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.     

Resource exploitation of larvae ofGastrophysa atrocyanea Motschulsky andgalerucella vittaticollis Baly (Coleoptera: Chrisomelidae) under a limited resource condition

Summary Resource exploitation by and intraspecific competition in larvae ofGastrophysa atrocyanea andGalerucella vittaticollis were investigated in field and laboratory experiments. Larvae of both species frequently suffered from food shortages in the field. WhenG. atrocyanea larvae suffered from a food shortage, severe intraspecific competition occurred because of lack of predation and parasitism. This exploitive competition was caused by a local food shortage of the host plant. Individuals survived by fast exploitation when food became abundant (contest type competition). TheG. atrocyanea larvae were wasteful of the food resource, and no mechanism by which to economize on the utilization of the resource was acquired because of their exploitation of the abundant resource. In contrast, theG. vittaticollis population probably is regulated by extrinsic factors such as predation and parasitism. Those larvae grew into smaller adults than those ofG. atrocyanea under a food shortage, so that their wasted food consumption was lower than that ofG. atrocyanea. Although intraspecific competition was similar to that forG. atrocyanea, it was not as severe. The food forG. vittaticollis was apt to be appropriated by other wasteful exploitators such asG. atrocyanea, which was superior in resource exploitation; thereforeG. vittaticollis frequently suffered a food shortage. Consequently selection in relation to tolerance to starvation became more acute forG. vittaticollis than forG. atrocyanea, and individuals ofG. vittaticollis that could endure starvation better may have been selected.     

Population dynamics ofTelenomus fariai (Hymenoptera: Scelionidae), a parasite of Chagas' disease vectors IX. Larval competition and population size regulation under laboratory conditions

Summary A series of experiments were carried out with the endophagous egg parasiteTelenomus fariai on its hostTriatoma phyllosoma pallidipennis to determine the possible role of intraspecific competition by the parasite progeny in population regulation of the parasite. Eight parasite densities (1, 3, 5, 10, 20, 30, 40, and 50 individuals per vial) were used, and the design of sequentially sacrificed replicates applied. Survivorship curves for each density indicated smaller number of progeny per host at higher densities, and the shapes of the curves suggested a relatively early mortality process.Morris' linear regression technique for determining within-generation density-dependence was used, and the results showed that only larval mortality could be identified as density dependent. The same technique applied within the larval stage proved that only mortality of larvae in their second, third, and fourth day of development were responsible for population regulation. The applicability of the technique, as well as the relevance of the results for natural population, is discussed.     

More highly female-biased sex ratio in the fig wasp,Blastophaga nipponica Grandi (Agaonidae)

The sex ratio of the pollinator fig wasp,Blastophaga nipponica Grandi (Agaonidae), was examined in an experiment manipulating the number of foundresses. The sex ratio ofB. nipponica was conditional on the number of foundresses and corresponded to the qualitative prediction of the local mate competition (LMC) theory that the proportion of males increases as foundress number increases. However, the sex ratio ofB. nipponica was consistently more female-biased than predicted by extended LMC theories that incorporated effects of inbreeding, and these deviations were statistically significant. Plausible factors that would make predictions more female-biased are discussed.     

Population dynamics of the whitebacked planthopper,Sogatella furcifera (Hemiptera: Delphacidae) with special reference to the relationship between its population growth and the growth stage of rice plants

A population census was conducted to describe the effects of the growth stage of rice on the population dynamics ofS. furcifera, in particular, on immigration, seasonal abundance, population growth rate, and wing-form expression. The number of immigrants was highest on rice plants 17 to 30 days after transplanting (DAT), which suggested that immigrants prefer to settle or remain more on rice plants at the tillering stage (approximately 20–30 DAT). Population growth rate from immigration to the 1st generation decreased with an increase in rice plant age. In contrast, population growth rate from the 1st to 2nd generation was not influenced by rice plant age and was negatively density-dependent. The percentage of macropters (flyers) was positively related to the growth stage of rice when rice was in the vegetative or early part of the reproductive stage, and reached 100% at about 10 days before heading (booting stage). Threafter, most adult females molted into macropters regardless of population density. The roles of host plant age and crowding effect on the population dynamics ofS. furcifera are discussed.     

