Larval Population Density Research Articles

Yield Loss Caused by Heterodera avenae in Cereal Crops Grown in a Mediterranean Climate1

In south‐eastern Australia, where large areas of cereal crops are grown in a Mediterranean climate, yield loss caused by Heterodera avenae is generally more severe than in Northern Europe. This appears to be due to differences in seasonal cropping patterns and the stages of crop growth when roots are exposed to larvae. Field observations and laboratory experiments show that, in Australia, crops ≪ sown early ≫, in late autumn, are less damaged than those ≪ sown late ≫. This is explained by the times of emergence and population density of larvae, by the nematode‐fungus interaction and by the environmental conditions affecting plant growth, rather than by differences in the nematode or in host tolerance.

Alfalfa Weevil Larvae Control, Kentucky 1981

Abstract The test area was a 3-yr-old stand of Buffalo variety alfalfa. The plots were 34 ft x 36 ft and each treatment and the untreated control were replicated 3 times in a completely random design. Twenty gal of spray was applied per acre. Treatments were applied with a low-pressure, low-volume, Hahn field sprayer equipped with 21 Spraying systems 8003 Teejet nozzles and operated at a pressure of 35 psi. Population densities of larvae were determined 3, 6, 13, 17, and 22 days following treatment by collecting 10 sweeps from each plot with a standard 15 inch dia net. A damage rating was based, on a scale of 1-9 where 1 = no damage and 9 = 100% of leaves consumed, with 2-8 being intermediate. Treatments were applied Apr 21.

Comparison of early and late timing of spray applications for control of spruce budworm in Quebec

An experiment was conducted in the Lower St. Lawrence region of Quebec in 1978 to determine (1) the validity of aerial spray applications of aminocarb timed against emerging L2 larvae of the spruce budworm (Choristoneurafumiferana (Clem.)) as well as (2) the relationship of timing spray applications and success of treatment. Two successive applications timed at peak L4–L5 (regime C) gave better results than similar treatment at peak L2 and peak L4 (regime A). Reduction in larval population density, and the amount of foliage saved due to regime C were almost twice that obtained with regime A.

Life history and distribution ofAdoryphorus couloniBurmeister (Coleoptera: Scarabaeidae) in Canterbury, New Zealand

Abstract The life history and distribution of an introduced population of Adoryphorus couloni Burmeister in the Port Hills of Canterbury is described. The life cycle is of 2 years' duration. Eggs are laid in October-November and hatch after 5–6 weeks. Larvae reach the third stage in February–March and remain in this stage until pupation in January–February of the following year. Adults eclose in March and develop the full oocyte complement in April, but do not emerge above ground, fly, or mate until September. No food was found in the gut of adults at any time. Larval population density reached 250 per m2, but no pasture damage was observed.

Seasonal variation in the population density of larvae of Boophilus microplus (Canestrini) (Acari: Ixodoidea) in Jamaican pastures

AbstractA study was made of the seasonal variation in population density of larvae of Boophilus microplus (Can.) in four locations in Jamaican pastures where the mean annual precipitation ranged from 59 to 222 cm. Variations in population density were related to rainfall. Generally, four months of heavy rains in August to November preceded significant increases in B. microplus populations in December to February. This was followed by a reduction then another slight increase, resulting in a bimodal pattern of activity. Although populations fell to very low levels by the end of the dry season, only in one focus were they depleted to undetectable levels.

1977年筑後におけるコブノメイガの発生消長

The population densities of larvae and adults of the rice leaf roller, Cnaphalocrocis medinalis GUENEE, were investigated by a direct observation in the experimental paddy fields at Chikugo, northern Kyushu. In the field of early-planting culture, young instar larvae began to appear at the end of June and the larval density of the 4th and 5th instars reached 0.75 per hill in early July. Thereafter, the density was very low level until harvest. In the field of normal season culture, the larvae were observed from mid-July and their population densities of the 4th and 5th instars increased gradually, reach-ing a maximum of 0.23 per hill at the end of August. The larval density decreased gradually from early September and only a few larvae were found just before harvest, early November. It seemed that the generations overlapped each other later than August, since various instars of the larvae were observed in a field at the same time. There were distinct peaks of adults occurrence : one peak in early-planting culture in mid-July and two in normal season culture in early August and late September. Two hymenopterous parasites were observed infesting larvae of the pest. The highest percentage parasitism of Trathala flavo-orbitalis was 30.3 % in early-planting culture in early July, while that of Apanteles sp. was 12.5 % in normal season culture at the end of August.

