Adult Density Research Articles

Evaluation of water depth and inundation duration on Typha domingensis sustainability in the Everglades Stormwater treatment areas: A test cell study

Typha domingensis is a dominant plant species in the Everglades Stormwater Treatment Areas, freshwater wetlands constructed to reduce phosphorus (P) levels in stormwater runoff prior to discharge into the Everglades. Water depth and duration of inundation can negatively affect the health of these plants. To determine the effect of water depth and inundation duration, Typha plants were grown in this study in a series of 15 test cells, 0.2 ha in area, and exposed to five water-depth treatments over 10 months: control (40 cm), shallow (61 cm), moderate (84 cm), deep (104 cm) and extremely deep (124 cm). Mean adult Typha densities declined from 14.1 shoots m−2 in the control to 10.9 and 10.5 shoots m−2 in the deep and extremely-deep treatments, respectively. However, only mean juvenile Typha densities were significantly different among water-level treatments, declining from 3.2 juveniles m−2 in the control to 1.2 and 0.6 juveniles m−2 in the deep and extremely-deep treatments, respectively. Typha leaf elongation rate (LER) was significantly higher in the deeper treatments, with the highest rates measured during the active growing season (July to October). LER increased from 6.84 cm day−1 during June baseline measurements to 8.89 cm day−1 in the deeper treatments after eight weeks of continuous inundation. Typha showed morphological plasticity to adapt to deep water through changes in morphology and biomass allocation. Typha grew significantly taller and heavier to adapt to deep-water conditions and facilitate gas exchange between the above and belowground tissues. Ramet height of Typha harvested at the end of the study averaged 343 and 374 cm in the deep and extremely-deep treatments, respectively, compared to 285 cm in the control. Likewise, the weight of individual adult ramets was significantly greater in the deeper treatments (256 g ramet−1) compared to the control (123 g ramet−1). Although none of the water-level treatments resulted in a total collapse of their Typha populations, increased LER in the deeper treatments resulted in less structural support in stems, causing substantial Typha lodging when water levels were lowered at the end of the study. These findings provide valuable insight into the effect of different water-level inundations on plant responses and overall health of Typha populations in the STAs.

California Sea Cucumber (Apostichopus californicus) Abundance and Movement on a Commercial Shellfish Aquaculture Farm

California sea cucumbers (Apostichopus californicus) are often abundant at oyster farms in British Columbia, Canada both on the suspended gear as juveniles and on the seafloor beneath them as a mixture of juveniles and adults. Their natural abundance, high value, and potential to mitigate benthic organic loading has led to an interest in their coculture with oysters. Whether farmed sea cucumbers ought to be contained to physically separate them from wild stocks is debated. The present three-year field study examined the movement of wild California sea cucumbers on/off an operational oyster farm (~3000 m2) to help inform future sea cucumber aquaculture development. Sea cucumber effects on organic loading, immigration to/emigration from the farm, and the efficacy of various containment-material mesh types and sizes were examined. Juvenile and adult sea cucumber densities on the farm steadily increased from the end of winter through the end of summer, likely due in large part to juveniles falling off the suspended oyster gear, which occurred at an average rate of ~780 ind d−1 (for the whole farm) in the summer months. The largest increase in abundance on the farm was observed between January and March/April, when the population increased by 100–350 ind d−1. Between late summer and early winter, sea cucumbers emigrated from the farm at a rate of 50–90 ind d−1, neither juvenile nor adult densities on the farm changing appreciably over the winter. The sea cucumber density showed a progressive decrease in the first 20 m from the farm, after which the animals were scarcely noticed. Apostichopus californicus did not significantly decrease sediment organics beneath the farm compared to a nearby control site, but such an effect may have been lost due to their seasonal feeding cycles and/or the presence of other benthic grazers that were not part of our exclusion trial. Overall, our findings suggest that the separation of farmed and wild California sea cucumbers on a shellfish farm can only be guaranteed through containment, given the dynamic immigration and emigration patterns of wild stocks. Through laboratory trials, we found that individuals of A. californicus were able to squeeze through mesh as small as 32% of their contracted width and could escape fenced areas (90 ± 4% escape from nylon fencing and 40 ± 8% escape from VexarTM fencing) unless the fencing extended above the water surface (where there was no escape from either type).

