Summer Population Research Articles

Body Mass of Roe Deer Fawns during Winter in 2 Contrasting Populations

Because first-year survival and age at sexual maturity of northern ungulates often depend on body mass of fawns during winter, knowledge of factors affecting body mass of fawns is necessary to understand population dynamics and management of ungulates in temperate regions. Therefore, we compared body mass of roe deer (Capreolus capreolus) fawns during winter in two enclosed populations with contrasting climatic and demographic characteristics: Chize (CH) in western France (mild winters, less abundant food and lower birthrates), and Trois Fontaines (TF) in eastern France (cold winters, abundant food and high birthrates). We weighed 2,077 fawns (1,212 in TF and 865 in CH) of both sexes captured with drive-nets in January and February from 1976 to 1993. Mass of male fawns was greater than of females in both populations (P < 0.01). Body mass varied among years for both sexes in each population (P < 0.01 in CH; P < 0.01 in TF). Neither climatic conditions between April and December nor population density accounted for yearly variation in body mass of fawns in TF. Rather, body mass fluctuated randomly about a mean, with no longterm effects on population dynamics. By contrast, body mass of fawns in CH was correlated with mean daily temperature in June-July (P = 0.01 for males; P = 0.04 for females) and population density (P = 0.02 for males; P = 0.03 for females). Body mass of fawns was greater in years following cool summers and in years of low population density (r 2 = 0.75, P < 0.01 for males; r 2 = 0.50, P = 0.02 for females). Mass of male fawns but not female fawns was greater in January-February when total rainfall in the previous April-May was low (P = 0.01). In CH, yearly variation in fawn body mass supports the range quality hypothesis which states that fawns entering winter are small owing to poor nutritional conditions the previous summer or high population density. As a consequence, yearly variations in body mass probably have long-lasting effects on population dynamics in CH.

Apple, Comparison of Insecticides Against Oblr, 1995

Abstract Treatments were applied with a truck-mounted airblast sprayer to 0.25 acre plots of apple trees in two orchards: (1) ‘Idared’, ‘Cortland’ and ‘Empire’ trees (VanFleet orchard), which were ca. 4 years old, 5 ft high, and planted 8 by 12 ft apart; (2) ‘Idared’ (Nesbitt orchard), which were ca. 8.0 ft high and planted 15 by 18 ft apart. Treatments were arranged in a RCB design and replicated twice in each orchard. Complete seasonal schedules of Asana, Dipel, Lorsban, and Confirm were compared in which the first spray was applied at the estimated first OBLR egg hatch (21-23 June), followed by 2 more protective sprays at 14-d intervals. Early schedules of Asana and Confirm were compared in which only 1 spray was applied at the estimated first egg hatch (21-23 June). Also, a 2-spray schedule of Asana was tested in which the first spray was applied at the estimated first egg hatch (21-23 June) followed by one more spray 14 d later. Application volume was 100 gpa. Summer populations of larvae were compared by examining 20-50 growing terminals from each of 5 randomly selected trees/plot for live larvae on 11-12 Jul and on 25-26 Jul. Fruit damage from the first summer generation of larvae was estimated on 6-7 Aug and on 21-22 Aug by sampling 100-150 apples from each of 5 randomly selected trees/plot. Similar fruit samples were collected at harvest in each plot and classified in USDA grades of Fancy, #1, and culls.

A multiannual outbreak of the turbellanan Alaurina composita Mecznikow 1865 in the German Bight

The plankton time series of ‘Helgoland Roads’ has shown a multiannual population change in the abundance of the turbellarian Alaurina composita Mecznikow 1865. From the 1970s to the mid-1980s, the summer population increased by two orders of magnitude; since then, it has fallen by about one order of magnitude. As limnetic investigations in related species show, A.cornposita must be considered a key predator of the North Sea pelagial. Knowledge regarding the biology and ecology of the species is only rudimentary.

Growth and reproductive ecology ofPalaemon adspersus(Decapoda, Palaemonidae) in the western Mediterranean

abstract Aspects of growth and reproductive cycle of the prawn Palaemon adspersus were studied in Alfacs Bay (Ebro delta, western Mediterranean) . This species shows a marked sexual size dimorphism. Sexual differences related to length-weight were noted. The sex-ratio observed was significantly biased towards females in the study area. Cohort analysis of the size-frequency distributions suggests the occurrence of a main recruitment period in the study area during August and September. The estimated von Bertalanffy growth parameters suggest rapid growth for both sexes. Ovigerous females were recorded between January and September. Those carrying eggs about to hatch appeared from March. Some of the early specimens appearing in the benthic population in summer (yearling individuals) had already spawned at the end of the reproductive period, together with prawns from the previous generation (wintering individuals).

