Insect Population Density Research Articles

친환경농업 시범마을에 대한 환경영양평가

1999년부터 2001년까지 3년간 친환경농업 시범마을에 적용되고 있는 INM (Integrated Nutrient Management) and IPM (Integrated Pest Management) 실천에 따른 추진효과를 분석하기 위하여 시범마을로 지정된 옥천과 양평지역의 농가 포장에서 시비량, 양분유실 및 생태계 변화 등을 조사 분석하였다. 3요소 시비량은 토양검정시비로 인하여 농가관행시비와 비교하여 <TEX>$28.6{\sim}39.4%$</TEX> 절감할 수 있었으며, 쌀 수량도 시비량이 비교적 적은 토양검정 시비구에서 <TEX>$3{\sim}10%$</TEX> 증수하였다. 영농기간동안 토양 침투수중 <TEX>$NO_3-N$</TEX> 농도는 농가관행 시비구 2.9 mg/L에 비하여 토양검정 시비구는 1.5 mg/L로 감소하였으며, 시범마을 논으로 유입되는 관개수의 COD, <TEX>$NH_4-N$</TEX>, <TEX>$NO_3-N$</TEX> 농도는 각각 15.0, 0.67, 1.39 mg/L, 시범마을 논에서 배출된 용수는 각각 12.4, 0.29, 2.42 mg/L로 감소되는 경향이었다. 처리별 수서곤충, 환형동물, 패류 및 감각류 등의 개체수는 농가관행구 100에 대하여 토양검정 시비구 295, 토양검정과 개량제 혼용구 276, 무비구 90으로 토양검정 시비구에서 많았으며 수서 무척추 동물은 관행농업을 수행하고 있는 지역을 100으로 볼 때 친환경농업마을은 242와 443으로 INM과 IPM을 실천하는 시범마을에서 생물종이 다양하고 그 개체수가 많은 것으로 나타났다. 친환경농업 시범마을 조성 후 작물 추천시비량 준수와 적기 예찰을 통하여 필요이상 사용되는 비료와 농약을 절감하여 생태계의 개선과 토양이 건전화된 것으로 평가되었다. In order to preserve the soundness of agro-ecosystem and products safety in agriculture, this study was evaluated environmental impact in relation to the INM (Integrated Nutrient Management) and IPM (Integrated Pest Management) at paddy fields at Ok-Chun and Yang-Pyung region. By introduction of INM with the application of BB(bulk-blanded) fertilizer based on soil analysis and IPM, the application rate of fertilizer was reduced to about <TEX>$28.6{\sim}39.4%$</TEX> and the yield of brown rice was increased to about <TEX>$3{\sim}10%$</TEX> compared to conventional practices. The concentrations of COD, <TEX>$NH_4-N$</TEX>, and <TEX>$NO_3-N$</TEX> in irrigation water flowed to the environmental-friendly agriculture practices were 15.0, 0.67, and 1.39 mg/L, respectively. The concentrations of COD, <TEX>$NH_4-N$</TEX>, and <TEX>$NO_3-N$</TEX> from paddy fields in drainage water were 12.4, 0.29, and 2.42 mg/L, respectively. The total number of the freshwater invertebrates was higher in field treated with fertilization by prescription with soil testing. Also, the population density of aquatic insects was higher than the other fields at both demonstration villages. In conclusion, it was possible to reduce the amount of fertilizer and agricultural chemicals application, and increase the yield of rice by application of the environmental-friendly agriculture practices.

Effects of Weeding on the Population of Insect Pests and Yield of Soybean (Glycine max (L.) in Calabar, Nigeria