Density effects on a tropical copepod Acartia sp.: Implications as live feed in aquaculture

AbstractCalanoid copepods Acartia species are major live feeds for the early stages of economically important marine fish in hatcheries in Southeast Asian countries. However, rearing Acartia copepods at high densities to increase productivity remains a major challenge. To address the issue, we conducted two experiments on (1) Acartia sp. nauplii (1000, 3000, 6000, 9000, 12,000, and 15,000 individuals L−1) and (2) adults (1000, 1500, 2000, and 2500 individuals L−1). We assessed key parameters for biomass production: development, survival, and egg and nauplii production. In general, increased density resulted in longer development time, lowered survival and egg and nauplii production but did not affect the size of adult males and females. Despite survival to adulthood decreasing at higher stocking nauplii densities, the number of surviving adults was highest at a stocking density of 12,000 individuals L−1. Egg and nauplii production was very low which may be the result of high predation. The total eggs and nauplii harvested were highest at the lowest adult density. These results are essential for the biomass production of Acartia sp. in central Vietnam.

Effect of Foliar Fertilization with Potassium Silicate on some Morphological Characters of Strawberry Leaves Reducing Sucking Insects

The results showed that foliar fertilization with potassium silicate had a clear effect on increasing the thickness of the upper and lower epidermal cuticle layer and increased the thickness of the leaf, as the thickness after the first spray of the upper epidermal cuticle reached 22 microns and the lower epidermal cuticle 11 microns, and the leaf thickness reached 194.8 microns. As for after the second spray, the thickness of the leaf and the upper and lower cuticle layer reached 198.66, 25.33, 16.66 microns, and the third spray was characterized by an increase in the thickness of the leaf compared to the first and second spray, as the thickness of the leaf reached 206.66 microns, and the upper and lower cuticle epidermis was 28.33 and 19 microns, respectively. Compared with the control, the thickness of the paper was 190 microns, and the upper and lower epidermal cuticle layers were 10 and 20 microns, respectively. The results of the study indicated that the treatment of foliar fertilization with silicates with three sprays was superior in reducing the population density of whitefly and aphids on strawberry plant Mergent variety. The effect of the three sprays on the average number of Bemisia tabaci nymphs was 1.16 nymphs / leaf, the first spray had 6.66 nymphs / leaf, and the second spray had 19.66 nymphs / leaf. The effect of the three sprays on nymphs and adults of Aphis gossypii was 0.36 nymphs/leaf and 0.27 adults/leaf. For the second spray, the effect was on nymphs at a rate of 2.33 nymphs/leaf, and on adults at a rate of 1.91 adults/leaf. The first spray had the least effect on reducing the population density, as it reached nymphs at a rate of 8.16 nymphs/leaf. And for adults, 6.33 adults / leaf, with clear significant differences. As for the effect of three sprays of potassium silicate on the numerical density of nymphs and adults of Aphis fabae, the rate of nymphs reached 0.33 nymphs / leaf after the third spray, and for adults, at a rate of 0.27 adults / leaf, which is the most effective compared to the first and second sprays. The average numerical density of nymphs was 9.08 nymphs/leaf and for adults 5.24 adults/leaf after the first spray, while after the second spray the average density was 4.30 nymphs/leaf and for adults 2.16 adults/leaf.

Planktonic Duration of the Bryozoan Cyphonautes Larva and Limits on Growth Rate Imposed by Its Form-Limited Maximum Clearance Rate.

AbstractThe form of the cyphonautes larva of bryozoans changes little during development. The ciliated band that generates the feeding current increases nearly in proportion to body length, so that the maximum rate of clearing planktonic food from a volume of water becomes increasingly low relative to body protein. This development is unlike the other larvae that produce a feeding current with bands of simple cilia. The cyphonautes' growth rate has therefore been predicted to be unusually low when food is scarce. As predicted, cyphonautes larvae of a species of Membranipora starved at concentrations of food that supported growth of pluteus larvae. Comparisons between the cyphonautes and plutei of a sand dollar were for growth from first feeding to metamorphosis, with a mix of two algal species. Another comparison was for growth of cyphonautes at an advanced stage and plutei of a regular sea urchin at an early stage, with food in seawater at a reduced concentration. The low maximum clearance rate did not prevent rapid growth and development of some cyphonautes from egg through metamorphosis when food was abundant. Twenty-nine days for development to metamorphosis in the laboratory with abundant food was close to Yoshioka's estimate of larval duration from the time lag between adult zooid density and larval abundance in a population in the Southern California Bight. Despite individual variation in growth rates and other physiological and environmental influences, simple measures of larval form predicted the differences in larval performance: scarce food extended larval duration for the cyphonautes more than for plutei.