LONG TERM STUDY OF THE EFFECTIVENESS OF AERIAL APPLICATION OF BACILLUS THURINGIENSIS – ACEPHATE COMBINATIONS AGAINST THE SPRUCE BUDWORM, CHORISTONEURA FUMIFERANA (LEPIDOPTERA: TORTRICIDAE)

AbstractBacillus thuringiensis (Dipel® 36B) mixed with a sublethal concentration of acephate (Orthene®) (O, S-dimethyl acetylphosphoramidothioate), an organophosphorous insecticide, was applied at 2.35–14 l./ha to white spruce (Picea glauca) and balsam fir (Abies balsamea) trees infested with spruce budworm, Choristoneura fumiferana (Clem.). The treatment rate was 20 Billion International Units of B. thuringiensis (B.t.) activity with or without 42 g of active ingredient of acephate/ha.The ground deposit of the standard Dipel wettable powder formulation was 12% of emitted volume compared with 21–32% for the Dipel 36B flowable. The viability of B.t. spores was drastically reduced after 1 day of weathering but a high level of biological activity by the spore–crystal complex persisted for up to 20 days post-spray due probably to crystal activity.The addition of about 10% of the recommended operational rate of acephate to the B.t. suspension increased larval mortality by 34% when applied at 4.7 l./ha. Reductions in budworm populations were 97–99% in B.t. + acephate plots and 86–90% in B.t. alone plots.Plots with moderate budworm densities of up to 27 larvae/100 buds on white spruce and 36/100 on balsam fir were satisfactorily protected from excessive defoliation in the year of spray by B.t. with or without acephate. Plots with higher population densities were not satisfactorily protected based on the branch sample examination but aerial color photographs indicated good protection to the top third of the trees. Population declines were greater and defoliation and oviposition were lower in the treated plots than in the untreated checks 1 year later without further treatment. Two years later the larval population densities in all plots were low but the density was twice as high in the untreated check as in the treated plots, indicating long term suppression by the treatments. Defoliation was negligible in all plots.The treatments had no deleterious effect on spruce budworm parasitism. The data indicate that the integrated approach using Bacillus thuringiensis – chemical pesticide combinations is a viable alternative to the use of chemical pesticides alone in spruce budworm control. Large scale testing is now warranted.

Expression of autogeny in relation to larval population density of Sarcophaga bullata Parker (Diptera: Sarcophagidae)

The expression of autogeny in S. bullata was influenced by the larval rearing conditions. Low larval population densities resulted in large flies that were autogenous. On the other hand, high larval population densities produced small flies that were anautogenous, In anautogenous females the size and stage to which the follicles developed varied with the size of the fly. When reared on a sucrose–water diet, the females from an intermediate larval population density possessed larvae, mature eggs, degenerate follicles, or undeveloped follicles.

Ecological studies on chironomids in Lake Suwa : I. Population dynamics of two large chironomids, Chironomus plumosus L. and Spaniotoma akamusi Tokunaga.

