Egg Mass Density Research Articles

Effects of natural flooding and manual trapping on the facilitation of invasive crayfish-native amphibian coexistence in a semi-arid perennial stream

Aquatic amphibians are known to be vulnerable to a myriad of invasive predators. Invasive crayfish are thought to have eliminated native populations of amphibians in some streams in the semi-arid Santa Monica Mountains of southern California. Despite their toxic skin secretions that defend them from native predators, newts are vulnerable to crayfish attacks, and crayfish have been observed attacking adult newts, and eating newt egg masses and larvae. For 15 years, we have observed invasive crayfish and native California newts coexisting in one stream in the Santa Monica Mountains. During that period, we monitored the densities of both crayfish and newt egg mass densities and compared these to annual rainfall totals. After three seasons of below average rainfall, we reduced crayfish numbers by manual trapping. Our long-term data indicated that crayfish did not fare well in years when rainfall is above the historic average. This invasive predator did not evolve with high velocity streams, and observations indicated that southern California storm events washed crayfish downstream, killing many of them. Newts exhibit increased reproduction in years when crayfish numbers were reduced. A comparison with a nearby stream that does not contain crayfish indicated that newt reproduction positively responded to increased rainfall, but that fluctuations were much greater in the stream that contains crayfish. We suggest that rainfall patterns help explain invasive crayfish/newt coexistence and that management for future coexistence may benefit from manual trapping.

The influence of planting date, transgenic Bt maize and hybrid relative maturity on European corn borer Ostrinia nubilalis (Lepidoptera: Crambidae) ovipositional patterns

AbstractA three year study was carried out at Hoytville and at Wooster, Ohio, USA from 2006 to 2008 to investigate the influence of planting date, transgenic maize and hybrid maturity on Ostrinia nubilalis (Hubner) population dynamics and oviposition patterns. Maize plants were planted in late April or early May, mid‐May and early June during each year. The moth flight pattern showed bivoltine generations during the three years. The first moth flight peaked in June, with the populations declining during July. The second moth flight peaked in August and declined towards the end of September or early October. Egg mass density did not differ significantly between transgenic and non‐transgenic maize of different maturities. Significant differences were observed, however, among planting dates, sampling dates, and sampling date × planting date interactions. Generally higher numbers of egg masses from second generation moths were deposited on late planted maize than middle and early plantings.

Environmental constraints on oviposition of aquatic invertebrates with contrasting life cycles in two human‐modified streams

Summary Many streams today have modified channels, substratum composition, flows and temperature regimes. Understanding how these potential stressors affect key processes governing populations is crucial towards counteracting species decline and loss. For aquatic organisms with complex life cycles that include a terrestrial adult stage, successful reproduction involving a transition from the terrestrial to aquatic environment for oviposition can be an important constraint. Our main goal was to test for the effects of local stream degradation on egg mass densities of macroinvertebrates with different requirements for oviposition habitat. We experimentally manipulated oviposition substrate availability in two Swiss gravel‐bed rivers by adding bricks to stream beds of channelised, restored and near natural reaches differing in their depth profile and availability of large rocks. We followed oviposition on bricks and natural rocks between May and October 2008 and quantified egg mass densities of two aquatic insects with a terrestrial stage (Baetis spp. and Hydropsyche spp.) and an entirely aquatic leech Erpobdella octoculata. Individual and interactive effects of mean water depth fluctuations, depth variability, frequency of large rocks and temperature on egg mass densities were evaluated using a model selection approach. Response to our manipulation in terms of relative use of bricks for oviposition was strongest in the two insect taxa, whose egg mass densities responded to the presence of large substrata in study reaches. We also found evidence for a weak water level effect on egg mass densities of Baetis, a mayfly that uses protruding rocks for oviposition, in contrast to Hydropsyche, which apparently is capable of diving. While no clear response to our manipulation was found in Erpobdella octoculata, its overall cocoon densities were influenced by the variability of depth profile and increased in reaches with lower streambed heterogeneity. Our results suggest that stream degradation has high potential to constrain reproduction of many species, in particular those with complex life cycles such as aquatic insects. Investigation in modified riverscapes of the specific effects of different constraints to recruitment processes is a prerequisite for successful management and conservation.

