curve. The total oviposition of the predator, the effect of prey consumption on predator oviposition, and predator searching were important under some conditions. Factors of moderate importance were the adult female predator's functional response, total prey oviposition, the mode of the prey's oviposition curve, abiotic mortality of the pre-adult predator, and the effect of prey consumption on predator development and on the immature predator's mortality. Factors of least importance were the variances of the predator's and prey's oviposition curves, the abiotic mortality of the adult predator, the abiotic mortality of the pre-adult and adult prey, the functional response of the nymphal and adult male predators, and the effect of prey consumption on adult predator mortality. The sex ratios had little effect, except when the proportion of female predators was very low. The initial predator-prey ratio and time of predator introduction had significant impacts on system behavior, though the patterns of impact were different.     

Functional response and searching efficiency inPseudogonatopus flavifemur Esaki and Hash. (Hymenoptera: Dryinidae), a parasite of rice planthoppers

Summary The functional response ofPseudogonatopus flavifemur E & H (Hym., Dryinidae) was investigated by offering hosts (brown planthopper) at densities ranging from 8 to 160 per cage. The response curve was found to be sigmoid, i. e.Holling's (1959) Type III curve. In experiments involving 310 hosts per cage distributed unevenly in 5 densities (10, 20, 40, 80 and 160 per hill), and a different female parasite density each time (viz. 1, 2, 4, 8 or 16 per cage), the behavioral response was described well by the “random predator equation” ofRoyama (1971) andRoger (1972), which is a convex exponential curve. The area of discovery (a) decreased with an increase in female parasite density (P), and the relationship was described by the equation: loga=−1.0099−0.3638 logP. There was an apparent increase in handling time per host as the number of female parasites increased. Superparasitism, a rare phenomenon under natural conditions, was often observed in the laboratory. The potential ofP. flavifemur as a biocontrol agent of the brown planthopper is discussed.     

Predator-prey system structure in patchy and ephemeral phytotelmata: Aquatic communities in small aroid axils

Mechanisms allowing the persistence of an aquatic predator-prey system in tiny pools (the mean ca. 0.5 ml) held by taro axils were analyzed from the viewpoint of temporal and spatial patterns of habitat use. Predatory larvae of a mosquitoTopomyia tipuliformis concentrated in young axils, while 9 other taxa utilized both young and old axils or concentrated more in older axils. The total prey density was lower in axils with the predator but the density of each prey taxon (except for a few cases) and the number of prey taxa did not differ between axils with and without predators. This indicates thatT. tipuliformis is a general predator and does not influence prey community organization through selective removal of particular prey taxa. Inter-axil distribution ofT. tipuliformis was aggregated in the first instar but uniform in the third and fourth instars due to intraspecific cannibalism, which assures the survival of a single individual under short food supply. Distributions of prey taxa were mostly aggregated, fitting the negative binomial distribution. Thirty seven out of 45 associations of 10 taxa were independent with 3 negative (between the predator and some late-colonizing prey) and 5 positive (between some prey taxa) associations. Probabilistic refuges (produced by independent aggregated distributions) reduced interspecific encounters which may result in competition and predation, and thus probably facilitated prey coexistence. There was no evidence for the importance of predation in structuring the prey community. This system may be prey-dominated in that predator persistence depends on prey community existence but prey community structure depends less on predation.     

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

Summary 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. Ecological studies on the relationship between Ranunculus leaf mining fly,Phytomyza ranunculi Schrank (Diptera; Agromyzidae) and its parasite,Kratochviliana sp. (Hymenoptera; Eulophidae) from the viewpoint of spatial structure II. This paper constitutes a part of the Doctoral Thesis presented to the College of Agriculture, Kyoto University by the present author.     

An acarine predator-prey population infesting roses

Summary WhenPhytoseiulus persimilis was reared withTetranychus urticae, infesting roses propagated in a greenhouse at controlled daily temperatures of 24°C (12 hrs) and 18°C (12 hrs), prey numbers fluctuated with peaks of increasing amplitude. Differential dispersal of prey and predator species was one factor contributing to the inability of the natural enemy to control the pest population.     

Group predatory behavior by the assassin bugAgriosphodrus dohrniSignoret (Hemiptera: Reduviidae)

Summary Nymphs ofAgriosphodrus dohrni Signoret (Reduviidae) have a strong gregariousness and show group predatory behavior. This study was conducted to clarify adaptive significance of group predation of this species, including laboratory observations and 6-year field surveys. In the laboratory, observations on both solitary and group attacking against armyworms were made at varying prey size classes to compare the capture success rate by solitary predators with that by groups. The efficiency in capturing the prey was significantly higher in group attacking at any prey size class compared. Data obtained from the field surveys indicated the tnedency for searching nymphs to feed in group and to increase the number of predators feeding per prey item with increasing prey size. Average sizes of prey captured were also larger in group feeding throughout the nymphal stage. In particular, it was remarkable that, when prey were “creeping” types, the upper size limit of prey eaten was dramatically increased.     