Population dynamics of two large chironomids, Chironomus plumosus and Spaniotoma akamusi in Lake Suwa were studied through a four-year period from 1967 to 1970. 1. Based on the daily catches of midge by means of light trap, three emergence periods in a year were confirmed in C. plumosus (April-May, June-July and August-October) and only one in S. akamusi (October-November). 2. C. plumosus produces three generations yearly in the littoral region. In the profundal region, however, it usually lacks the second generation and some part of the larvae of the first generation emerges finally in the third emergence period. 3. Larvae of S. akamusi disappeared from the surface layer of mud bottom in May as the result of their burrowing. Pupation and emergence took place after their reppearance at the surface layer in September. 4. In the imagines of C. plumosus trapped through an emergence period, males as a rule predominated over females (males 50-83%). The predominance of males over females was even more striking expressed in S. akamusi (males 83-93%). 5. Population density of larvae of C. plumosus attained its maximum in June (ca. 1200-5400 individuals/m2 in the profundal region) and in October (ca. 1500 to 2100/m2 in the same region) with the appearance of newly hatched larvae in the lake bottom. The maximum of biomass appeared either in correspondence to that of population density or a little later, and reached 15-90 and 10-27 g fresh weight/m2 in the above-mentioned periods respectively. 6. Population density of larvae of S. akamusi reached a maximum (ca. 700 to 4800 individuals/m2 in the profundal region) in the period from December to March. The maximum biomass was found in March (ca. 10-96 g fresh wt./m2) when the growth of the larvae had been almost completed. 7. Survival rate of wintered larvae of C. plumosus was very low (ca. 6-7%) in 1968 and 1969, whereas it amounted to about 70% in 1970, followed by an unusually intensive emergence. 8. The quantity of pupae produced in an emergence period was estimated based on the numbers of larvae before and after emergence. The total amount of pupae produced per year was estimated at ca. 268-354 tons in C. plumosus and at ca. 10-168 tons in S. akamusi for the whole lake. A certain quantitative relationship was found between the total number of trapped imagines and the estimated number of pupae produced in an emergence period in both species.

Recent Advances in Insect Population Dynamics

A field study concerning insect abundance begins with the identification of the insects concerned and with a study of their life cycles and natural history. It then progresses to the taking of census counts from which life tables can be derived, as discussed by Harcourt in the last volume of An­ nual Review of Entomology. We wish first to examine the next two stages in the study, the analysis of life tables and the development of population models, and to discuss their properties; second, to stimulate workers to de­ fine more precisely their reasons for collecting census figures and help them develop a critical understanding of the analytical methods they apply to them, particularly as there are already in the literature examples of the in­ correct use of analytical methods and of their application to unsuitable data. Census routines must be carefully planned to provide information of sufficient accuracy about all the important factors concerned. Provisional analyses should be used early in the study so that serious gaps are revealed; then, census methods can be improved as soon as possible. Many studies in­ clude some routine measurement of weather factors, but if these figures are thought to be important this should be confirmed by physiological studies. If parasites are thought to be important, then a life table must be prepared for them; this will require, as a minimum, separate counts of the parasite's adult and larval popUlation densities in each generation. If predators are thought to be important, their numbers, food requirements and population' regulation also must be investigated.

A population study on larvae of the damselfly Pyrrhosoma nymphula (Sulzer) (Odonata: Zygoptera)

1. Data on population density, mortality rates and seasonal changes in distribution in larvae of the damselflyPyrrhosoma nymphula (Sulzer) (Odonata: Zygoptera) are described. Field work was carried out between July 1966 and July 1968 in a small weedy pond near to Durham City. 2. Samples were taken using a standard net sweep, and converted to numbers per m2 using a conversion factor. 3. Larvae made pronounced movements during development, one consequence of which was the virtual complete separation of senior and junior age-classes into different areas of the pond throughout development. This may have been important in preventing predation by large larvae on smaller individuals. 4. Mortality rates were constant within year-classes but varied between year-classes, being 99.5, 78 and between 60 and 70 percent per annum in the 1965, 1966 and 1967 year-classes respectively. 5. Larval population densities varied markedly between year-classes. Thus, there were approximately 340 and 110 newly hatched larvae per m2 in July 1966 and 1967 respectively, and 2 and 23 final instars per m2 prior to emergence in May 1967 and 1968 respectively. 6. An independent check on the population data was possible at emergence. Complete collections of exuvia yielded estimates of the number of larvae emerging from the pond that were 24 percent more in 1967 and 34 percent less in 1968 than the calculated number of larvae present prior to emergence.

Tabanid1 Larval Habitats and Population Densities in an Alluvial Area in Southern Louisiana

Study of tabanid larval habitats generally has been confined to swampy areas, streams, ponds, marshes, and other areas in which a high soil moisture content prevails. The work of Logothetis and Schwardt (1948), Tashiro and Schwardt (1949, 1953), Schomberg (1952), and Schomberg and Howell (1955) are notable exceptions.