Gill net catchability of walleye (Sander vitreus): Are provincial standards suitable for estimating adult density outside the region?

Standard gill netting protocols are increasingly used to assess freshwater fish populations. Understanding the catchability (q) of fish following these protocols enables direct estimation of density, which has advantages over relative abundance from analytical and applied research perspectives. However, catchability is complex. The application of q estimated in one region may be inappropriate for another if physical and biological processes driving catchability differ. Cross-region assessments of q are needed to assess the applicability of estimates over a broader geographic and environmental range. In this study, we evaluated whether the global estimate of q (1.044 ha/gang; variance = 0.2268) derived by Giacomini et al. (2020) for walleye Sander vitreus ≥ 350 mm total length (TL) was suitable for application in two Colorado, USA reservoirs supporting recreational fisheries and wild spawn operations. We followed provincial standards in Ontario and Quebec, Canada (i.e., Fall Walleye Index Netting) combined with other corrections for size-dependent catchability to estimate the density of mature, adult walleye ≥ 470 mm TL for comparison to independent estimates from mark-recapture analyses. Following similar methodologies, we found that the global estimate of q combined with size-dependent gill net retention coefficients underestimated the density of adults by nearly 80%, but uncertainty in point estimates can be high. Results highlighted the need to better understand sources of uncertainty, including factors influencing size-dependence in gill net encounter when extending estimates of q to other size classes of fish, systems, and regions. Estimates of catchability for large-bodied adult walleye in our systems were consistent, but relatively low, ranging from 0.203 ha/gang (95% confidence limits = 0.133–0.298) to 0.227 ha/gang (0.091–0.556). We expand the geographic and environmental range of paired mark-recapture and gill net Catch Per Unit Effort information and discuss potential factors contributing variability to estimates of catchability for adult walleye.

Temporal and spatial factors influencing Systena frontalis (Coleoptera: Chrysomelidae) behavior in Virginia nurseries.

Ornamental plant production in eastern Virginia nurseries have been greatly impacted by Systena frontalis (F.), also known as the red-headed flea beetle. With the advent of S. frontalis as a prevalent pest in the past 2 decades, baseline phenology and behavior are currently understudied within Virginia nurseries. This pest is costly to control due to insecticide expenses and loss of saleable plants. In 2021 and 2022, populations of this insect were monitored at 2 commercial nurseries in eastern Virginia in order to better understand their temporal and spatial population dynamics. Patterns that emerged indicated S. frontalis could have up to 3 generations in eastern Virginia, with peaks of adult abundance in June, late July, and late August to early September. Phenylethyl alcohol was tested as an adult attractant lure, but it was found to be ineffective under nursery conditions. Diel monitoring demonstrated these adults were most active from 1100 to 1500 h. Severity of defoliation at the leaf level increased linearly with increased density of adults, where 5 individuals defoliated up to 4% of any Hydrangea paniculata cv. 'Limelight' leaf in 1 wk under greenhouse conditions. Timing of scouting and insecticide sprays according to the adult activity peaks of the day and across the season may allow reduction in overall insecticide usage.

When the population of an endangered marine mollusc (Patella ferruginea) increases almost three-fold in ten years. Reality or fiction?