Contest competition inDrosophila subobscura

The role of larval intraspecific competition in laboratory populations ofDrosophila subobscura was investigated. Mortality is density-independent during the first 3 days after hatching but becomes density dependent as development proceeds to pupation. Although total biomass per patch was independent of initial egg density, competition betweenDrosophila larvae leads to the formation of smaller pupae. This resulted in a population that was dominated by suppressed individuals. Development rate ofD. subobscura larvae was not affected by high larval densities. Smaller pupae give rise to females with fewer eggs in their ovarioles. A simple simulation model, predicting the effects of intraspecific competition on the fecundity of the nextDrosophila generation is described.     

Population dynamics ofMalacosoma neustria testacea (Lepidoptera: Lasiocampidae): Stabilizing process in a field population

Summary Stabilizing mechanism in population ofMalacosoma neustria testacea was investigated in a central part of Japan based on eight year survey. Population fluctuation in each developmental stage in the experimental field was rather small, i.e., 5.9 times in egg and 85.0 times in female adult. Pupal weight negatively correlated with the densities of 5th instar larvae and prepupae (cocoons) and correlation coefficient was highly significant in females. Population density was stabilized by density-dependent dispersal of female moths in preovipositional period. Comparison between fecundity of emerged moths and that of actually oviposited ones in the experimental field suggested that density-dependent dispersal took place as the result of density-dependent size variation, i.e., small-sized female months have higher flying ability. This hypothesis was supported by the experiment in which flying ability of newly emerged female moth was measured. Similar stabilizing mechanism is expected to occur in semelparous or pro-ovigenic insects. Contribution Ser. A, No. 64 from Fruit Tree Research Station, Ministry of Agriculture and Forestry, Japan     

Spatial distribution and mortality process ofAnoplophora malasiaca (Coleoptera: Cerambycidae) eggs in citrus groves

Summary The study was carried out in two (A and B) citrus groves to clarify the spatial distribution patterns of eggs and larvae, and to analyse the mortality process of eggs. From the analysis by using the mean density and the mean crowding, it was clarified that the distributions of eggs were contagious and that larvae were more contagiously distributed than eggs. The τ andz indices showed that the operation of egg mortality was inversely density-dependent in both groves, and that the degree of inverse density-dependence was greater in A than in B grove. The spatial correlations between the emergence holes and the eggs or larvae in each tree, which were analysed by using ω index, showed that the distributions were more overlapping between the emergence holes and the larvae than the eggs. As the result of dividing trees into several groups according to the number of emergence holes, it was clarified that the survival rates of eggs were positively correlated with the number of emergence holes. In conclusion, inversely density-dependent mortality process was considered to be caused by lower mortality rates of eggs in the trees with more emergence holes. Especially in A grove, because the trees with more emergence holes were larger in diameter and more egg oviposition, the inversely density-dependent mortality process was considered to be detected more conspicuously than in B grove.     

The effects of food and density of the movement ofArion ater andAriolimax columbianus (Pulmonata: Stylommatophora) between habitats

Summary Experiments were conducted to determine if slug density, or food quantity and quality could cause dispersal by slugs.Arion ater dispersed quickly from overcrowded areas, where high mortality was incurred by this species. Poor food conditions, caused more dispersal than good food conditions, but food had no effect on the mortality ofA. ater. Neither food nor density factors had significant effects on the dispersal ofAriolimax columbianus. However, moreA. columbianus died in the high- than low-density treatments.A. columbianus mortality was unaffected by the food factor. DispersingArion were heavier than non-dispersers, but there was no difference between the weights of dispersing and non-dispersingAriolimax. There were significant seasonal changes in the dispersal rate, mortality and weight of dispersingArion, whereas only the mortality ofAriolimax changed significantly during the experiments. SinceArion ater did not markedly reduce its activity during unsuitable weather it was able to leave areas of poor food and high slug density fairly rapidly.Ariolimax columbianus' large size allowed it to remain inactive during unfavourable weather and permitted this species to be relatively unresponsive to the experimental treatments.     