Respiration in Drosophila—III influence of preimaginal environment on respiration and ageing in Drosophila melanogaster hybrids

Rate of oxygen consumption, daily, mean and total fecundity, fertility and adult life span of Drosophila melanogaster imagos were measured, at 25°C, from emergence up to death. Reciprocal hybrids, from the cross between two highly inbred lines, Gabarros 4 and Abeele, produced at preimaginal densities of 30 and 240 eggs per standard tube of 5·7 cm 2 of surface, were used. The respiration measurements were carried out according to the technique of Gregg and Lints; all the measurements were realized on individual females; age, size and weight were taken into account. Increase of the preimaginal eggs (and larvae) density reduces the size of the emerging adults, prolongs the duration of development and lengthens the adult life span; the total fecundity do not appear to vary considerably; the mean fecundity, however, is much smaller, the egg-laying period is prolonged and the maximal daily egg production is attained later. Between emergence and death the two reciprocal hybrids have almost identical mean respiration rates at both the population (eggs and larvae) densities studied. Respiration rate decreases with age in both hybrids when larval population density is 30 eggs per tube. There is no relation between respiration rate and age for either hybrid at population density of 240 eggs per tube. No relation emerges between rate of oxygen consumption and the other quantitative traits measured when all four genotype-environment combinations are considered together. Specifically the observations do not reveal any correlation between mean rate of oxygen consumption and mean daily egg-production, or between mean rate of oxygen consumption and life span. The results are discussed in relation with different ageing and respiratory control theories.

Abundance and Microdistribution of Larval Chironomidae in Stabilizaton Lagoons1, 2

Two different population structures of larval Chironomidae present in a 3-celled vs. a 1 cell 1 stabilization lagoon were studied from 1964 to 1966 in Oregon. Statistical analysis of dredging results from the 3-celled lagoon showed that total larval abundance was greater in winter, greater in the primary cell, and consistently greater in peripheral zones. Significant differences in larval population densities showed the following order of abundance: Glyptotendipes barbipes (Staeger) > Chironumus riparius Meigen > Anatopynia dyari (Coquillett). The established order of abundance resulted from greater tolerance on the part of G. barbipes than either C. riparius or A. dyari for physicochemical stress. Moreover larval A. dyari required more space for growth and development than did the tube-dwelling species. Dredging data from the 1-cell lagoon showed that total larval abundance was greater in the summer, greater for G. barbipes than for A. dyari, and greater for G. barbipes in both peripheral and central zones. The absence of C.riparius populations resulted from sustained sewage loading. The main factors affecting midge populations in both lagoons are considered to be: sewage influent quality and quantity, depth of water, degree of peripheral slope, and availability of dissolved oxygen at the soil-water interface.

The Effects of Some Soil-Borne Fungi On the Sex Ratio of Heterodera Rostochiensis On Tomato

The sex ratio of Heterodera rostochiensis on tomato was increased not only by high larval population density, but also by the presence of the three plant pathogenic fungi: Rhizoctonia solani, Verticillium alboatrum and grey sterile fungus. The sex ratio of H. rostochiensis increased with an increase in the fungus inoculum.

The Effect of Predator Age and Prey Defense on the Functional Response of Podisus maculiventris Say to the Density of Hyphantria cunea Drury

AbstractExperiments were designed to find the functional response (response per predator) of the pentatomid Podisus maculiventris to the population density of larvae of the fall webworm, Hyphantria cunea. The response was measured in confined universes, (glass jars), representing webworm nests, and it was found permissible to vary universe size, within certain limits, in order to obtain a wide range of prey densities without handling large numbers of larvae. The “disc equation” proposed by Holling (1959) was found to describe the response curves, except at very high prey densities, and to provide a satisfactory biological explanation for their decreasing slopes. P. maculiventris ingests about 84% of its own weight for each fifth-instar larva of H. cunea attacked successfully, and the time spent in feeding and becoming hungry enough to make another attack reduces very substantially the time devoted to searching activities. Both prey defense (Fig. 1) and the age of the adult predator (Fig. 2) have very important effects on the functional response curves and on the values of the parameters, a and b, of the disc equation. These effects are explained. The “rate of discovery”, a, is contrasted to Nicholson's (1933) “area of discovery” and it is shown why the former is more likely to be independent of prey density than the latter.In view of the population of webworm larvae in the average nest, it is concluded that the functional response of the various predators inside the nest is probably not important, and that attention should be devoted instead to the functional and numerical responses of predators and parasites to the density of nests per unit area. Because of the vigorous defense exhibited by fifth-instar webworm larvae, predation by timid predators like P. maculiventris is selective and larvae whose development is delayed by parasitism are likely to suffer more predation than healthy larvae.