Bot Fly (Cuterebra fontinella fontinella) Parasitism of Cotton Mice (Peromyscus gossypinus) on St. Catherines Island, Georgia

From February 1993 through October 1994, 382 cotton mice (Peromyscus gossypinus) were live-trapped and examined for bot fly (Cuterebra fontinella fontinella) larvae. Thirty-nine (10%) of the mice were parasitized by a total of 44 bot fly larvae. All bots were situated in the inguinal or lower abdominal region of the mice. Monthly data strongly suggested that this bot is bivoltine at this latitude with distinct summer and winter population peaks. Prevalence of parasitism was highest in June 1994 when 56% of 16 mice examined were infested with a mean intensity of 1.3 bots. Adult flies were successfully reared from 10 bots that exited from mice; the time period (58-98 days, mean = 79.5) that these specimens spent in the soil as pupae further supports the contention that C. f. fontinella is bivoltine on St. Catherines Island.

Limitation of Collared Lemming Population Growth at Low Densities by Predation Mortality

Populations of the collared lemming (Dicrostonyx kilangmiutak) and the tundra vole (Microtus oeconomus) have been at consistently low densities, and non-cyclic, at Pearce Point, Northwest Territories, Canada, for six yr. In most summers population densities decline, or only increase marginally, despite ongoing reproduction. We investigated the hypothesis that predation mortality is sufficient and necessary to curtail lemming population growth in summer. To test predictions of the hypothesis, we compared lemming demography, using mark-recapture and radiotelemetry, on a population from which predators were excluded (PE), using a perimeter fence and aerial mesh of nylon (11.4 ha), with demographies of three control populations (18-25 ha). Predation was the proximate cause of the majority of adult and neo-natal mortality, and was not replaced in a compensatory fashion by any other mortality factor in the PE. Significantly fewer adult lemmings died in the PE, and consequently survival inside the PE was significantly enhanced. Recruitment of juvenile lemmings to the adult population was significantly higher in the PE on a per unit area basis. The lemming population in PE followed a significantly different trajectory than the control populations in 1990 and 1991, remaining fairly stable while controls declined. However, the protected population did not grow, apparently because of juvenile dispersal: telemetered juveniles dispersed at an average rate of 53 m/d within the first ten d after weaning. We believe that the protected area was too small to encompass such dispersal, and that emigrants were not replaced by immigrating juveniles since the latter faced heavy mortality outside the exclosure. In 1992, numbers on PE and all controls grew, in conjunction with a regional absence of rough-legged hawks (Buteo lagopus) and a scarcity of red foxes (Vulpes vulpes), the two principal microtine predators. Tundra vole population growth was also limited by predation mortality, but to a lesser extent. We conclude that predation mortality is sufficient and necessary to limit summer population growth in these microtine species.

Feeding rates and productivity of the copepod Acartia bifilosa in a highly turbid estuary; the Gironde (SW France)

Acartia spp. are the dominant copepod species in the Gironde estuary, seaward of the turbidity maximum area. Acartia bifilosa develop a large population in spring and early summer whereas Acartia tonsa appear in late summer. High values and high variability of chlorophyll a/suspended particulate matter ratio are found seaward of the turbidity maximum area. Feeding rates of A. bifilosa were measured by fluorometry. Phytoplankton ingestion was found to be highly variable, between 8 to 80% of copepod carbon body weight. Except for adult females, copepods were heavier in summer than in winter. PB ratios, estimated by the instantaneous growth rate method, varied from 0.03 d−1 to 0.14 d−1. The gut contents and P/B ratios of Acartia bifilosa were related to chl a/SPM ratio. From those data, and a few obtained for A. tonsa, it is concluded that only in summer months phytoplankton ingestion is enough to maintain secondary production.

Age structure and reproductive composition of summer Musca autumnalis (Diptera: Muscidae) populations estimated by pterin concentrations.

