Breeding in the stable boreal landscape: lake habitat variability drives brood production in the teal (Anas crecca)

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Native brook trout and invasive rainbow trout respond differently to seasonal weather variation: Spawning timing matters

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Effects of host abundance on larch budmoth outbreaks in the European Alps

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A review of the population dynamics of mule deer and black‐tailed deer Odocoileus hemionus in North America

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Population suppression for control of the blowfly Lucilia sericata and sheep blowfly strike

Abstract.

• 1 The control of ovine myiasis by suppression of populations of the blowfly Lucifia sericata was investigated experimentally on three farms in the south-west of England in 1992 and 1993.
• 2 In blind trials, sheep on one farm (control) were given two doses of placebo, on a second two doses of the larvicide cyromazine (Vetrazin®, CibaGeigy), and on a third cyromazine and a subsequent dose of placebo.
• 3 The first treatment was given shortly before the predicted spring emergence of L.sericata and the second shortly before the predicted emergence of the second generation. Previous simulation analysis had identified strategic early-season treatment as the optimum for blowfly population suppression.
• 4 On both treatment farms significantly smaller L.sericata populations were recorded throughout 1992 and the incidence of strike was significantly lower than on the control farm. The results show that appropriate early-season timing of sheep treatment can suppress populations of L.sericata and could be used by farmers to reduce the incidence of blowfly strike.
• 5 The results suggest, however, that the effectiveness of population suppression and strike incidence may have been influenced by immigration into the control areas and by adverse weather, the latter changing the susceptibility of sheep to strike and resulting in rising strike incidence even when L.sericata population densities were low. In practice, therefore, blowfly population suppression should be employed as a component of an integrated strike management programme.

     

Extreme climatic events affect populations of Asian chestnut gall wasps,Dryocosmus kuriphilus,but do not stop the spread

1. Global climate change affects the frequency of extreme weather events that can influence plant–insect interactions.
2. We evaluated how the late-spring frost and severe drought that occurred in Spain in 2017 affected interactions between the invasive gall insect, Dryocosmus kuriphilus, and the native tree, Castanea sativa. We assessed effects on insect survival, fertility, population growth, and effects through changes in tree palatability and in other pests and pathogens.
3. Late-spring frost reduced D. kuriphilus to 25–40% of previous abundance. Wasp populations recovered rapidly (>7-fold in 3 years), consistent with density-dependence in population dynamics.
4. Larvae affected by freeze or drought were smaller. Female fecundity was affected by the freeze 1 year later.
5. Late-spring frosts and severe drought affected leaf size and physiology. Water content was higher within galls, but nitrogen was higher within galls in non-freeze plots after weather conditions improved.
6. Freezing also influenced the secondary chemistry of leaves. Phenol concentrations were lower, and terpenes higher, in frozen plots, while condensed tannins remained the same. Condensed tannins were reduced to half in the drought year.
7. Freezing had limited effects on damage from other pests and pathogens.
8. Our work expands understanding of how climate and weather affects forest pests.

     

Translocations maintain genetic diversity and increase connectivity in sea otters,Enhydra lutris

Sea otters, Enhydra lutris, were once abundant along the nearshore areas of the North Pacific. The international maritime fur trade that ended in 1911 left 13 small remnant populations with low genetic diversity. Subsequent translocations into previously occupied habitat resulted in several reintroduced populations along the coast of North America. We sampled sea otters between 2008 and 2011 throughout much of their current range and used 19 nuclear microsatellite markers to evaluate genetic diversity, population structure, and connectivity between remnant and reintroduced populations. Average genetic diversity within populations was similar: observed heterozygosity 0.55 and 0.53, expected heterozygosity 0.56 and 0.52, unbiased expected heterozygosity 0.57 and 0.52, for reintroduced and remnant populations, respectively. Sea otter population structure was greatest between the Northern and Southern sea otters with further structuring in Northern sea otters into Western, Central, and Southeast populations (including the reintroduced populations). Migrant analyses suggest the successful reintroductions and growth of remnant groups have enhanced connectivity and gene flow between populations throughout many of the sampled Northern populations. We recommend that future management actions for the Southern sea otter focus on future reintroductions to fill the gap between the California and Washington populations ultimately restoring gene flow to the isolated California population.     