Evaluation of Potential Versus Realized Primary Infection of Gypsy Moth (Lepidoptera: Lymantriidae) byEntomophaga maimaiga(Zygomycetes: Entomophthorales)

The fungal entomopathogen Entomophaga maimaiga has provided important biological control of gypsy moth, Lymantria dispar (L.), since the first epizootics occurred in the northeastern United States in 1989. Epizootics are initiated by germination of soil-borne resting spores, which are highly sensitive to spring temperature and moisture. We compared gypsy moth infection by E. maimaiga in 33 oak stands in Michigan with infection under optimal laboratory conditions from 1999 to 2001 to assess differences between potential and realized efficacy of E. maimaiga. Field bioassays were conducted by exposing laboratory-reared, fourth-instar gypsy moth to soil at the base of oak trees for 4 d. Additional larvae were similarly exposed to soil collected from the field plots in laboratory bioassays with temperature, humidity, and moisture levels optimal for fungal germination. Overall E. maimaiga infection ranged from means of 3.2-29.8% in the field compared with 20.9-59.7% in the laboratory during three field seasons. Resting spore density in soil and gypsy moth egg mass density were significant predictors of field infections in two of the 3 yr, whereas resting spore density was a significant predictor of laboratory infections each year. Other variables that significantly predicted laboratory infections in one of the 3 yr included egg mass density, canopy cover, and soil pH. In laboratory bioassays, soil pH and E. maimaiga resting spore density were positively associated with increasing E. maimaiga infection rates of gypsy moth larvae.

C. P. Alexander review

AbstractThe Canadian registration in 2007 of Disrupt SBW Micro-Flakes®, a pheromone-based product for control of spruce budworm,Choristoneura fumiferana(Clemens), paved the way for large-scale trials to test the practicality of mating disruption as a commercial pest management strategy. We review results from field and laboratory experiments on pheromone-based mating disruption of spruce budworm conducted from 1974 to 2008. Application of pheromone from the ground or the air consistently reduced the orientation of males toward pheromone sources. Mating disruption also reduced the mating success of caged or tethered females in 15 of 16 field studies where this parameter was recorded, but had only a limited effect on the mating success of feral females. No consistent difference in the density of egg masses in control and treated plots was observed, which has often been attributed to immigration of gravid females into pheromone-treated plots. Laboratory studies suggest that false-trail following is the predominant mechanism underlying mating disruption in spruce budworm. The enhanced mating success of females with increasing population density suggests that mating disruption should target low-density emergent populations during the initial phase of an outbreak. Constraints that may limit the potential of mating disruption as a management tool include (1) difficulties associated with obtaining accurate sampling estimates at low population density to forecast the onset of outbreaks, (2) potential behavioral adaptations by which females enhance their mating success when the atmosphere is treated with pheromone, and (3) long-range dispersal of females by flight.