Pterins in face flies, Musca autumnalis DeGeer, were measured spectrofluorimetrically to estimate the chronological ages of adults in natural summer populations. The age distributions showed a systematic undersampling of young males. Exponential, Gompertz, and Weibull models were fitted to the age distributions. A 1-parameter exponential model suggested mean daily survival rates of 0.83 for female face flies, and a mean life expectation of 5.5 d. But the Weibull model best fit the age distributions, providing mean life expectations of 10.1 and 11 d for males and females, respectively. Ovarian dynamics were examined with respect to chronological age and delays were detected in vitellogenesis and oviposition. Face fly populations seemed to reproduce at less than the maximum rate allowed by prevailing temperatures, at which it was estimated that an average female would undergo 2.2 ovarian cycles and have a lifetime fecundity of 28.5 female progeny.

Seasonal, spatial and interannual variability in the reproductive dynamics of the grooved tiger prawn Penaeus semisulcatus in Albatross Bay, Gulf of Carpentaria, Australia: the concept of effective spawning

An index of population fecundity based on the abundance and fecundity of spawners was used to describe the spawning patterns of a population of Penaeus semisulcatus de Haan in the Albatross Bay region of the Gulf of Carpentaria, Australia. Between March 1986 and March 1992, 66 monthly sampling cruises were completed and a total of 133238 prawns were caught in 1986 trawls. Subadult females from the spring (August–November) spawning recruit to the offshore population in summer (December–January). Some of these mature and spawn in late-summerautumn (January–March) at ∼6 mo old, but most spawn in spring (August–November) at ∼12 mo old. The subadult females from the late-summer-autumn spawning recruit to the population in May–July, and some spawn in spring (August–November) at ∼6 mo old. As a result there is a mixture of 6 and 12-mo-old spawners in spring. The effective spawning periods for stock renewal, based on subsequent larval, postlarval and juvenile abundances, and recruits, are spring (August to November) and late summer (January–February). In 2 of the 6 yr, the spring and late-summerautumn spawning patterns were clearly bimodal; in the other years the late-summer-autumn peak was less distinct, although spawning continued over this whole period. Both the absolute and relative sizes of the seasonal peaks varied between years. Population fecundity was found to be a function of the complex interactions of the abundance and size structure of the females and the proportion of spawners. P. semisulcatus moves offshore and disperses between February and May. By May, most of the adults that recruited the previous summer are located offshore in depths >40 m. After July, they move to shallower waters (<40 m). In September–October they spawn, together with the component of autumn recruits, in depths of 20 to 35 m. The variation in seasonal, spatial and size composition patterns of the spawners provides the basis for description of the subset of the overall spawning stock (“effective spawners”) that contributes to subsequent recruitment.

Population status and breeding of New Zealand fur seals (Arctocephalus forsteri) in the Nelson‐northern Marlborough region, 1991–94

Abstract The population size, distribution, breeding, and onshore habitats of New Zealand fur seals in the Nelson‐northern Marlborough region, New Zealand, were investigated. Breeding occurs at four relatively new rookeries along the southern shores of Cook Strait: at Stephens Island in the outer Marlborough Sounds, at Archway Islands and Pillar Point near Cape Farewell, and at Tonga Island in Tasman Bay. These rookeries were established in about 1970, 1980, 1988, and 1988, respectively. In 1993–94 about 500 pups were born and the extant population breeding or born at the four rookeries was assessed as 2410. There were also 17 hauling grounds, each with 25 or more seals ashore in winter, and about 50 other sites where lesser numbers hauled out regularly. Comparison with earlier estimates indicates that the summer population increased from about 70 in 1973 to about 1000 in 1994—a sevenfold increase of yearling and older seals. The number of pups produced increased at a mean annual rate of 23% since 1970–71...

Aphid‐parasitoid interactions in a winter cereal crop: field trials involving insecticide application