Effects of interspecific competition on development and reproduction in two giant water bugs,Diplonychus japonicus vuillefroy andDiplonychus major esaki (Hemiptera: Belostomatidae)

Summary We studied the interpecific competition between 2 species of predatory aquatic bugs,Diplonychus japonicus andD. major by conducting a field experiment. We set up 3 types of experimental plots in the paddy fields whereD. major predominated. The two plots contained single species of eitherD. japonicus orD. major, respectively, and one plot had both species in equal number. We compared the development and the reproductive performance between plots in each species. InD. japonicus, the number of eggs and early instar nymphs were significantly smaller in the plots containing both species than in the monospecific plots. However, the numbers of late instar nymphs and newly emerged adults were not significantly different between plots. The proportions of starved nymphs in both plots were larger than those in theD. japonicus's natural habitats. The final densities of adults in both plots were lower than those in the natural habitats. These results suggest that lower density ofD. japonicus in these paddy fields is due to the lack of available food for nymphs rather than the effects of interspecific competition withD. major. InD. major, significant differences were not found in the number of eggs, each instar nymphs and adults. These results suggest that the effects of interspecific competition did not affect the reproductive performance ofD. major.     

A granulosis virus, possible biological agent for control ofAdoxophyes orana (Lepidoptera: Tortricidae) in apple orchards

Summary Based on the results of ecological surveys ofAdoxophyes orana and its natural enemies in apple orchards sprayed with the granulosis virus and control plots, we constructed working models to simulate the population dynamics in three different experimental plots; those treated with chemical insecticides, those with granulosis virus, and controls. The number of individuals killed by predators, parasitoids and by miscellaneous mortality factors could be calculated on the assumption of imperfect density relations; that is, relation of the number killed by each factor with the initial number of larvae was represented by a curve with an upper asymptote. We could estimate the proportion of virus infection using curves with upper asymptotes. Rate of increase from pupa to middle instar larvae of the next generation was subject to strong density-effect. Simulation we proposed in this paper suggests a possibility that a single spray of the virus at 1st generation can reduce not only the number ofA. orana larvae in the 2nd and 3rd generations but also the degree of fruits injured by this insect. Spray of chemical insecticide is considered to be ineffective in reducing the pest density and the degree of injury to low levels in subsequent generations, as compared with untreated plot, where the density of the 1st generation larvae is low.     

Estimatingdendroctonus frontalis (Coleoptera: Scolytidae) daily infestation dynamics

Mathematical procedures are given to estimate infestation totals and daily life stage arrivals, departures, and mortality ofDendroctonus frontalis Zimmermann for an infested tree in the field. These estimates are based on minimal sample data and are designed to utilize all available information. Daily arrival estimates for larvae, pupae, and callow adults are obtained by indirect analysis without direct observation of these stages. The procedures are applied to 147 infested trees, and the results are transformed to a common time basis to obtain daily expectations by life stage for an “average” tree. These expectations suggest optimal times for field sampling or relative times of sampling when optimal times are missed. Expected daily arrival distributions by life stage for a single egg and a single attacking adult are given. Procedures are given for utilizing collateral information to obtain an infestation total and daily arrival estimates for a boundary life stage. The results of this study are applicable to anyD. frontalis field study, and the procedures given are applicable to any bark inhabiting insect having similar habits.     