Extraordinary effects of fertilization status on the reproduction of an arrhenotokous and sub-social spider mite (Acari: Tetranychidae)

Summary Experimental observations on the arrenotokous reproductive patterns of two spider mite species (Acari: Tetranychidae), the long-seta form ofSchizotetranychus celarius (Banks) andTetranychus urticae Koch, revealed that reproduction of unfertilized females of the former is very differnt from that of the latter. Unfertilized females ofS. celarius, which has a subsocial life, laid a few eggs and then became inactive. In contrast, the fecundity of unfertilizedT. urticae females was only slightly reduced as compared with fertilized females. Mother-son matings may thus sometimes occur in naturalS. celarius populations. A two-year field survey revealed that, in the absence of males, overwintering females ofS. celarius occasionally remain unfertilized until early spring. Furthermore, nest foundation observed in late spring indicated that most of the season's first nests were founded by single females. These two sets of observations strongly suggest that motherson mating takes places in nature, corresponding to the reproductive trait seen in the experiment. Mother-son mating inevitably increases the relatedness between nest members. The estimated father's relatedness to its offspring is extraordinarily high under such condition. The possibility that kin-selection in the long seta-form ofS. celarius led to subsociality, especially paternal care, is suggested. This study was supported in part by Grant-in-Aid No. 61540468 from the Ministry of Education, Science and Culture, Japan.     

A new method for describing predator-prey relations in discontinous environments

Summary I propose a new method for anlysing predatorprey interactive systems in discontinuous environments. The basic index used here is a generalized version ofLloyd's (1967) “interspecies mean crowding”, which is defined as the number of individuals of one species existing in a given patch per that of the other species in either the same or different patches at either the same or different times. Four indices are derived from different combinations of the numbers of the prey and the predator in habitat patches. Then, the correlation coefficients between the numbers of individuals in patches in both different locations and times are derived by modifying the above new indices. Using this technique, dynamical changes of the joint distributions of the numbers of predators and prey which reflect variation in local conditions, can readily be described. As an example, this method was applied to an analysis of the outcomes of a multi-patch version of theLotka-Volterra model of predator-prey interactions.     

Systems analysis of an acarine predator-prey system II: Interactions in discontinuous environment

Summary An acarine predator-prey system in a circular stepping-stone environment was described with a simulation model to elucidate the factors responsible for persistence of the system. The main assumptions in this model are: (1) The prey are inevitably eliminated in patches in which predators exist. (2) The density of prey declines and becomes extinct by plant defoliation due to feeding by prey. In this regard this model is different from the models which mimickedHuffaker's (1958) experiments and assumed stable plant-prey relations. Analyses showed that the critical factor in persistence of the predator-prey system was the plant-prey relations, at any combination of other parameters involved in the model. The predator-prey system did not persist long under the unstable relationship of prey and plant. Otherwise the system persisted longer especially when I used a larger number of patches, a larger amount of plant in each patch, and long-distance-migrations of the prey. In particular, frequent emigration of the prey regardless of plant conditions was most effective.     

Anopheles culicifacies giles: Adult ecological parameters measured in rural punjab province, pakistan using capture-mark-release-recapture and dissection methods, with comparative observations onAn. stephensi liston andAn. subpictus grassi

Summary Dispersal, immigration and emigration rates, horizontal and vertical survivorship and absolute population size were estimated for micropopulations ofAn. culicifacies, An. stephensi andAn. subpictus at a series of cattle sheds in rural Punjab Province, Pakistan, during November 1979 and May 1980 using capture-mark-release-recapture and dissection methods. Dispersal was temperature-related, with populations more vagile during May. Mean dispersal distance per individual was low for all species. More than 70% of all recaptures were taken at the point of release and the longest detected flight was 1250 meters. Horizontal survivorship was greater during November and was always less than vertical survivorship calculated from dissection agegrading data. Survivorship during the nulliparous period was greater than survivorship throughout total life, indicating the survivorship curve may be slightly sigmoid. Daily population sizes of endemic and immigrating females and males were calculated usingBailey's (1952) modification of the Lincoln Index, with the daily captures adjusted for immigration which was highest in May. Daily additions to the indoor resting population exclusive of immigrants were estimated using the method ofManly andParr (1968). The relationship of the present findings to malaria transmission and genetic control were discussed.     