AbstractLarge scale field trials were conducted to investigate aphid‐parasitoid interactions in winter wheat following spring applications of contact or systemic insecticides. Percentage parasitism was also investigated in the dominant aphid species using acrylamide‐gel electrophoretic methods. Sitobion avenae (F.) Metopolophium dirhodum (Walk.) and Rhopalosiphum padi (L.) were the commonest aphids and showed typical patterns of abundance through the growing season. Six parasitoid species were found: Aphidius rhopalosiphi de St.‐Per., A. ervi Hal., A. picipes (Nees) and Praon volucre (Hal.) being the most common primary parasitoids that attack the three main aphid species. The present work demonstrated a degree of temporal separation of these dominant cereal aphid parasitoid species which has rarely been documented. There was also evidence of earlier female activity in the crop in four of the six species. Parasitoid populations increased into June and peaked in July, coinciding with and continuing after peak aphid populations, before rapidly declining into August.Both contact and systemic insecticides sprayed in spring produced only a slight initial trend of suppression of aphid populations compared to control treatments; no influence on late summer populations was found. However, significant between‐field differences occurred. Neither contact nor systemic insecticides had any effect on population sizes, species composition or life history of aphid parasitoids (Braconidae; Aphidiinae, Aphelinidae) compared to control plots in the present study. Percentage parasitism was likewise unaffected by insecticides and reached a peak, based on electrophoretic methods, of 40% at peak aphid densities at the end of June. Estimates of parasitism based on presence of mummies were up to 10 times lower.Possible reasons for the lack of effect of insecticide application in the present study include timing of application (prior to main immigration period of aphids and parasitoids), mobility of populations and insecticide‐induced stimulation of reproduction in aphids.

Temporal Variation in Abundance of Peromyscus leucopus in Wooded Habitats of Eastern Kansas

-White-footed mice (Peromyscus leucopus) were sampled during spring, summer and autumn on the Konza Prairie Research Natural Area, Kansas, from autumn 1981 to spring 1988. Abundance was greater in gallery forest than in wooded outcrop habitat, although temporal patterns of abundance were similar with highs in 1981-1982 and 19851986. Standard deviations (SD) of the common logarithm of abundance were ' 0.32 for each of four sites in spring, summer and autumn, except for one forest site in spring. Our SD values were similar to those reported for other populations of P leucopus. Abundance of P leucopus was related to its abundance in the previous season (spring abundance vs. that in previous autumn, summer abundance vs. that in previous spring and autumn abundance vs. that in previous summer), seed production by woody vegetation and precipitation, but the factors that had a major influence on abundance of P leucopus varied among spring, summer and autumn populations. Ambient temperature was unrelated to abundance of P leucopus during each of the 3 seasons studied.

Apple, Comparison of Schedules Against OBLR, 1994

Abstract Treatments were applied with a truck-mounted airblast sprayer to 0.25 acre plots of apple trees in two orchards. In the LaMont orchard the ‘Tdared’ trees were ca. 12 years old, 12 ft high, and planted 12 by 30 ft apart. In the Brown orchard the ‘Tdared’ trees were ca. 13 ft high and planted 15 by 18 ft apart. Treatments were arranged in a RCB design and replicated twice in each orchard. Two control schedules were compared: An early schedule in which the first spray was applied at the estimated first egg hatch, followed by two more protective sprays, and a standard schedule in which the first spray was applied at 640 DD (base temperature = 50°F) after the first male flight followed by a second protective spray. Sprays were applied in 100 gpa of water except for the last sprays in the LaMont orchard, which were applied in 200 gpa of water. Summer populations of larvae were compared by examining 20-50 growing terminals from each of five randomly selected trees per plot for live larvae on 12-14 Jul and 2 Aug. Fruit damage from the first summer generation of larvae was estimated on 19-22 Aug by sampling 100-150 apples from each of 5 randomly selected trees per plot. Apples were also examined at harvest and classified in USDA grades of Fancy, #1, and culls to evaluate the severity of damage.

Observations on the pineal gland of the big brown bat, Eptesicus fucus: possible correlation of melanin intensification with constant darkness.

Our initial observation of the macroscopically pigmented pineal gland of the big brown bat, Eptesicus fuscus, led to this study. Information has been lacking on pigmentation in the pineal and its significance in mammals in general and bats in particular. This report begins to address this situation. Bats were examined both in the wild and after exposure to various experimental conditions. The pineals were examined macroscopically as well as with light and electron microscopy. The pigment was identified as melanin by its color, the ultrastructure of its granules, and their reaction with hydrogen peroxide. Gross observations showed the pineals to be variably pigmented, which were subjectively scored from unpigmented to heavily pigmented. Pineals from bats exposed to a continuous 24 h light regimen or those from a summer population contained very little, if any, externally visible melanin. Such pineals are considered unpigmented in this study. In contrast, pineals from 74% of 156 animals taken together, either subjected to constant darkness or hibernation (simulated or natural), exhibited very heavily pigmented pineals. The pigment in these cases even extended to the juxtapineal meningeal covering. The pineal was pigmented even in a newborn Eptesicus. The pineal pigmentation in the big brown bat appears to intensify with constant darkness and may vary seasonally. The observation of macroscopically pigmented pineals in some other bats (Myotis lucifugus, Pipistrellus subflavus, and Lasiurus borealis) suggests that this phenomenon may be of taxonomic value for the family Vespertilionidae (Order Chiroptera).