The critically endangered species Patella ferruginea (Gastropoda, Patellidae), endemic to the western Mediterranean, has breeding populations in both natural and artificial habitats, the latter of which are generally linked to port infrastructures. Over the past decade, the temporal change of this species’ population has been monitored (structure and density) using exhaustive censuses along Ceuta’s coast (Strait of Gibraltar), one of the few stronghold populations within the entire Mediterranean basin. This study focuses on the population dynamics of P. ferruginea in Ceuta and the environmental factors that affect the structure of this population, such as wave exposure, coastline heterogeneity, substratum roughness, substratum lithology, and chlorophyll-a concentration. Different potential negative interactions were also considered: angling, shell fishing, bathing in the intertidal, bathing near the intertidal, recreational boating and temporary migrant campsites nearby. The results have shown in the period 2011-2021, the estimated size of P. ferruginea population has increased by 200 %, from 55,902 to 168,463 individuals (of which 131,776 are adults). The subpopulation with the greatest increase in these years was the one settled on dolomitic rip-raps inside the Ceuta’s harbor, with an increase of 1,288%. The results of the present study indicate that Ceuta hosts the main population of this endangered species through its distributional range (Western Mediterranean), being a source population on the Southern Iberian Peninsula that its preservation must be prioritized. Statistical modelling has shown that the adult density of P. ferruginea is positively influenced by coastal heterogeneity, habitat area and substratum roughness, but negatively by vertical inclination, concentration of chlorophyll-a, and anthropogenic impact. These results also support the concept of ¨Artificial Marine Micro-Reserves¨ as a new area-based conservation measure according with the IUCN guidelines, as these will contribute to setting up a network of these source populations that promote genetic flow among populations, with eventual recolonization throughout its original distribution.

Short‐term effects on Unionid mussel density and distribution before and after low‐head dam removal in northern New York

AbstractUnionid mussel populations have declined in many environments, particularly those that were altered by human activities such as dam construction and removal. The Fort Covington Dam blocked the Salmon River in northern New York upriver of its confluence with a smaller tributary, the Little Salmon River. This dam was removed in 2009. My study compared the mean ranked density of mussels in both rivers for the pre‐removal period (2005–2008) to the post‐removal period (2009–2012) with special attention to Lampsilis cariosa and Margaritifera margaritifera. Systematic sampling was used at six riffles and double sampling at four glides divided between the Salmon and Little Salmon rivers from 2005 through 2012. The Little Salmon River served as a control. Mean ranked adult mussel density was not significantly different between the two rivers in the pre‐removal period but was significantly greater in the Little Salmon River after dam removal. Living mussels of 13 species were collected dominated by Elliptio complanata. Dam removal did not affect sediment sorting, porosity, water chemistry, or mussel species distribution. Rapid dewatering of the reservoir led to stranding and death of mussels in the reservoir and in the adjacent ponds. Increased water velocity, exacerbated by rain, mobilized sediment that buried a potentially large mussel bed downstream of the dam where Lampsilis cardium and L. cariosa were abundant, which showed little recovery by 2013.

Immigration and seasonal bottlenecks: high inbreeding despite high genetic diversity in an oscillating population of Culicoides sonorensis (Diptera: Ceratopogonidae).

Most population genetic studies concern spatial genetic differentiation, but far fewer aim at analyzing the temporal genetic changes that occur within populations. Vector species, including mosquitoes and biting midges, are often characterized by oscillating adult population densities, which may affect their dispersal, selection, and genetic diversity over time. Here, we used a population of Culicoides sonorensis from a single site in California to investigate short-term (intra-annual) and long-term (inter-annual) temporal variation in genetic diversity over a 3 yr period. This biting midge species is the primary vector of several viruses affecting both wildlife and livestock, thus a better understanding of the population dynamics of this species can help inform epidemiological studies. We found no significant genetic differentiation between months or years, and no correlation between adult populations and the inbreeding coefficient (FIS). However, we show that repeated periods of low adult abundance during cooler winter months resulted in recurring bottleneck events. Interestingly, we also found a high number of private and rare alleles, which suggests both a large, stable population, as well as a constant influx of migrants from nearby populations. Overall, we showed that the high number of migrants maintains a high level of genetic diversity by introducing new alleles, while this increased diversity is counterbalanced by recurrent bottleneck events potentially purging unfit alleles each year. These results highlight the temporal influences on population structure and genetic diversity in C. sonorensis and provide insight into factors effecting genetic variation that may occur in other vector species with fluctuating populations.

Effects of Madagascar marine reserves on juvenile and adult coral abundance, and the implication for population regulation

Recruitment is a critical component in the dynamics of coral assemblages, and a key question is to determine the degree to which spatial heterogeneity of adults is influenced by pre-vs. post-settlement processes. We analyzed the density of juvenile and adult corals among 18 stations located at three regions around Madagascar, and examined the effects of Marine Protected Areas (MPAs). Our survey did not detect a positive effect of MPAs on juveniles, except for Porites at the study scale. The MPA effect was more pronounced for adults, notably for Acropora, Montipora, Seriatopora, and Porites at the regional scale. For most dominant genera, densities of juveniles and adults were positively correlated at the study scale, and at least at one of the three regions. These outcomes suggest recruitment-limitation relationships for several coral taxa, although differences in post-settlement events may be sufficiently strong to distort the pattern established at settlement for other populations. The modest benefits of MPAs on the density of juvenile corals demonstrated here argue in favor of strengthening conservation measures more specifically focused to protect recruitment processes.