Population studies ofBrevicoryne brassicae (L.), its parasites and hyperparasites in England

Summary Studies on populations ofBrevicoryne brassicae (L.), its parasites and hyperparasites were carried out by actual counting in the sprouts field and by sticky and water traps.B. brassicae was found to be attacked by one primary parasite,Diaretiella rapae (McIntosh), which in turn is parasitized byAlloxysta brassicae (Ashm.),Asaphes vulgaris Walker,A. suspensus (Nees),Pachyneuron minutissimum (F?rster) andDendrocerus carpenterii (Curtis). The aphid population in the field was started by immigrant alates which were found flying too early to be synchronized with the sprouts plants. SimilarlyD. rapae was not synchronized with the aphids although many individuals could have been carried into a plot through parasitized immigrant alates, of which less than 30% were found parasitized. Because of high hyperparasitism (especially byA. brassicae)D. rapae was not able to maintain a high rate of parasitism to curb the aphid population growth. The maximum percentage mummies being 27.8%, while the maximum, percentage parasitism being 56.6% recorded only during the early 1974 season (mean=12.9%). The decline of aphid population from September onwards was largely due to the cold weather, Syrphid predation and occasionally fungal attack. The high rate of hyperparasitism byA. brassicae is attributed to its better synchronization withD. rapae. The mean percentage of parasite that emerged from mummies collected during 1973–74 wereD. rapae 31.3%,A. brassicae 64.3%,A. vulgaris andA. suspensus 4.3%,D. carpenterii 0.2% andP. minutissimum 0.1%.     

Differences in egg wastage by superparasitism, contrastingVenturia (=Nemeritis) canescens searching singly versus searching in groups

Summary A statistical and graphic study is presented of the wastage of eggs byVenturia (=Nemeritis) canescens when searching singly and in groups of 10 among hosts at four different host densities in laboratory universes as described byHuffaker andMatsumoto (preceding paper of this journal). The host insect was the fluour mothAnagasta kühniella and the host densities used were 10, 30, 100 and 200 per universe. Intensity of egg wastage due to superparasitim varied significantly according to host density, and between the two parasite densities employed, 1 and 10, using bothF-tests and chi-square tests. Plots ofk-factor analysis on this egg wastage showed high negative correlations with host density, and the raw data for single parasites was well represented by a parabola while that for the grouped parasites departed from this relationship only at the lowest host density. These studies were conducted as a part of a general investigation into the processes operating in the population dynamics of arthropods under grants from the National Institutes of Health, U. S. Public Health Service (#A10-1611), and the National Science Foundation and Environmental Protection Agency (NSF DEB7504223) to the University of California. The findings, opinions and recommendations expressed herein are those of the authors and not necessarily those of the University of California, the National Institutes of Health, the National Science Foundation or the Environmental Protection Agency.     

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.     

Inconstancy of Taylor'sb: Simulated sampling with different quadrat sizes and spatial distributions

Summary Taylor's power law,s ² =am ^b , provides a precise summary of the relationship between sample variance (s ² ) and sample mean (m) for many organisms. The coefficientb has been interpreted as an index of aggregation, with a characteristic value for a given species in a particular environment, and has been thought to be independent of the sample unit. Simulation studies were conducted that demonstrate that the value ofb may vary with the size of the sample unit in quadrat sampling, and this relationship, in turn, depends on the underlying spatial distribution of the population. For example, simulated populations with hierarchical aggregation on a large scale produced values ofb that increased with the size of the sample unit. In contrast, for a simulated population with randomly distributed clusters of individuals, the value ofb eventually decreased with increasing quadrat size, as sample counts became more uniform. A single value ofTaylor'sb, determined with a particular sample unit, provides neither a fixed index of aggregation nor a complete picture of a species' spatial distribution. Rather, it describes a consistent relationship between sample variance and sample mean over a range of densities, on a spatial scale related to the size of the sample unit. This relationship may reflect, but not uniquely define, density-dependent population and behavioral processes governing the spatial distribution of the organism. Interpretation ofTaylor'sb for a particular organism should be qualified by reference to the sample unit, and comparisons should not be made between cases in which different sample units were used. Whenever possible, a range of sample units should be used to provide information about the pattern of distribution of a population on various spatial scales.     