Binomial Sequential Classification Sampling Plans for Russian Wheat Aphid (Homoptera: Aphididae) Management: Robustness Varying with Tally Thresholds of Aphids in Sample Units

Binomial sequential classification sampling plans were developed for use in classifying populations of the Russian wheat aphid, Diuraphis noxia (Mordvilko), below or above a mean intervention-threshold density (>miT) for management decision making. Based on 4 yr of field data from summer and fall populations on wheat and barley in the northwestern United States, the proportion of tillers with no more than T (tally threshold) aphids (PT) was related to mean aphid density (m) with an empirical model in the form of In[-In(PT)] = a + b ln(m) and the negative binomial distribution. Three mean intervention threshold (mIT) values (one, five, and 10 aphids per tiller) with a series of T values were used to satisfy needs for control of aphid populations varying in density at different crop stages. The sampling plans were evaluated using operating characteristic and average sample number functions computed using the empirical PT − m model or the negative binomial distribution model. The robustness of the sampling plans improved with increasing T values. When using empty tillers (T = 0), the resulting sampling plans were not robust for all mIT values considered. Based on the operating characteristic and average sample number functions, the recommended T values for use are 2-4 for crops at stages before the end of booting given mIT = 1, 15-25 for crops at stages before heading given mIT = 5, and 20-40 for crops at stages after heading or flowering given mIT = 10. Sampling stop lines for each mIT and T are provided along with a discussion of their application to sampling aphid populations in the field.

Seasonal variations in distribution and population structure of Microcalanus pygmaeus and Ctenocalanus citer (Copepoda: Calanoida) in the eastern Weddell Sea, Antarctica

The abundance, vertical distribution and population structure of two important small calanoid copepod species, Microcalanus pygmaeus (G. O. Sars) and Ctenocalanus citer Heron and Bowman, were studied in the eastern Weddell Sea in summer (January/February 1985), in late winter/early spring (October/November 1986) and in autumn (April/May 1992). The population of Microcalanus pygmaeus consisted mainly of copepodite stages CII and CIII in late winter/early spring and were concentrated between 500 and 200 m depth. In summer, stage CIV was the modal stage and the bulk of the population had ascended above 300 m. In autumn the population structure was bimodal with CI and CV dominating. Most of the population was concentrated between 300 and 200 m. In all investigation periods M. pygmaeus had their maximal concentrations in the thermo-pycnocline. The developmental stages CIII to CV of Ctenocalanus citer formed the bulk of the population in late winter/early spring. In October all developmental stages had their main distribution between 500 and 200 m, except females, which were concentrated in the upper 50 m. In November most of the population occurred between 200 and 50 m. The summer population was concentrated in the upper 50 m, and numbers increased dramatically as the new cohort hatched. Copepodite stages CII and CIII dominated the population at the end of January, while CIV dominated 2 wk later. In autumn, CV was the modal stage. The majority of the population was concentrated in the upper 100 m, but there was an increase in abundance below 300 m compared to summer. Age structure changed with depth with a younger surface population and an older one in deeper water layers. The seasonal change in number of M. pygmaeus is much smaller than that of C. citer; the summer:winter:autumn ratio of the former being about one, whereas the winter:summer/autumn of the latter was about nine. Early copepodite stages and adults of M. pygmaeus occurred throughout all investigation periods. The large proportion of early copepodite stages in April and in mid-October suggests autumn and early to midwinter breeding. Apparently, M. pygmaeus may reproduce and grow year-round or perhaps has a 2-yr life-cycle. In contrast, the dramatic increase in abundance of early copepodite stages of C. citer in summer suggests springtime reproduction.