Optimizing biocontrol using phenological day degree models: the European earwig in pipfruit orchards

• 1 Phenological day degree models are often used as warning systems for the emergence of arthropod pests in agricultural crops or the occurrence of natural enemies of the pest species. In the present study, we report on a case study of the European earwig Forficula auricularia L., which is an important natural enemy in pipfruit orchards, and describe how such a day degree model can be used to avoid negative effects of crucial orchard management, such as spray applications and soil tillage. A precise timing of these interventions in relation to the phenology of natural enemies will enhance biocontrol.
• 2 Earwig population dynamics are characterized by single‐ and double‐brood populations, each with specific biological characteristics.
• 3 A day degree model capable of predicting the phenology of local earwig populations of both population types was developed. The model was checked for accuracy by comparing the first field observation dates of various life stages with predicted values using temperature data from the nearest weather station. In addition, variation in development time was assessed using field data.
• 4 The model was able to make predictions on a global scale. Although single‐ and double‐brood populations differ in phenology, the predictions of first appearance dates were similar. Variation in development time showed that single‐brood populations were more synchronized.
• 5 Our phenological model provides an accurate tool for predicting and simulating earwig population dynamics, as well as for enhancing the biocontrol of pests in pipfruit orchards.

     

Defining evolutionary boundaries across parapatric ecomorphs of Black Salamanders (Aneides flavipunctatus) with conservation implications

The accurate delimitation of evolutionary population units represents an important component in phylogeographic and conservation genetic studies. Here, we used a combined population assignment and historical demographic approach to study a complex of ecomorphologically distinctive populations of Black Salamanders (Aneides flavipunctatus) that are parapatrically distributed and meet at a three‐way contact zone in north‐western California. We used mitochondrial tree‐based and multilocus clustering methods to evaluate a priori two‐ (Northern and Southern) and three (Northern, Coast and Inland) population hypotheses derived from previous studies. Mitochondrial results were consistent with the two‐ and three‐population hypotheses, while the nDNA clustering results supported only the two‐population hypothesis. Historical demographic analyses and mtDNA gene divergence estimates revealed that the Northern and Southern populations split during the Pliocene (2–5 Ma). Subdivision of the Southern population into Coast and Inland populations was estimated to be late Pleistocene (0.24 Ma), although our mtDNA results suggested a Pliocene divergence. Effective gene flow estimates (2N_em) suggest that either the two‐ or three‐population hypotheses remain valid. However, our results unexpectedly revealed that the Northern population might instead represent two parapatric populations that separated nearly 4 Ma. These results are surprising because the Pliocene divergence between these ecomorphologically conservative forms is similar or older than for the ecomorphologically divergent Coast and Inland sister populations. We conclude that Black Salamanders in north‐western California belong to at least three or four populations or species, and these all meet criteria for being Evolutionary Significant Units or ‘ESUs’ and therefore warrant conservation consideration.     

Seasonal and spatial population loads of a tropical insect: the case of the coffee leaf-miner in Mexico

Abstract.

• 1 The effect of weather fluctuations in a tropical rain forest upon a leaf-miner (the coffee leaf-miner Leucoptera coffeella Guerin-Meneville (Lepidoptera: Lyonetiidae)) was studied in Veracruz, Mexico. The combined effect of temperature and precipitation upon the leaf-miner populations was investigated in coffee plantations located along an elevation transect and throughout the annual seasons. The effect of plant diversity, displayed by the presence or absence of shade trees in coffee plantations, upon the population loads of the leaf-miner was also investigated.
• 2 The leaf-miner population increased significantly during the period of intermediate temperature and low precipitation (spring season). Elevation also affected the population load of the insect: leaf-miner populations were larger at low elevations (where temperatures are high and precipitation low) than at high elevations.
• 3 Plant structural diversity did not affect the population loads of the leaf-miner.
• 4 The results indicate that the direct and indirect effects of temperature and precipitation are significant factors in the population dynamics of the coffee leafminer. It is suggested that even moderate fluctuations in climatic conditions in tropical and subtropical regions may also play an important role in the dynamics of tropical insect populations, similar to that found in temperate zones where climatic fluctuations are extreme.

     

Range expansion of the small spruce bark beetle Ips amitinus: a newcomer in northern Europe

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Interspecific competition between insect herbivores: asymmetric competition between cinnabar moth and the ragwort seed-head fly

ABSTRACT.

• 1 Removal field experiments and observational studies have been undertaken to determine whether feeding by cinnabar moth Tyria jacobaeae L. on the flower heads of ragwort Senecio jacobaea L. affects the abundance of the fly Pegohylemyia seneciella (Meade) that feeds in the flower heads as a larva.
• 2 Correlations between the population density of cinnabar moth and the population density of the fly were suggestive of habitat separation, but provided little evidence of exploitation competition.
• 3 Removal of cinnabar moth by hand from replicated plots over two years shows that, in years when ragwort flower production is consumed by cinnabar moth caterpillars, the fly may show no recruitment at all.
• 4 Fly populations persist in refugia, exploiting ragwort plants that grow in areas where there are no cinnabar moth.
• 5 Recruitment of ragwort is not seed limited, so the reduction in seed production caused by P. seneciella (maximum about 30%) has no impact on ragwort abundance, or on the abundance of cinnabar moth.
• 6 We conclude that there is strong interspecific competition between these two species, and that the competition is highly asymmetric. The cinnabar moth had a substantial effect on the recruitment of the fly in 1986, but the fly has no measurable impact on the recruitment of the moth. In six years out of seven in our long-term study, cinnabar moth reduced flower production to levels comparable to those measured in 1986, and we infer that strong competition with the fly was likely in six years out of seven.
• 7 One reason why there are so few published examples of asymmetric interspecific competition may be simply that the experiments are thought too obvious to be worth doing. We argue that this is not a good reason for eschewing manipulative field experiments, and that few processes in ecology are at all obvious when investigated in detail.