Estimation of prey consumption of a mantid,Paratenodera angustipennis (S.) in a natural habitat

Summary Using a relationship between prey consumption and growth rate, field prey consumption of adults ofParatenodera angustipennis (S.) in a paddy field was estimated. Since a great number of grasshoppers (Oxya japonica) lived in the research area and the mantids had frequently eatenO. japonica, we presumed that they consumed onlyO. japonica. As a result, it was estimated that average prey consumptions for 6 days were 406 mg for the females and 23 mg for the males. From the result of this estimation and the feeding rhythm of the mantids, it is concluded that each female captured one grasshopper on average every a few days. By comparing this actual feeding level ofP. angustipennis with those of other predacious arthropods, characteristics ofP. angustipennis as a predator were discussed.     

Biological control of Pacific mites and Willamette mites in San Joaquin Valley vineyards: part III. Role of tydeid mites

Summary In the absence of spider mites, tydeids (Pronematus anconai Baker andPronematus ubiquitus [Mc Gregor]) may serve as alternate prey to maintain good numbers of the predatory mite,Metaseiulus occidentalis (Nesbitt) (Acarina, Phytoseiidae), late in the season. This late-season predator and alternate prey relationship is necessary to stabilize Pacific mite populations and perpetuate balance in San Joaquin Valley vineyards. Thriving laboratory colonies of tydeids were reared on a diet of windblown pollens, including cattail pollen (Typha sp., Typhaceae) and bottlebrush pollen (Melaleuca sp., Myrtaceae).M. occidentalis was successfully reared on a diet of tydeids and ovipositing predator females were obtained. In addition, pollen dusted on grapevines significantly increased both tydeid and indirectlyM. occidentalis populations late in the season. These studies suggest that artificially disseminating cattail pollen or manipulating good pollen producing flora in and around vineyards may be used to correct situations where Pacific mites have become serious pests. This study was supported by grant No. GB-7322 toC. B. Hyffaker by the National Science Foundation.     

Population dynamics of houseflies,Musca domestica, on experimentally accumulated refuse

Summary The population dynamics of the housefly,Musca domestica, on patchy and unstable habitats consisting of refuse was investigated at a waste disposal site by using sticky flypaper and mark-release-recapture technique (Jolly-Seber's method). The newly disposed garbage was favorable for breeding of the flies for about one month after being disposed, while a mixture of garbage and ash from incinerated refuse was less favorable. On the garbage under favorable conditions, the rates of population increase was 1.25–2.82 per day, and approximately 1300–1500 flies were produced per square meter within the available period of one month. The rapid decrease in the fly density was observed just after the appearance of high density peaks. The mark-release-recapture study suggested that this rapid decrease would be mainly due to the density-dependent emigration of adult flies from the patchy habitats. The emigration was also activated when the time after garbage disposition became long.     

Time-specific life tables for the pea aphid,Acyrthosiphon pisum (Harris ), on alfalfa

Summary Time-specific life tables were constructed for three pea aphid,Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), populations using a modification ofHughes' analytical procedure. All populations were studied on second-growth alfalfa (mid-June to mid-July) in south central Wisconsin; data for two populations were collected during 1980, and data for the third population were collected during 1982. The intrinsic rate of increase (r _m) estimated on a physiological time (day-degree) scale under field conditions but in the absence of natural enemies, provided a reliable estimate of potential population growth rate and was used in preference toHughes' approach of estimating potential population growth rates directly from stage structure data. Emigration by adult alatae and fungal disease were the major sources ofA. pisum mortality in each of the three populations studied. These factors were most important because of their impact on reducing birth rates within the local population. Parasitism was never greater than 9 percent. Mortality attributable to predation ranged from 0.0 to about 30.0%; however, even at the highest predator densitiesA. pisum populations increased exponentially.     

Selection for divergent emigration rates in laboratory populations ofMusca domestica

Summary High and low emigration rates through a laboratory system were selected for in populations of house flies (Musca domestica L.). Emigration consisted of movement of flies from on plastic box to another by way of a connecting tube. Selection was carried out by first dividing a wild population of flies into two lines and then selecting for movement from the box in one line and against movement from the box in the other line. The selection experiment was performed twice. In both experiments a statistically significant difference between the two strains was obtained in three to four generations of selection. In the second experiment, after 5 genrations the mean number of high emigration rate flies emigrating in 1 hour was 4.37 times the mean number of low emigration rate flies and in 24 hours was 2.81 times the number of low emigration rate flies. The second experiment was terminated after 6 generations, but the first experiment was continued for 35 generations. In this case, divergence ceased in roughly 15 generations. The possible relevance of the findings to laboratory population experiments in which spatial discontinuities are included is discussed. This study was supported by a research grant of the National Science Foundation (Environmental Biology GB 4567) to Prof. DavidPimentel. The author wishes to thank Prof.Pimentel for his aid and encouragement.     