Field experiments were conducted in the 1999 and 2000 late planting seasons to investigate the effects of weeds on the population of insect pests and yields of soybeans. Two soybean cultivars TGX 536-02D and TGX 1448-313D were planted as the main plot treatment while four weeding schedules (no weeding, 1, 2 or J weedings) were included as the sub-treatments. Some of the insects that were observed in the experimental plots included the defoliators such as: Medythia quaterna, Podagrica sp., Zonocerus variegatus The pod feeders among which were: Aspavia armigera, Nezara viridula, Acrosternum acuta, Cletus notatus, Mirperus sp, Riptortus dentipes and Chnootriba similes. The flower feeder such as Paederus sabeaus and the leaf roller (Hedylepta indica) were also observed. The weeded plots had significantly (P&lt;0.05) lower insect pest population densities than the non-weeded plots Insect population density decreased significantly with increase in the number of weeding. Thus, insect population of 6.23/0.6 m-row were observed in the plots weeded thrice in 1999 and 11.34/0.6 m in the year 2000, 7.01 and 12.30/0.6 m row in the 2-weedings while the l-weeding gave 9.35 and 15.87/0.6 m row. The non-weeded plot had 11.8 and 17.02 insects/0.6 m row. The frequency of weeding was highly correlated with the insect population. Grain yields were significantly higher (1286.84 and 858.77 kg/ha) in the two years when weeding was done three times compared with when no weeding was done or with when weeding was done once and twice. In the two years, the percentage unfilled/damaged pods decreased as the number of weeding increased (r=0.986 and 0.935). There was also an indication of a high correlation (r=-0.961 and -0.938) between insect population and the grain yields in the two years.

Effectiveness of protein‐rich pea flour for the control of stored‐product beetles

AbstractProtein‐rich pea flour is toxic to many stored‐product insects. We investigated several factors that may affect the efficacy of protein‐rich pea flour: insect species, insect population densities, grain species, temperature, and moisture. Adult Sitophilus oryzae (L.) (Coleoptera: Curculionidae) was more susceptible to protein‐rich pea flour than Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae). Protein‐rich pea flour did not increase the mortality of adult Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). However, it reduced the number of offspring of all three species. The toxicity of protein‐rich pea flour was not reduced after 9 months when stored at −15 °C, or at room temperature as flour or mixed with grain. Its toxicity in wheat increased with higher temperature and at lower grain moisture contents. Protein‐rich pea flour was more toxic in wheat and barley than in maize. This difference among grain species was not due to the kernel size of the grain, as ground wheat or maize with the same particle size still had different LD50s.

환경농업 시범마을 논에서 시비에 따른 무척추동물 개체 수 변화

This study was conducted to survey and identify kinds and population of the freshwater invertebrate fauna according to the managements of paddy rice fields at Ok-Chun and Yang-Pyung. The experiment was conducted in 4 paddy plots; conventional fertilization plot (CF), fertilization by prescription with soil testing with (ST+A) or without soil amendment (ST), and no fertilization as the control. In addition, the freshwater invertebrate fauna was also surveyed at 3 sections of as upper, intermediate and down, in both Jitan and Bungsan stream. The total number of the freshwater invertebrates was higher in the order of ST>CF>ST+A>C and ST>ST+A>CF>C at Ok-Chun and Yang-Pyung, respectively. The population density of aquatic insects was higher in plots fertilized by prescription with soil testing than in the other plots at both demonstration villages. The freshwater invertebrates collected in Jitan and Bungsan stream were identified and classified into 59 families and 90 species, and their population density was highest in the downstream among.

Field resistance of two soybean germplasm lines, HC95-15MB and HC95-24MB, against bean leaf beetle (Coleoptera: Chrysomelidae), western corn rootworm (Coleoptera: Chrysomelidae), and Japanese beetles (Coleoptera: Scarabaidae).

Two recently released, Mexican bean beetle, Epilachna varivestis, Mulsant, resistant soybean, Glycine max (L.) Merrill, germplasm lines, HC95-15MB and HC95-24MB, were examined for foliar and pod feeding resistance to adult bean leaf beetles, Cerotoma trifurcata (Forster), western corn rootworms, Diabrotica virgifera virgifera LeConte, and Japanese beetles, Popillia japonica Newman. Both lines were planted along with a susceptible control cultivar in 18 by 30-m plots and separate 0.8-ha size fields. Insects were sampled on a weekly basis with a sweep net. In late summer, defoliation ratings were recorded along with data on percentage pod feeding. Although a few significant differences in insect densities were obtained among the soybean lines on some sampling dates, no specific trends were observed in the ability of the resistant germplasm to reduce insect numbers. Insect population densities were similarly on all lines. However, both resistant lines were able to reduce defoliation during the growing season. Conversely, percentage pod feeding was similar among all the soybean lines, with no differences observed. The resistant germplasm lines appear able to lower levels of defoliation, and thus, offer a potential management tactic where leaf feeding, i.e., defoliation, is of concern. However, their ability to greatly reduce beetle population densities, and for the bean leaf beetle, to reduce pod feeding, appears limited.

