Some beneficial effects of aggregation in young larvae ofPryeria sinica moore (Lepidoptera: Zygaenidae)

Summary The effects of group size on the survival and development of young larvae ofPryeria sinica Moore were investigated by laboratory and field experiments. Under laboratory conditions, about 20% of isolated larvae died of unsuccessful feeding in the first instar, however, larvae survived successfully in aggregations of four or more individuals. In the field, larvae emerge in early spring and wait for new leaves to open before feeding. In this period, the larger the group size of hatchlings the survival rate became higher. The nest-web spun by hatchlings was considered to play an important role in protecting them from desiccation. In the period that larvae began to feed on leaves, more than 36 larvae are necessary to aggregate for the successful establishment of feeding groups. The nest-web played an important role also in the establishment of feeding group. However, the natural group size of the first instar larvae was larger than the minimum group size to spin a sound nest-web in the field experiment. On the other hand, in later stage, larvae in a large group did not have an excess advantage in survival or developmental rate over larvae in a small group. It was found that the experiments on survival and developmental rates could not explain the reason that this species maintain large compact groups in the most part of larval period. The study was partially granted by the Ministry of Education (No. 374205).     

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.     

Tables for the analysis of selective predation experiments

Summary This paper discusses the analysis of selective predation experiments with two types of prey when the prey are not replaced after they have been removed by the predators. In an earlier paper (Manly et al., 1972) consideration was given to situations where the replication of experiments allows the estimation of standard errors from the experimental results; in the present paper a table of standard errors is given for a large range of experiments and replication is therefore no longer necessary. The standard errors were calculated on an electronic computer by solving the exact equations given in the earlier paper. The suggested method of analysis is illustrated using some data where the prey were red and yellow artificial ‘maggots’ and the predators were garden birds.     

Studies on the basic components of the predation ofPhytoseiulus persimilis Athias-Henriot (Acarina: Phytoseiidae)

Summary The basic components of the predation ofPhytoseiulus persimilis Athias-Henriot feeding upon eggs ofTetranychus urticae Koch were studied in an open system where the predator could disperse freely. The type of the functional response of the predator to the density of its prey was the same as that studied so far in a closed system, i.e.,Holling's Type 2. The search rate of the predator, however, was much lower in comparison with the result from a closed system. The oviposition of the predator per day was only weakly related to prey densities higher than 10 per leaf disc. But the emigration rate was inversely dependent upon the initial prey density up to 60 per leaf disc. The searching behaviour of the predator was influenced by both the web density spun byT. urticae and the density of the prey: the predator searched for its prey intensively only after it had contact with web. Mutual interference was observed in prey consumption, but not in the emigration rate. The emigration rate was largely dependent upon the prey density available per predator.     

An analysis of the predator-prey system in the paddy field

Summary A predator-prey system involvingLycosa pseudoannulata as predators and both the green rice leafhopper,Nephotettix cincticeps and the brown planthopper,Nilaparvata lugens as prey was studied in an experimental paddy field. Daily predation rates on the prey and weekly disappearance rates ofLycosa females were related to densities of both predators and prey by multiple regression. During the off-season of reproduction for predators and prey, it proved possible to simulate the interaction betweenLycosa and its prey.     

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.     

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.     

Prey preference of the wolf spider,Pardosa pseudoannulata (Boesenberg et Strand)

Summary Functional responses of the wolf spider,Pardosa pseudoannulata (Boesenberg et Strand) attacking the rice brown planthopper,Nilaparvata lugens (St?l.), and the mirid predatorCyrtorhinus lividipennis Reuter were both those of Holling Type II. The attack rate was higher and handling time lower forC. lividipennis. However, when caged with the two prey, the wolf spider showed a significant preference forN. lugens at a lower prey proportion. Proportions of prey attacked were significantly different from the expected ratios of prey available as well as from the predicted preferences derived from the functional response parameters. As proportions ofN. lugens attacked changed from greater to less than expected as the proportions ofN. lugens available increased, a “reverse switch” behaviour seems to be evident.     

Social structure and the defensive role of soldiers in a eusocial bamboo aphid,Pseudoregma bambucicola (Homoptera: Aphididae): A test of the defence-optimization hypothesis

A complete understanding of the evolution of sociality in aphids requires a detailed knowledge of the patterns of soldier investment in their ecology. The eusocial bamboo aphidPseudoregma bambucicola has a morphologically specialized first-instar soldier caste. The proportion of soldiers was positively correlated with colony size. Within a colony, soldiers were evenly distributed among subcolonies; within each subcolony, however, their distribution was biased toward peripheries which were exposed to many predators. Field experiments introducing natural enemies such asEupeodes confrater (Diptera: Syrphidae) andSynonycha grandis (Coleoptera: Coccinellidae) revealed that the survival rate of these predators was negatively correlated with the density of soldiers, suggesting that soldiers can more or less defend their colonies by killing or removing a range of natural enemies. Observations suggest that large mature colonies attract more predators than newly established small colonies and that, within a colony, the predators attack each subcolony regardless of its position on bamboo shoots. This implies the presence of a positive correlation between colony size and predation risk. Thus, the investment in soldiers seems to reflect the attacking pattern of predators within a colony. These results agree with the defence-optimization hypothesis in soldier investment ofP. bambucicola colonies.     