Investigation on the population density of larvae of Cicada in the soil of apple orchard, and test on control

Investigation on the population density of larvae of Cicada in the soil of apple orchard, and test on control

Influence of Larval Population Density on Fluctuation in Mosquito Numbers

RECENT ecological studies on culicine mosquitoes in and around a village in south-western Nigeria1 revealed that the numbers of Aedes aegypti fluctuated throughout the year in a manner which could not be correlated with the observed external environmental factors. During a preliminary survey it was established that this species was restricted to breeding within the village area in clay water-pots of the type used for collecting and storing water, but that it was absent from natural habitats in the surrounding rain forest. The fact that it showed a typically domestic breeding pattern facilitated a study of the population dynamics throughout the year, and the method used for obtaining an index of breeding intensity was as follows. A number of clay pots were placed in tha village and sampled weekly, the pre-adults (larvae and pupae) being removed for counting while the pots were cleaned and refilled with fresh water. The number of pre-adults found weekly was taken as an index of the changes in density of the breeding population within the village.

Competition between Brown Gene and its Wild Type Allele in <i>Drosophila melanogaster</i>

1. The relative viability of brown homozygote was measured in various levels of larval population density which paralleled with the number of female parents in a culture bottle. The results were shown in Table 1 and Fig. 1, and confirmed the fact that the superiority in viability of brown homozygote increased with larval population density.2. Two series of competition experiments were conducted: series S, in which ten or less parental flies were sampled generation after generation, and series L, in which generally larger number of parents were sampled. By assuming that the zygotic selection coefficients were determined only by the relative viability of three genotypes, and by using Fig. 1, random change in frequency of brown genes were calculated from generation to generation.3. In both series the distributions of the amounts of random change relative to expected standard deviation of change in gene-frequency could be regarded to have mean values of 0. This result showed that the above assumption was practically correct.4. Average effective population size was considered to be smaller than average apparent size (N) on account of, at least, three factors, i, e., (i) the departure of parental sex-ratio from one-to-one, (ii) the variability of the numbers of progeny of each parent and (iii) the parental inbreeding. Thus, the formulaN=αβN.was presented, where α (0<α≤1) and β (0<β≤1) were the coefficients measuring influences of the factors (i) and the other factors, respectively.5. The values of α and β, and those of their poducts were calculated as follows:Series S: α=0.84, β=0.35-0.62, αβ=0.29-0.52.Series L: α=0.92, β=0.22-0.30, αβ=0.20-0.27.The values of β, especially in series L, seemed to be too small in comparison with the results of several antecedents. It could be interpreted, at least in part, as a result of circumstances that the number of effective parents was only a small fraction of total parents sampled; and such circumstances were considered to be remarkable in crowding condition as in series L.

The Effects of Larval Population Density on Some Laboratory Characteristics of Anopheles quadrimaculatus Say

The demonstration of the role of mosquitoes as disease vectors provided the impetus for extensive studies of these insects as laboratory animals. Notwithstanding, there has been little progress toward what might be termed the standardization of the mosquito for laboratory purposes. In particular, there may be considerable variation in the biting characteristics and behavior of Anopheles quadrimaculatus, even under well controlled laboratory conditions. Since preliminary work indicated that larval development has specific effects on the adult mosquito, the present studies were undertaken in an attempt to define some of the intrinsic factors which affect the laboratory biology of A. quadrimaculatus. This report deals with the effects of two extremes of larval population densities on some morphological and physiological characteristics of this mosquito, and the effect of copulation on the avidity of the female for a blood meal.