In-Field Monitoring of Beneficial Insect Populations in Transgenic Corn Expressing a Bacillus thuringiensis Toxin

In 1998 and 1999, field studies were conducted near Rosemount, MN to assess the potential impact of transgenic sweet corn, transformed to express the Cry1Ab toxin from Bacillus thuringiensis Berliner var kurstaki (i.e., Bt corn), on several beneficial insects, including predatory coccinellids, chrysopids and anthocorids. Beneficial insects in both Bt and in non-Bt sweet corn were also monitored in field cages in 1999. Plants were visually sampled for beneficial insects by arbitrarily selecting 3 consecutive plants from each plot or 6 plants/cage. Rank transformed data were analyzed using the Kruskal-Wallis test, which indicated no significant within-year differences in the overall density of beneficial insect populations between Bt and non-Bt sweet corn. Coleomegilla maculata (DeGeer) was the dominant predator species detected in 1998 and 1999. A significant trend (P &amp;lt; 0.05) was found for C. maculata larvae in open plots, with non-Bt treatments having higher C. maculata levels than Bt. Also, C. maculata larval and adult densities, for caged plots, showed a significant trend for higher counts in the in non-Bt corn. No additional differences in species diversity of beneficial insects were detected using Hills N1. Neither Hippodamia convergens Guérin-Ménville, Adalia bipunctata (L.), nor Coccinella septempunctata L. were observed during 1999. Although our test detected significant trends for higher densities of C. maculata in non-Bt corn, the results also suggest that longer-term in-field studies with higher sample sizes are needed to further characterize what may be relatively subtle population effects in the field.

Genotypic variability and mode of action of Colorado potato beetle (Coleoptera: Chrysomelidae) resistance in seven Solanum species.

Accessions from seven wild Solanum species were evaluated in the field for resistance to the Colorado potato beetle, Leptinotarsa decemlineata (Say). The multivariate insect population density data were analyzed using factor analysis. The factors extracted corresponded to relevant phases of the insect's life cycle and provided information on the mode of resistance (antixenosis and antibiosis) of the plant species. S. berthaultii, S. capsicibaccatum, S. jamesii, S. pinnatisectum, and S. trifidum demonstrated both antixenosis and antibiosis but expressed different levels of resistance. The mode of resistance of S. polyadenium seemed to be antibiosis and that of S. tarijense antixenosis. Genetic variability and heritability of insect resistance traits within accessions was trivial or inconsistent for all Solanum species studied.

Effects of weed management systems on canopy insects in herbicide-resistant soybeans.

The effects of transgenic herbicide-resistant soybean varieties and their corresponding weed management strategies on canopy insects were examined in studies at two locations in Iowa in 1997 and 1998. Weed management systems that allowed more weed escapes typically had higher insect population densities. However, systems with fewer weeds seemingly were preferred by potato leafhoppers. Bean leaf beetles and potato leafhoppers showed preferences for certain soybean varieties, but these effects were attributed to soybean plant height. These findings indicate that although the transgenic soybean varieties did not strongly affect insect populations, weed management systems can affect insect populations in soybean. However, this impact is likely related more to weed suppression effectiveness than to a direct effect of the herbicides on the insects.

Estimation of Local Mean Population Densities of Japanese Beetle Grubs (Scarabaeidae: Coleoptera)

Insect populations tend to be patchy in distribution. Even when the mean population density is low, there may be local patches with high densities. As a result, estimates of mean populations may provide little information about the size or intensity of local patches within the sampled area. We compared the following 3 methods of estimating local population densities of insects: (1) with moving averages, a local mean population density is estimated as the mean of samples taken within a given radius of a central point, (2) with inverse distances, local means are estimated as weighted averages of samples; each sample is given a weight proportional to a power of the reciprocal of its distance from the center of the region for which the mean is to be estimated, (3) kriging is a geostatistical algorithm for estimating local means as weighted averages of samples. Weighting is based on the spatial covariance of the samples, or the degree to which samples that are near to each other are related. The first 2 methods are relatively easy to calculate but were unreliable when used with standard parameters to estimate local Japanese beetle grub densities. When an optimum radius was used with moving averages and an optimum exponent was used with inverse distances, the advantage of ease of calculation was lost, yet both methods were still inferior to kriging in providing accurate estimates of local means.