     

Analysis of population genetic structure of two closely related tortricid species of economic importance on macadamias and litchis in South Africa

Abstract

• 1 The macadamia nut borer Thaumatotibia (Cryptophlebia) batrachopa and the litchi moth Cryptophlebia peltastica are Afrotropical species causing extensive damage to cultivated macadamias and litchis in the northernmost provinces in South Africa. Cryptophlebia peltastica also occurs as natural populations throughout the country.
• 2 To analyse the population genetic structure of the two species, amplified fragment length polymorphism analysis was conducted. Patterns of genetic diversity in C. peltastica populations in the Mpumalanga province, where the species is controlled, were compared with those in the Western Cape, where populations occur under natural conditions.
• 3 Gene diversity was high within T. batrachopa populations (H = 0.2219) with significant genetic differentiation among populations (G_st = 0.358). Cluster analysis showed that geographical populations were closely related and extensive divergence was found over local scales.
• 4 Similar to that of T. batrachopa, genetic diversity and population differentiation was high within both C. peltastica Mpumalanga and Western Cape populations (H = 0.1906 and 0.1687 and G_st = 0.4124 and 0.3799, respectively).
• 5 It is suggested that the population genetic structure of both species is influenced by their limited ability to disperse. In addition, chemical control of C. peltastica in the Mpumalanga province has not succeeded in reducing the population size, but the C. peltastica population subdivision in the Western Cape may be influenced by the limited distribution of host plants in this region.

     

Local and landscape scale drivers of Euschistus servus and Lygus lineolaris in North Carolina small grain agroecosystems

1. Crop production sequences influence arthropod populations in temporally unstable row crop systems. Winter wheat (Triticum aestivum L.) represents one of the earliest abundant crops in south-eastern United States. This study aims to understand primary source habitats driving brown stink bug, Euschistus servus (Say), and tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), population abundance in wheat.
2. To better understand these relationships, adult and nymphal densities were in wheat fields weekly from flowering through harvest in 2019 and 2020. Geospatial data were used to measure landscape composition surrounding sampled fields. We investigated the influence of landscape predictors on E. servus and L. lineolaris abundance using generalized linear mixed modelling.
3. Field size, proportion of agriculture, proportion of wheat area, and proportion of soybean Glycine max L.) area from the previous year in the surrounding landscape were associated with E. servus abundance in wheat. Similarly, L. lineolaris abundance was associated with proportion of wheat area and soybean area from the previous year.
4. These results reveal the influence of soybean area planted the previous year on insect pest densities the following spring in wheat. Further, results suggest agricultural landscapes dominated by wheat are associated with decreased pest abundance across the sampled region.

     

Habitat loss and degradation due to farming intensification modify the floral visitor assemblages of a semiarid keystone shrub

1. The expansion of intensive agriculture has severely altered landscapes, a process that has been aggravated by the increase of greenhouse agriculture. However, few studies have considered the combined effects of habitat loss/degradation and greenhouse farming on insect visitors to native plants.
2. We analysed how habitat loss/degradation and greenhouse farming are related to the composition, abundance, and richness of the insect assemblages visiting flowers in a semiarid keystone shrub (Ziziphus lotus) in southeast Spain, home to Europe's largest area of greenhouses. We studied 21 populations distributed across a gradient of greenhouse intensification and habitat loss.
3. The composition, abundance, and richness of the Ziziphus insect assemblage substantially varied between populations and were differently affected by natural habitat-remnant and landscape degradation and population isolation.
4. Insect abundance was negatively affected by habitat loss at population level but positively affected at individual Ziziphus scale. Honey-bee relative abundance increased in highly degraded landscapes and isolated populations, being positively associated with hoverflies and negatively with ants and bee-flies. Wild bees, carrion flies, and wasps remain neutral along the degradation axes. Insect visitor abundance per plant affected positively the flower visitation rate, which was also favoured by the relative abundance of honey bees, wild bees, and hoverflies. Species richness was not influenced by anthropogenic degradation, and did not affect flower visitation rate.
5. Our results highlight the fragility of wild pollinator communities to landscape and habitat degradation, and the need to regulate intensive farming practices to preserve wild insect pollinator assemblages in semiarid habitats.