A Glucocorticoid-Sensitive Hippocampal Gene Network Moderates the Impact of Early-Life Adversity on Mental Health Outcomes

BackgroundEarly stress increases the risk for psychiatric disorders. Glucocorticoids are stress mediators that regulate transcriptional activity and morphology in the hippocampus, which is implicated in the pathophysiology of multiple psychiatric conditions. We aimed to establish the relevance of hippocampal glucocorticoid-induced transcriptional activity as a mediator of the effects of early life on later psychopathology in humans. MethodsRNA sequencing was performed with anterior and posterior hippocampal dentate gyrus from adult female macaques (n = 12/group) that were chronically treated with betamethasone (glucocorticoid receptor agonist) or vehicle. Coexpression network analysis identified a preserved gene network in the posterior hippocampal dentate gyrus that was strongly associated with glucocorticoid exposure. The single nucleotide polymorphisms in the genes in this network were used to create an expression-based polygenic score in humans. ResultsThe expression-based polygenic score significantly moderated the association between early adversity and psychotic disorders in adulthood (UK Biobank, women, n = 44,519) and on child peer relations (ALSPAC [Avon Longitudinal Study of Parents and Children], girls, n = 1666 for 9-year-olds and n = 1594 for 11-year-olds), an endophenotype for later psychosis. Analyses revealed that this network was enriched for glucocorticoid-induced epigenetic remodeling in human hippocampal cells. We also found a significant association between single nucleotide polymorphisms from the expression-based polygenic score and adult brain gray matter density. ConclusionsWe provide an approach for the use of transcriptomic data from animal models together with human data to study the impact of environmental influences on mental health. The results are consistent with the hypothesis that hippocampal glucocorticoid-related transcriptional activity mediates the effects of early adversity on neural mechanisms implicated in psychiatric disorders.

Effect of <i>In Vitro</i> Culture and Embryo Transfer on Neuronal Density and Neurogenesis in the Brain of C57BL/6J Mice

The current research is aimed to determine the long-term effects of the in vitro culture (IVC) and embryo transfer (ET) on the neonatal offspring development, as well as on the adult hippocampal neuronal densities, as well hippocampal neurogenesis in С57BL/6J mice. Offspring of naturally born C57BL/6J mice (C57BL group) were compared with C57BL/6J mice born as a result of the IVC combined with ET to C57BL/6J recipient females (ET-C57BL group). At age of 3 mo., no group differences were observed in the body weight and brain-to-body ratio, although sex differences in these variables were observed. The offspring of both sexes born after IVC-ET exhibited the lower level of neurogenesis in the dentate gyrus (DG) of the hippocampus as compared to the control C57BL group. To conclude, IVC and ET exerted no major effects on body and brain weight in offspring, but affected hippocampal neurogenesis in the adult offspring of both sexes. Besides, the number of pyramidal neurons in the CA3 area of hippocampus was lower in female offspring of ET-C57BL group.

Seasonal Presence of White Fly Species on Jujube Trees in Nineveh Governorate

The study was conducted in the gardens of Mosul University from September 2019 to September 2020 in order to determine the types of white flies that infest Jujube trees and their seasonal activity. The results showed that Jujube trees, Zizyphus spina Christi, were infected with the following species: Acaudaleyrodes rachipora (Singh), Aleurolobus marlatti (Quan), and Aleuroclava jasmini (Takahashi). The percentage of leaf infection was highest in November, followed by September and August with an average 98.95, 94.85 and 94.63%, respectively. The insect preferred upper surface of the leaf than its lower surface, as the average number of nymphs was 15,11, and 1,39 nymphs/leaf, respectively, and the number of nymphs peaked during the autumn months. Direction had no effect on the rate of leaves infection, and no significant differences appeared between the treatments, while the density of nymphs in the leaves was affected by the direction factor, as the southern direction was significantly superior at a rate of 18.85 nymphs/leaf, and no significant differences were recorded between the other three directions. The results of the weekly catch also showed that the density of adults ranged between (1.28-168) adult /trap, peaking in October, while the adult were absent from the traps during January and February. Some predators were seen preying on the stages of the white fly, Lasiochilus pallidulus (Reuter), Oenepia conglobate (L.), Chrysoperla carnea (Stepheus).