Predicting insect density from probe trap catch in farm-stored wheat

Insect populations infesting wheat stored in four bins on two Kansas farms were monitored from early July 1996 through to the middle of January 1997. Estimates of adult insect density based upon the numbers of adult insects caught using probe traps differed from those based upon the number of insects found in grain samples. These differences were a result of differences in numbers of insects found and percentages of traps or grain samples with insects. Traps detected insects 15 to 37 d earlier than grain samples. The depth of traps below the grain surface tended to influence both the total number and species composition of the insects that were caught. Traps inserted with the top just below the grain surface collected an average of 1.9 times more Cryptolestes ferrugineus (Stephens), 1.2 times more Rhyzopertha dominica (F.), 4.1 times more Ahasverus advena (Waltl) and 77.4 times more Typhaea stercorea (L.) than traps inserted with the top 7.6 cm below the grain surface. However, trap depth did not have a significant effect on the number of R. dominica caught and on only 12 to 21% of sampling dates did trap depth have a significant effect on the number of insects of other species that were caught. Grain temperatures in three of the bins averaged 30 °C during the first 70 d of storage and then decreased by 0.2°C/d. Grain in the other bin was initially more than 10°C warmer and grain temperature decreased by 0.2°C/d over the full storage period. The numbers of insects captured in traps decreased as grain temperature decreased even though grain samples indicated that insect populations were still growing. Thus, trap catches did not estimate insect population density consistently throughout the storage period. A method was developed in the current paper to adjust for the effect of seasonal changes in temperature on trap catch.

EVALUATING THE IMPACT OF INSECT COMMUNITY ON PINE CATERPILLAR DENSITY IN DIFFERENT STAND CONDITIONS

Abstract Natural enemies play an important role in inhibiting population growth of pine caterpillar, but they are difficult to be used in systematic management models. This paper attempts to use some forest stand factors to substitute the effect of natural enemies, which could be used in management models. Through the studies from more than 200 stand plots with different stand conditions in Qu County, Changshan County, and Longyou County of Zhejiang Province, 16 predominant species groups from insect community were selected, and the canonical correlation coefficient between the diversity index, species number, individual number of predominant species and the stand factors was analyzed. The results indicated that the canopy density and ground vegetation were the key stand factors for characterizing the function of insect community. The forest area was divided into four types according to the variation of canopy and vegetation conditions by using cluster analysis. The regression models between the rate of variation of pine caterpillar density and the forest factors including canopy density and vegetation covers were developed in each type of forests. There were significant differences in diversity index, species number, individual number of insect community and population density of pine caterpillar among four types of forests, and correlation coefficients of the four regression models were rather high (r=0. 924 — 0. 964). This means that the classification of the forest stands is reasonable and the stand factors can characterize the effect of natural enemies in practice.

Modeling Winter Oilseed Rape Plant Infestation by Baris coerulescens (Coleoptera: Curculionidae)

Baris coerulescens Scopoli is a pest attacking the tap root of winter oilseed rape. Females lay eggs in the root crown for >3 mo. The slow accumulation of eggs in plants poses problems in defining cohorts for modeling larval development under fluctuating temperatures. The total number of immature individuals per plant was assessed throughout the whole reproduction period during a 4-yr study. Two supplementary data sets were collected in 1994 and 1996. Total insect population density plotted against degree-days (in base 10) differed among years. The speed at which the population maximum was reached was steeper during wet years than during dry years. The hypothesis was that the differences in slopes were caused by drought stresses, which were known to influence egg laying from experiments in controlled conditions. A model based on the Weibull distribution and describing the growth of insect population density per plant from the beginning of egg laying to maximum density is proposed. The insect population density is expressed as the cumulative proportion of individuals found in plants, varying in the interval (0,1). The initial degree-day scale is corrected by a coefficient linked to the upper soil water content. This correction ensured a good concordance among years and places. The model predicted correctly the dynamics of plant infestation under variable climatic conditions.