Population behaviour of the southern green stink bug,Nezara viridula, with special reference to the developmental stages of early-planted paddy

Summary Population behaviour of adults and 5th-instar nymphs ofNezara viridula L. was analysed by means of the marking-and-recapture method in an early-planted paddy field. The field contained five varieties of rice which differend in growth states. It was estimated that a total of more, than 7,000 adults of the first generation, in which at least 3,000 were females, invaded the field from early July to middle August. Egg-mass census data, however, indicated that only 10 per cent or less of the females participated in egg-laying. This was largely due to the, low rate of adult survival. The adults preferred younger plants, for both feeding and oviposition. The method described byIwao et al. (1966) permitted estimate that 3,300–3,400 of the 5 th-instar nymphs and 1,100–1,200 of the adults of the second generation were produced from 298 egg-masses (25, 700 eggs); while 95–6 per cent of the individuals were thought to have died before reaching adulthood. Most of the 5 th-instar nymphs moved less than 4 m in three days as long as the condition of food plants remained suitable, but they tended to move more towards younger plants when those on which they lived became too mature. The apparent survival rate of the second generation adults was very low, probably due both to a rapid emigration and a high mortality of newly-emerged adults.     

Simulation of the interactions of predatoryTyphlodromus mites with the European red mite,Panonychus ulmi (Koch)

Summary Interactions ofTyphlodromus mites and their prey, the European red mite, in orchard settings were examined through computer simulation. In particular, the consequences of very slow dispersal by the predators, compared with the weather-dependent higher rates of prey dispersal, were elucidated. In simulations of the interactions of the predator and its prey, both dispersal and temperature strongly affected the available supply of juvenile prey, and thus could determine whether the predators on an individual tree survived or perished.     

Density-dependent predation of the antLasius niger (Hymenoptera: Formicidae) on two attended aphidsLachnus tropicalis andMyzocallis kuricola (Homoptera: Aphididae)

The antLasius niger was observed collecting honeydew and preying on the two aphid speciesLachnus tropicalis andMyzocallis kuricola on the chestnut treesCastanea crenata. Observation determined how the antL. niger controlled their predation on the aphids in response to the density and honeydew-productivity of the aphids.Lachnus tropicalis was a better honeydew source thanM. kuricola forL. niger in terms of the amount of honeydew collected per unit time by the ants. The number of foraging workers on a tree increased with the number ofL. tropicalis on the tree, but not with the number ofM. kuricola. The density ofL. tropicalis perL. niger worker on a tree had a positive effect on the predation activity ofL. niger on both aphids, whereas the density ofM. kuricola per ant did not have any significant effect. The predation pressure by the ant which increased withL. tropicalis density, however, directed toM. kuricola rather than toL. tropicalis. These facts suggest (1) thatL. niger control their predation activities on aphids with regards to the densities of the attended aphids per worker, and (2) that the ants prey on the aphid species producing less honeydew. The effects of the ant predation on aphids and the importance of these predation effect in antaphids interactions were discussed.     

Evaluation of the role ofMicrovelia douglasi atrolineata (Bergroth) (Heteroptera: Veliidae) as predator of the brown planthopperNilaparvata lugens (St?l) (Homoptera: Delphacidae)

Summary The biology of the veliid bugM. d. atrolineata, its predatory behavior, and the effects of plural hunting were studied to evaluate its role as a predator of the brown planthopperNilaparvata lugens in the Philippines. The probability of planthoppers falling onto the water surface and provision of habitat continuity was measured by a sticky trap placed at the base of rice hills in a greenhouse and in paddy fields. The developmental period of immature stages combined was 21 days. If given prey, females laid 25 eggs on the average during an adult life span of 18 days. Starved adults could survive for only 3–5 days. The functional response to prey density was sigmoid, and the maximum number of prey killed was 7 per day. Prey feeding was completed in 12–36 min. The percentage of successful prey attacks averaged 5–8%, decreasing with higher (and larger) developmental. stages of prey, but adult prey were found the soonest. Plural hunting increased the probability of capturing prey by as much as 2.5 times that by individual hunting. Late-instar nymphs, which may be more active, fell from rice hills in a greenhouse more than early-instar nymphs, and the number falling increased with density. In the field the percentage of planthoppers falling to the water in 1 day varied considerably, from 1% for nymphs in one field to 67% for adults in another field. On the basis of work described above and given the high density of veliid predators in flooded paddy fields of tropical Asia,M. d. atrolineata is considered one of the most important natural enemies of the brown planthopper.