The Density of Aedes albopictus in a High-Latitude and High-Risk Dengue Fever Transmission Region in Shandong Province, Northern China.

Background: A total of 79 cases of dengue fever were reported in Jining County in 2017, which is currently the northernmost focal point of local cases of dengue fever diagnosed in China. This study aimed to evaluate the density of mosquito vectors before and after the outbreak of dengue fever and provide novel reference data for the prevention and control of the disease. Methods: The light traps were set to collect mosquitoes in 2017 and 2018 to assess adult mosquito density and species composition. We used the human-baited double net trap to determine the biting rate. In addition, the Breteau index (BI) was calculated to evaluate the density of Aedes albopictus in Jining, Shandong Province. The annual average densities of Ae. albopictus in 2017 and 2018 were 0.046 and 0.066 f/t/h, respectively. Results: The average biting rate was 0.69 f/m/h in 2018. There was no significant difference found in Ae. albopictus density and biting rate in the various months. The average BI of Jining was 38.67 and 11.17, respectively. There was a statistically significant difference observed in the BI between 2017 and 2018 (Kruskal-Wallis test, χ2 = 16.926, df = 1, p < 0.001). Conclusion: BI can serve as an important indicator to determine the spread of dengue fever. The findings indicted that the growing density of adult Aedes mosquitoes should be focused on, with biting rates being a potential indicator of future outbreaks. Overall, the various control measures that were implemented were effective and should be introduced in other high-risk areas.

Adult conspecific density affects Janzen-Connell patterns by modulating the recruitment exclusion zones.

Our model highlights the complex interconnection between NF intensity, stand density, and recruitment patterns explaining where and why the JC distribution occurs. Moreover, predicting the occurrence of JC in relation to stand density we clarify the relevance of this ecological phenomenon for future integration in plant community frameworks.

High-latitude invasion and environmental adaptability of the freshwater mussel Limnoperna fortunei in Beijing, China.

The invasive freshwater mussel Limnoperna fortunei (Dunker, 1857) has spread widely throughout Asia and South America, especially via interbasin water diversion and navigation. The middle route of the South-to-North Water Transfer Project (SNWTP), whose terminal is Beijing, has diverted more than 60 billion m3 of water from the Yangtze River Basin to Northern China since December 2014. L. fortunei has spread north to Beijing along the SNWTP, biofouling its channels and tunnels. To determine the status of L. fortunei's invasion in Beijing, we systematically inspected the water bodies receiving southern water, including all branches of the SNWTP, water treatment plants, lakes, reservoirs, and rivers. We measured the densities of adults and veligers of L. fortunei and conducted eDNA analyses of water samples. A generalized linear model and canonical correspondence analysis were adopted to investigate the correlations between environmental (e.g., water temperature, conductivity, pH, total nitrogen, and phosphorus) and biological (e.g., chlorophyll a, plankton density, and community composition) variables and the densities of adults and veligers of L. fortunei. Water temperature is the most important factor in determining the densities of D-shaped and pediveliger veligers, with explanatory variable contributions of 56.2% and 43.9%, respectively. The pH affects the densities of D-shaped, umbonated, and pediveliger veligers. The density of plantigrade veligers is negatively correlated with the conductivity and positively correlated with the concentration of chlorophyll a. Canonical correspondence analysis shows a weak correlation between the dominant phytoplankton taxa and the density of veligers. The densities of D-shaped, umbonated, and pediveliger veligers are positively correlated with the density of small phytoplankton (12.54 ± 4.33 μm), and the density of plantigrade veligers is positively correlated with the density of large (16.12 ± 5.96 μm) phytoplankton. The density of planktonic veligers is well correlated with local abiotic variables, and that of plantigrade veligers is less correlated with local abiotic variables. This finding implies that controlling early-stage veligers by altering water temperature, pH, and food size might effectively control the establishment of further L. fortunei colonies.

Pear psylla and natural enemy thresholds for successful integrated pest management in pears.