Factors Affecting the Natural Regeneration of Quercus in Scottish Oakwoods. II. Insect Defoliation of Trees and Seedlings

Defoliation of oak trees and seedlings (Quercus petraea and Q. robur x Q. petraea putative hybrids) by various lepidopteran species was investigated in two upland semi-natural oakwoods (Dinnet and Ariundle National Nature Reserves) within contrasting climatic zones in the Scottish Highlands. Experiments were designed to test four hypotheses: the failure of oak to regenerate naturally is partly attributable to defoliation of seedlings by insects; seedling defoliation is linked to canopy density and composition; the degree of seedling defoliation is linked to the extent of canopy defoliation; and defoliation is positively correlated with insect population density in the canopy. The extent of canopy defoliation of oak was significantly different between the two woods, with trees at Ariundle, located within a wetter climatic zone, more defoliated than those at Dinnet, which is in a drier climatic zone. Defoliation also varied significantly between individual trees and between years. Defoliation was positively correlated with degree of infestation by the larvae of several lepidopteran species. Leaf samples at Dinnet were dominated by Operophtera brumata, and those at Ariundle by Erranis defoliaria. The degree of infestation was higher at Ariundle. Experimental seedlings were significantly more defoliated under oak canopy than in the open or under a Betula spp. canopy. Canopy defoliation was positively correlated with defoliation of seedlings growing directly beneath, but seedling defoliation was negatively correlated with oak canopy density. Defoliation of oak seedlings by insects poses more of a threat to the natural regeneration of oak at Ariundle than at Dinnet, possibly due to climatic differences between these two woods. A group-felling system using coupe sizes of over 0.5 ha is recommended for encouraging oak regeneration in woods such as Ariundle, where seedlings need to be kept free from the influence of an overhead oak canopy. Shelterwood systems, where seed trees are retained after extensive thinning, are not recommended. In woods similar to Dinnet, both group-fell and shelterwood systems are appropriate management options. Woodland managers should be aware of defoliation problems within their woods before deciding on which silvicultural option to choose.

Larval feeding behaviour affects the impact of staminate flower production on the suitability of balsam fir trees for spruce budworm.

Laboratory rearing of spruce budworm, Choristoneura fumiferana, in conjunction with field rearing indicated that the feeding behaviour of the larvae, which is affected by the insect population density, significantly influenced the impact of balsam fir, Abies balsamea, staminate flowering on spruce budworm biology. At low budworm density, the production of pollen in the midcrown of host trees reduced the insect development time by 5 days without affecting pupal weight, fecundity and survival. However, at high budworm density, the small amount of current-year foliage produced by flowering branches forced old larvae (sixth instar) either to feed on 1-year-old foliage (backfeeding) or to move from the midcrown to the lower crown section where staminate flowers are absent and more current-year foliage is available. When old larvae fed on old foliage, they exhibited reduced pupal weight and fecundity without losing the advange in development time that they obtained from feeding on pollen during their early stages of development. On the other hand, when old larvae moved to the lower crown section, they avoided the negative effects of backfeeding but lost the advantage in development time that was gained from feeding on pollen. Results from this study indicated that the production of staminate flowers by balsam fir trees could have opposite effects on spruce budworm population dynamics depending upon the insect population density when flowering occurs.

Coastal insect herbivore communities are affected more by local environmental conditions than by plant genotype

Abstract. 1 We compared the effects of plant genotype and local environment on population densities of a community of coastal insect herbivores in west-central Florida. Reciprocal transplants of four genotypes of three species of coastal plants, Borrichia frutescens, Iva frutescens and Limbricata, were made in July 1992 between a series of off-shore islands. 2 For each plant species, phytophagous insects with a wide range of feeding modes including gall-makers, stem borers, leaf miners and sap suckers were affected more by local environment than by plant genotype. Whereas host genotype had a significant effect on the population densities of gall-makers on B.frutescens in the spring of 1993, no significant effect on the denrities of any other insect species was found and the effect on the gall-makers on Borrichia disappeared in the summer, 1 year after the transplants had been made. In our study, local environment had by far the greatest effect on insect population densities among islands. This is an unusual result because in other studies over 80% of the insect species examined have been affected by plant genotype (Karban, 1992). This result is consistent with that reported by Stiling (1994), who censused populations of two phytophagous insects on reciprocal transplantr ot Borrichia in north Florida. 3 Local environment also had an effect on insect population densities within islands. This result contrasts with similar studies performed in north Florida (Stiling, 1994), where population densities did not differ within areas, and underlies how some biotic processes may change with in the same community even over relatively small changes in species range.