Analysis of contagiousness in the action of mortality factors on the western tent caterpillar population by using the \mathop m* - m\mathop m\limits^* - m relationshiprelationship

Summary The contagiousness in the operation of mortality processes on the colonies of the western tent caterpillar,Malacosoma californicum pluviale, was analyzed from two different aspects: successive changes in the frequency distribution of the number of surviving individuals per colony in the course of development, and the distribution pattern of the individuals killed by some biotic mortality factors. Also, for a tachinid parasite,Tachinomyia similis, the analysis was made on the egg-laying pattern on colonies as well as on individual larvae. The methods of these analyses were all based on the relation of mean crowding (m) on mean . A braconid parasite,Rogas sp., tended to kill few individuals together once it attacked a colony, but its effect on host colonies was rather equivalent to the random removal of individuals from all the colonies. Diseases in the late-stage larvae before cocooning was contagious in their action. Nuclear polyhedrosis virus seemed to have no basic contagiousness in its action, but it caused highly contagious distribution of deaths among the colonies when its average incidence was high. A spore-formingBacillus had a tendency to kill several individuals once it appeared in a colony, but the distribution of its incidence (no. of times it appeared per colony) was considered to be nearly at random. The female ofTachinomyia tended to lay more than one egg successively on the same colony. It also attacked individual larvae with a definite tendency for aggregation, which seemed to be resulted from the parasite’s preference to large hosts. When the number of eggs laid on prefered hosts exceeded a certain threshold, however, the fly seemed to change its attention to less attractive, smaller individuals.     

Contest and scramble competitions in two bruchid species,Callosobruchus analis andC. Phaseoli (Coleoptera: Bruchidae)

Summary We performed multiple-generation competition experiments betweenCallosobruchus analis andC. phaseoli with different bean sizes. In each system, we supplied 5 g of mung beans (Vigna radiata) every 10 days. We examined three types of bean conditions: 5 g of large beans, 5 g of small beans, and a mixture of 2.5 g of large and small beans. In small bean condition,C. analis dominatedC. phaseoli in all three replicates andC. phaseoli was extinct by the 260th day. On the contrary,C. phaseoli overcameC. analis within 250 days in large beans in all three replicates. In mixed beans condition the two bruchid species coexisted more than 500 days in two out of the three replicates. Even in the exceptional case, both species coexisted for 460 days. These results were examined in the light of the predictions from short-term larval competition experiments and a game theoretical model by Smith and Lessells (1985). The density and frequency dependent results during larval competition inside a bean was concluded to be a main factor to produce the above long-term competition results.     

Analysis and simulation modelling of population dynamics and bioenergetics ofCryptolestes ferrugineus (Coleoptera: Cucujidae) in stored wheat

Summary The consequences of infestation of stored wheat by the rusty grain beetle,Cryptolestes ferrugineus (Stephens) was determined for 222 d at 30°C in 70-1 drums containing wheat at 13.5% moisture content. Temperature, grain moisture, seed damage, germination and weight, dust weight, fat acidity values (FAV), published data on growth, reproduction, survival and cannibalism rates and energy budget were used to develop a computer simulation model to simulate the population dynamics ofC. ferrugineus at 30°C. In the insect-free control system, the fungi,Alternaria alternata decreased,Aspergillus glaucus group andPenicillium spp. increased, probably causing a rise in FAV of the grain. In the insect-infested system,C. ferrugineus could only eat the wheat germ of kernels that had a broken bran layer; 35.7% of the wheat germ or 914.6 J per 100 kernels was consumed. Within two generations after initial introduction,C. ferrugineus reached a peak in numbers and biomass polluting the ecosystem with excreta and remains, and accelerating the deteriorative process observed in the insect-free control system by increasing respiration temperature, FAV and reducing grain germination. After 87 d, the insect population declined to low levels. The simulation model provided a close match between the observed and predicted numbers of insect life stages and bioenergetic variables during the insect population growth phase. Simulation trials suggested that cannibalism of larger compared with smaller immature stages would be more wasteful of developmental time and energy, reducing the number of individuals reaching reproductive age, and that density-dependent fecundity was probably not an important regulatory mechanism ofC. ferrugineus population dynamics in this study. Contribution No. 1314 from Agriculture Canada Research Station, Winnipeg, Manitoba, R3T 2M9, Canada