Pear psylla, Cacopsylla pyricola (Förster), is the most economically challenging pest of commercial pears in Washington and Oregon, the top producers of pears in the United States. The objective of this study was to quantify economic injury levels and thresholds for pear psylla. We used the relationship between pear psylla adult and nymph densities, and fruit downgraded due to psylla honeydew marking to identify injury levels. We calculated economic injury levels using the cost of downgraded fruit and average management costs (spray materials and labor). Using economic injury levels, we determined economic thresholds for pear psylla, which include predicted pest population growth, natural enemy predation, and anticipated delays between when pest populations are measured and when managers apply interventions. Economic thresholds generated by this study were 0.1-0.3 second-generation nymphs per leaf and 0.2-0.8 third-generation nymphs per leaf depending on predicted price and yield for insecticide applications at 1,300 pear psylla degree days in the second generation and 2,600 pear psylla degree days in the third generation. Natural enemy inaction thresholds identified by this study were 6 Deraeocoris brevis or 3 Campylomma verbasci immatures per 30 trays or 2 earwigs per trap for third-generation optional insecticide applications.

Toward optimising reproductive output of Eristalis tenax (Diptera: Syrphidae) for commercial mass rearing systems

AbstractDeveloping mass rearing systems for the drone fly, Eristalis tenax, is a crucial step toward its use as a complementary commercial pollinator. To meet the timing of commercial needs for E. tenax, there is significant value to both predicting and managing reproductive output and development within the rearing protocol. To help achieve this, our study focuses on the laboratory manipulation of adult mating and the timing of the development of eggs in E. tenax. To stagger colony cohorts, egg rearing temperatures ranging from 12 to 30°C were found to be suitable for both successful egg development and hatching viability (97 to 28.3 h to first hatch, respectively). The mating window for E. tenax females was established to commence from 2 weeks post eclosion and reached 75 ± 11% mated at 7 weeks. Reproductive output over 12 weeks was assessed in separate cage manipulation trials: (1) varying the sex ratio with 20:40, 30:30 and 40:20 female and male flies respectively per cage and (2) varying the adult density per cage with 15:15, 30:30, 60:60 and 120:120 female and male flies per cage. Female percentage mated and egg cluster size, which averaged 200.6 ± 4.3 eggs per cluster, did not change between treatments in the sex ratio and density trials. Egg cluster output per female was significantly reduced for treatments across both trials, which had more than 30 females in a cage. A stocking rate of 15:15 produced 86% more eggs per female than expected, a percentage well above that of all other treatments. However, the highest stocking density produced the most eggs when assessed at a per cage level. Fly survival was significantly different between the sexes across both trials with males dying earlier in cages stocked with more females than males. Although the fly colonies were held at constant temperatures and light conditions for 6 months, we found evidence of endogenous overwintering behaviours among flies resulting in lower mating rates, egg hatching success and greater longevity among flies studied over winter.

Time series analysis showing how different environmental conditions affect the interspecific interactions of Callosobruchus maculatus and Callosobruchus chinensis

AbstractEnvironmental changes alter the strength of interspecific interactions. However, because it is difficult to quantify interaction strength, empirical evidence remains limited on the relationships among environmental change, interaction strength, and consequences on population dynamics. Here, we evaluated how the interactions of two species of Callosobruchus seed beetles changed with increasing the cage size of the experiments and then affected the coexistence period as a property of population dynamics. Specifically, competition experiments were conducted on Callosobruchus maculatus (C. maculatus) and Callosobruchus chinensis (C. chinensis) using cages of different sizes, which altered the density of adults. We focused on two modes of interspecific interactions between these two species: larval resource competition and adult reproductive interference. Convergent cross mapping (CCM) was implemented to the experimental time series of the two species to assess how environmental change altered their interaction strength and the coexistence period (as a proxy of population dynamics). In most replications, C. maculatus persisted, whereas C. chinensis became extinct. The coexistence periods were longer with increasing cage size. However, there was no statistically significant relationship between cage size and interaction strength. Nevertheless, the stronger (or weaker) interaction strength of the competitively inferior (superior) species on competitively superior (inferior) was associated with longer coexistence periods. Overall, this study demonstrated that interaction strength affected population dynamics; however, changing interaction strength by altering environmental conditions did not necessarily mean that increasing habitat size reduces competition strength.