Impact of milling degree on Liposcelis paetus population growth rate and assessment of milled rice weight loss due to infestation

Liposcelis paetus can survive and breed on milled rice, causing a small dry-weight loss to the commodity. The extent of the losses was found to be dependent upon the degree of milling and the insect population density. The rate of population increase was greater on lightly milled rice (slope = 0.042) than on well-milled rice (slope = 0.028). After 14 weeks' infestation, greater weight losses were incurred in the lightly milled than the well-milled rice (2.88 and 1.20%, respectively). A postinfection decrease in lipid and, to a lesser extent, protein content was detected in the lightly milled samples (35.88 and 3.59%, respectively).

Epizootiological study ofNeozygites parvispora (Zygomycota: Entomophthoraceae) in a population ofFrankliniella occidentalis (Thysanoptera: Thripidae) on pepper in sicily

This paper describes an epizootic of the entomopathogenic fungusNeozygites parvispora occurring in a population ofFrankliniella occidentalis in a pepper crop under plastic-house, in south-eastern Sicily (Italy). The progress of the epizootic in the thrips population was monitored weekly, from December 1990 to April 1991. Infections ofN. parvispora caused up to more than 60% mortality of the mobile developmental stages of the thrips, reducing consistently both the insect population density and the proportion of flowers and leaves infested by thrips. All mobile developmental stages of the thrips (adults, 1 st- and 2nd-instar larvae) were susceptible to the infections ofN. parvispora. The incidence of mycosis in each developmental stage was positively correlated with its respective proportion in the thrips population.

Weed and herbivorous insect population densities at the broad spatial scale: Ambrosia artemisiifolia L. and Zygogramma suturalis F. (Col., Chrysomelidae)

AbstractZ. suturalis was introduced into Russia in 1978 to control against the common ragweed. Weed and insect population densities were estimated in 1988–1989 over 250 km2. Absolute (beetles per m2) density of Z. suturalis was almost linear with the ragweed density (wet weight per m2). Relative (beetles per kg of ragweed) density was independent of ragweed density. Last year's absolute density of Z. suturalis significantly influences current relative insect density, but its influence on the absolute insect density is overpowered by the influence of the current ragweed density. Obviously, just the plant and not the insect is the driving force in their interactions. The introduction results can be considered as establishment and moderate biological success, but not as control success. Host impact is very low because of low relative population density of Z. suturalis. Local patches with high Z. suturalis density, which are usually located in field margins, do not play an important role in total population density determinations. Possibly, field nurseries, i.e. large uncultivated sites grown with ragweed, could be a promising method of Z. suturalis propagation.

Analytical Population Dynamics

Despite considerable effort, ecologists still have an incomplete understanding of the processes that cause changes in insect population densities. Although there have been significant advancements in the development of theoretical population models, considerable debate still exists on how to deduce the underlying processes that drive the dynamics of natural populations.

Testing Insect Population Density Relative to Critical Densities with 2-SPRT

Sequential sampling plans are appealing because fewer observations are needed than those needed for fixed sampling plans to make a terminating decision when insect populations are sparse or abundant. Wald's Sequential Probability Ratio Test (SPRT) commonly has been used in monitoring insect populations and damages from these populations. At times, particularly for moderate infestations, the SPRT with its parallel boundaries takes longer than a comparable fixed-sample-size method to make a terminating decision. An alternative sequential testing procedure called the 2-SPRT for the negative-binomial parameter P is demonstrated. The value of the exponent k is assumed to be known. In this procedure two one-sided SPRTs are performed simultaneously, which results in the convergent boundary lines. The average number of observations needed for the terminating decision for medium infestations (i.e., for P 1 < P < P 2 ) is observed to be considerably smaller than that for the SPRT with a slight increase in sampling effort when infestations are light or heavy. An application of the 2-SPRT is demonstrated using cotton f1eahopper, Pseudatomoscelis seriatus (Reuter), data obtained in southwestern Oklahoma.