Genetic Structure in Migratory Populations of the Bat Tadarida brasiliensis mexicana

The genetic structure of eight summer and four winter colonies of the migratory bat ( Tadarida brasiliensis mexicana ) was examined to test the hypotheses that migratory populations are genetically distinct and that maternity colonies are composed of bats from genetically differentiated breeding colonies. Samples from seven of the summer colonies included only lactating females that were resident with their young in maternity roosts. Samples from winter colonies included adult males and adult females. Males and females were analyzed separately. Data from six polymorphic allozymic loci showed no statistically significant differences in allelic frequencies among colonies. Standardized genetic variances were low among all summer colonies (Fst = 0.008) and higher among the winter colonies of males (Fst = 0.016) and females (Fst = 0.021). Cluster analysis based on genetic similarity provides no evidence that summer or winter populations are structured genetically into distinct geographic units. Analysis of genotypic distributions within colonies also provides no evidence that maternity colonies consist of bats from genetically differentiated breeding colonies. Data from 38 loci for a single summer colony showed that this colony contains a high level of genetic variability, as expected in an organism with a large, genetically effective population size.

Growth and Reproductive Biology of Palaemon xiphias Risso, 1816 (Decapoda: Caridea: Palaemonidae)

ABSTRACT Aspects of growth and reproductive cycle of the prawn Palaemon xiphias were studied in Alfacs Bay (Ebro delta, Spain) from December 1989 to December 1990. Growth is continuous throughout the year. Adult females are larger than males. Sexual differences related to length-weight were noted. Longevity was estimated to be 14-17 months. The growth equation estimated for males is: L, = 50[1 - exp{–1.57(t + 0.31) - ((0.45)(1.57)/ 2π)sin(2π(t – 0.9))}] and for females L, = 70[1 - exp{–1.92(t + 0.15)((0.6)(1.92)/2π)sin(2π(t - 0.9))}], where L, is length (mm) at age t (in units of years). Ovigerous females were recorded between April and October. They were most numerous in May and June. Some of the early specimens appearing in the benthic population in summer had already spawned at the end of the reproductive period. The number of spawnings by a single female was a minimum of two. The number of eggs (range: 318-2,750) carried by females was related to their size: y = 0.000727x3.5868; r = 0.91752; N = 30, where y = egg number and x = total female length (mm).

Residues of lead, cadmium, and arsenic in livers of Mexican free-tailed bats.

Since 1936, the size of the summer population of Mexican free-tailed bats, Tadarida brasiliensisat Carlsbad Caverns, New Mexico, declined from an estimated 8.7 million to 700,000 in 1991. This decline has been attributed primarily to human disturbance and the heavy agricultural use of organochlorine pesticides. Members of this species forage extensively over heavily agricultural areas, feeding on insects potentially contaminated with high levels of insecticides and trace metals. However, contamination from elements such as lead, cadmium, and arsenic have not been examined. The accumulation of these elements in wild vertebrates is often a primary reflection of contamination of the food supply. The presence of elemental contaminants in body tissues of bats is poorly documented. The objectives of this study were to examine and compare lead, cadmium, and arsenic contamination in livers of adult T. Brasiliensis from Carlsbad Caverns and Vickery Cave, a maternity colony in northwestern Oklahoma. Lead, cadmium, and arsenic were specifically selected because of their documented toxic and/or reproductive effects and their potential availability to this species. Large quantities of tetraethyl lead have been released into the environment and other lead compounds continue to be released by industrial manufacturing and petroleum refinement processes. Cadmium is used in amore » number of industrial processes such as metal plating and fabrication of alloys and is released from phosphate fertilizers and combusted coals. Teratogenicity appears to be greater for cadmium than for other elements. Arsenical compounds have been commonly used as herbicides and defoliants. These compounds have been demonstrated to cause abnormal embryonic development, degenerative tissue changes, cancer, chromosomal damage, and death in domestic animals.« less

Clonal diversity in overwintering populations ofSchizaphis graminum(Homoptera: Aphididae)

AbstractThe intergenic spacer region of the rRNA cistron was used as a molecular fingerprinting probe to study clonal diversity inSchizaphis graminum(Rondani). A high degree of clonal diversity was found in overwintering populations on wheat from Kansas, Texas and Oklahoma. Out of 184 individuals tested, 132 unique maternal lineages wereidentified. Overall, clonal diversity of overwintering populations was no less than in spring and summer populations. However, in some fields there were more instances where individuals of the same genotype were identified. By partitioning the total population diversity into various sampling components (fields, counties and states), 93.1% of the total diversity was found among individualS. graminumwithin fields. Overwintering of many genetically distinct clones as parthenogenetic morphs is one mechanism by which clonal diversity is maintained in populations ofS. graminum. The incidence of clonal diversity further substantiates the importance of theS. graminumholocycle for generating genetic heterogeneity in the USA.