     

Seasonal temperature and precipitation regulate brook trout young‐of‐the‐year abundance and population dynamics

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A new experimental approach to investigate migration in Pieris brassicae L.

Abstract.

• 1 It is possible to correlate distinct sequences of flight behaviour in caged females of the migrant butterfly Pieris brassicae with the main flight direction of released individuals of the same stock. The attempts to escape out of the cage point to the same mean direction as the flights of the released butterflies. This provides an experimental tool to investigate some unsolved questions concerning migration behaviour.
• 2 This study examines the constancy of the flight direction of a group of butterflies, the specificity of the direction in two populations of different geographical origin, and the frequently reported change in flight direction of subsequent generations.
• 3 The results indicate that the main flight direction of a tested group is very constant during 2 days of observation. Different directions have been detected in populations originating from Northern Germany and Southern France, respectively. The preferred directions are discussed as an adaptation to the geographical circumstances. Subsequent generations of the population from Northern Germany also show different directions. The spring generation flies to the north, the autumn generation in the opposite direction. This result corresponds to field observations that in P.brassicae a return flight occurs in subsequent generations of a year.

     

Sex‐skewed trophic impacts in ephemeral wetlands

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Prospective analysis of the invasive potential of the European grapevine moth Lobesia botrana (Den. & Schiff.) in California

• 1 The polyphagous European grapevine moth Lobesia botrana (Den. & Schiff.) is the principal native pest of grape berries in the Palearctic region. It was found in Napa County, California, in 2009, and it has subsequently been recorded in an additional nine counties, despite an ongoing eradication programme. The present study aimed to assess prospectively its potential geographical distribution and relative abundance in California and the continental U.S.A. A subsidiary goal was to provide explanation for timing control measures.
• 2 Data from the European literature were used to formulate and parameterize a holistic physiologically‐based demographic model for L. botrana. This model was linked to an extant mechanistic model of grapevine phenology, growth and development that provides the bottom‐up effects of fruiting phenology, age and abundance on L. botrana dynamics. Fruit age affects larval developmental rates, and has carryover effects on pupal development and adult fecundity. Also included in the model were the effects of temperature on developmental, survival and fecundity rates.
• 3 Observed daily weather data were used to simulate the potential distribution of the moth in California, and the continental U.S.A. The relative total number of pupae per vine per year was used as the metric of favourability at all locations. The simulation data were mapped using grass gis ( http://grass.osgeo.org/ ).
• 4 The model predicts L. botrana can spread statewide with the highest populations expected in the hotter regions of southern California and the lower half of the Central Valley. In the U.S.A., areas of highest favourability include south Texas, and much of the southeast U.S.A.
• 5 The effects of a warmer climate on pest abundance were explored by increasing observed mean temperatures 2° and 3 °C. L. botrana abundance is expected to increase in northern California and in the agriculturally rich Central Valley but to decrease in the hot deserts of southern California where summer temperatures would approach its upper thermal limit.
• 6 Analysis of the timing of mating disruption pheromone for control of L. botrana suggests the greatest benefit would accrue by targeting adults emerging from winter diapause pupae and the flight of first summer adults.

     

Spatio‐temporal variation in Helicoverpa egg parasitism by Trichogramma in a tropical Bt‐transgenic cotton landscape

• 1 Understanding the spatio‐temporal dynamics of insects in agroecosystems is crucial when developing effective management strategies that emphasize the biological control of pests.
• 2 Wild populations of Trichogramma Westwood egg parasitoids are utilized for the biological suppression of the potentially resistant pest species Helicoverpa armigera (Hübner) in Bt‐transgenic cotton Gossypium hirsutum L. crops in the Ord River Irrigation Area (ORIA), Western Australia, Australia.
• 3 Extensive, spatially‐stratified sampling during a season of relatively high Trichogramma abundance found that spatial patterns of pest egg parasitism in the ORIA tend toward heterogeneity, and do not necessarily coincide with host spatio‐temporal dynamics. Both patterns of host egg density and mean rates of parasitism are not good indicators of parasitoid spatio‐temporal dynamics in ORIA cotton crops.
• 4 Parasitism rates can be significantly higher within the middle strata of the cotton plant canopy before complete canopy closure, despite a similar number of host eggs being available elsewhere in the plant.
• 5 Spatial variation in egg parasitism by Trichogramma in Bt‐transgenic cotton is evident at the between‐field, within‐field and within‐plant scale, and is not solely driven by host spatial dynamics. These factors should be considered when estimating Trichogramma impact on pest species during biological control and spatio‐temporal studies of host‐parasitoid interactions in general.