Elimination ofSitotroga cerealella (Olivier) bySitophilus zeamais Motschulsky from mixed laboratory cultures on maize

Summary This paper describes a series of experiments conducted to determine whySitophilus zeamais Mots. andSitotroga cerealella (Oliv.) could not survive together in maize cultures in the laboratory. The effect ofS. zeamais on different developmental stages ofS. cerealella was investigated. The presence of adultS. zeamais slightly affected moth copulation, egg laying and moth eggs in a mixed culture, but large numbers of developing moths inside maize grains were killed by the adult weevil through feeding on the grains. The major cause of elimination ofS. cerealella byS. zeamais from mixed cultures was therefore found to be damage to the immature moths in grain and such moth mortality increased as the developing moths became bigger in the grains. A weevil: grain ratio of approximately 1.4∶1 was found to be the critical weevil density at which the moth disappeared from the mixed cultures.     

Comparison of life tables between the solitary eumenid waspAnterhynchium flavomarginatum and the subsocial eumenid waspOrancistrocerus drewseni to evaluate the adaptive significance of maternal care

Summary I compared life tables between the solitary eumenid waspAnterhynchium flavomarginatum Smith and the subsocial eumenid waspOrancistrocerus drewseni Saussure in Kyoto, Japan, during 1980–1983. The subsocial eumenid is parthenogenetic in this study area. There were 9 identified mortality factors in the solitary eumenid and 7 in the subsocial eumenid, 6 of which were common to the two eumenids. The important differences of mortality between the two eumenids were seen in the egg, larval, and prepupal stages. In the egg stage, mortality by the phorid flyMegaselia sp. was much lower in the subsocial eumenid (1.4%) than in the solitary eumenid (15.0%) likely because of the matenal care of the subsocial eumenid (progressive provisioning and other related behavior), which reduced predation pressure. In the larval stage, mortality by the miltogrammine flyAmobia distorta was also lower in the subsocial eumenid (8.1%) than in the solitary eumenid (23.8%) also probably because of the maternal care of the subsocial eumenid. A comparison of mortality in the two eumenids between the stable, long continuing natural nest sites and the additional temporal ones showed that the phorid fly remained near its birth place and parasitized stable nest sites. The miltogrammine fly followed returning eumenid wasps and parasitized those nest sites that have a high host density. In the prepupal stage, mortality by endogenous death was higher in the subsocial eumenid than in the solitary eumenid. Mortality due to the rhipiphorid beetle was also higher in the subsocial eumenid probably due to more frequent flower-visits by the subsocial eumenid. The defense mechanism of the subsocial eumenid was discussed in relation to the evolution of subsociality. Contribution to the ecological studies of the eumenid wasps. I.     

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.     

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.     

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.     

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.     

Anopheles subpictus Grassi: Observations on survivorship and population size using mark-release-recapture and dissection methods

Summary A mark-release-recapture experiment to estimate population survivorship and absolute size was performed with wild-caughtAn. subpictus adults at the village of Khano-Harni, Lahore District, Punjab Province, Pakistan during September 1978, the end of the monsoon rainy season, when temporal population abundance was maximized. Daily survival rate estimated from the recapture sequence of marked adults was low, males=0.192 and females=0.343. Survivorship for females estimated by several vertical age-grading procedures ranged from 0.347 to 0.628. Both stage- and age-specific life tables were calculated from vertical age-grading data determined by the dilatation method. Female and male population size was estimated byBailey’s modification of theLincoln Index and was found to average 4478.4 and 6106.8, respectively. The bionomics, survivorship and population size ofAn. subpictus in the Lahore are indicated that this species was probably not important in the transmission of human malaria.     

Genetic control ofHylemya antiqua III. Differences in pupation ability between two strains

Summary Some relevant traits of a wild (L) and a laboratory (C) strain ofHylemya antiqua (Meigen), determining differences in their pupation ability under experimental conditions have been investigated in relation to genetic control. The wild strain showed an intrinsic higher pupation ability than the laboratory strain. The minimum feeding period was 0.6 days longer for the C strain. The minimum larval dry weight was different for the two strains. With a normal feeding period C larvae pupated on average 1.63 days later than L larvae. By the shortening of the larval feeding period an acceleration of the larval development of both strains was observed: the acceleration of development was more marked for the wild strain. This result has been contrasted with published works onDrosphila. The consequences of these differences as far as the competitive ability of each strain is concerned, have been discussed in relation to genetic control.     

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.     

A life table ofMogannia iwasakii (Homoptera: Cicadiidae) in sugarcane field of Okinawa

Summary A preliminary life table of the sugarcane cicada,Mogannia iwasakii, which became a pest of sugarcane in Okinawa recently, was presented based on the results of field survey. Mortality rates during egg and later nymphal stages were low but a remarkable reduction of the number of individuals in a cohort took place at the 1st nymphal instar, mainly due to predation by ants. Ants also killed the cicada during and just after the final ecdysis and birds concentrated their feeding on adults. Prenatal mortality of adults was, however, low in the infested area, suggesting the ‘escape’ of cicadas from the pressure of predators. This espace is considered to be a factor responsible to the maintainance of outbreak for a long time. Increase in the acreage of ratton canes and wide-use of organochlorine insecticides during the 1960’s were assumed to be the factors responsible to the initial increase of this species.