转Cry1Ab和Cry1Ac融合基因型抗虫水稻对田间二化螟和大螟种群发生动态的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 转Cry1Ab和Cry1Ac融合基因型抗虫水稻对田间二化螟和大螟种群发生动态的影响 DOI: 10.5846/stxb201102260222 作者: 作者单位: 南京农业大学植物保护学院昆虫学系,南京农业大学植物保护学院昆虫学系,南京农业大学植物保护学院昆虫学系,南京农业科学研究院植物保护研究所水稻害虫研究组,南京农业大学植物保护学院昆虫学系 作者简介: 通讯作者: 中图分类号: 基金项目: 转基因生物新品种培育重大专项课题(2009ZX08011-007B; 2009ZX08012-005B和2011ZX08012-005); 教育部霍英东基金(122033); 博士点基金(20070307002) Effects of insect-resistant transgenic Bt rice with a fused Cry1Ab+Cry1Ac gene on population dynamics of the stem borers, Chilo suppressalis and Sesamia inferens, occurring in paddyfield Author: Affiliation: Department of Entomology, College of Plant Protections, Nanjing Agricultural University,Department of Entomology, College of Plant Protections, Nanjing Agricultural University,Department of Entomology, College of Plant Protections, Nanjing Agricultural University,Institute of Plant Protection, Chinese Academy of Agricultural Sciences,Department of Entomology, College of Plant Protections, Nanjing Agricultural University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以Bt水稻华恢1号(Cry1Ac和CryAb融合基因;简称HH1)及其对照亲本明恢63(简称MH63)稻田靶标害虫二化螟Chilo suppressalis和次靶标害虫大螟Sesamia inferens为研究对象,研究了转基因抗虫水稻大田螟虫发生规律及其靶标和次靶标害虫致害力差异。结果表明,Bt水稻及其对照亲本上二化螟或大螟的卵块数量差异不显著,同时,对照亲本上二化螟与大螟的落卵量差异不显著,但Bt水稻上二化螟的落卵量显著大于大螟。与对照亲本相比,Bt水稻上二化螟幼虫发生量显著降低,降幅高达84.9%-100%,但大螟发生量差异不显著;此外,对照亲本上二化螟幼虫发生量显著高于大螟,但Bt水稻上两者差异不显著。同时,Bt水稻上二化螟导致的枯心/白穗率和受害丛率都显著低于其在对照亲本上的致害程度,降幅分别为30.8%-98.3%和11.4%-96.6%,而大螟差异不显著。可见,Bt水稻对靶标害虫二化螟具有较高抗性,而对次靶标害虫大螟的抗性不明显。另一方面,Bt水稻和对照亲本上二化螟导致的枯心/白穗率和受害从率都显著高于大螟。可见,二化螟仍是当前非转基因水稻上的主要害虫,而Bt水稻对二化螟幼虫发生的显著抑制作用以及对大螟幼虫发生的不显著影响,使得其大面积商业化种植下靶标害虫二化螟和次靶标害虫大螟间的竞争替代成为可能。 Abstract:The approval of transgenic Bacillus thuringiensis rice (ab., Bt rice) with double-stacked traits (including a rice restorer line of cv. Bt Huahui-1 and a hybrid rice line of cv. Bt Shanyou-63, both expressing a fused Cry1Ab+Cry1Ac gene) by China's Ministry of Agriculture (MOA) on 27 November 2009 was a momentous day for biotech crops worldwide. To date, some experiments have been carried out in labs or under controlled environmental conditions, which indicate that Bt rice can perform remarkably well against two targeted lepidopteran pests (e.g., the stem borer, Chilo suppressalis, and leaf-folder, Cnaphalocrocis medinalis), and simultaneously offers: 1) the potential to generate economic benefits due to yield increases, and 2) overall decreases in insecticide use in China. In this study, the field experiments were conducted in order to examine the population dynamics and damage characteristics of two stem borers (i.e., target pest, C. suppressalis and a sub-target pest, Sesamia inferens) feeding on the Bt rice with a fused Cry1Ab+Cry1Ac gene (cv., Bt Huahui-1) and its parent line of nontransgenic rice (cv., Minghui-63). The results indicate that no significant differences were found in the number of egg masses per 100 plants for C. suppressalis or S. inferens occurring on Bt rice in contrast to nontransgenic rice. In addition, no significant differences in egg mass densities between C. suppressalis and S. inferens were found when fed on nontransgenic rice, whereasas a significant increase in egg mass were observed for C. suppressalis relative to S. inferens fed on Bt rice. Compared with nontransgenic rice, Bt rice significantly reduced the population density (i.e., individuals per 100 plants; 84.9%-100%) of C. suppressalis larvae, while the transgenicity did not significantly influence the population abundance for S. inferens. Moreover, C. suppressalis had significantly higher larval abundances than S. inferens when they fed on nontransgenic rice, while no significant differences were observed when fed on Bt rice. Simultaneously, significantly lower percentages of dead heart or white head plants (30.8%-98.3%), and damaged plants (11.4%-96.6%) resulted from C. suppressalis, while no significant differences were detected in the damage percentages for S. inferens, as they fed on the Bt rice relative to the nontransgenic rice cultivar. Therefore, Bt rice appears to have a higher resistance to the targeted pest, C. suppressalis, while lower resistance was observed for the sub-target pest,S. inferens. Furthermore, significantly higher damage percentages were caused by C. suppressalis relative to S. inferens, regardless of the transgenicity of the rice cultivar. Thus, the stem borer, C. suppressalis, remains the key insect pest in the paddyfield. While it is presumed, owing to the significant inhibition of Bt rice on the occurrence of C. suppressalis relative to S. inferens under the commercialization usage of Bt rice, the inter-species competition and population succession may be occurring between the target and sub-target pests of stem borers. Furthermore, additional field research work needs to be conducted, especially during the rice growing season when high densities of C. suppressalis and S. inferens are both available on Bt rice to assess ecological risks of the inter-species competition and population successions between the target and sub-target insect pests. 参考文献 相似文献 引证文献

Lasting effects of maternal behaviour on the distribution of a dispersive stream insect

1. Predicting population dynamics at large spatial scales requires integrating information about spatial distribution patterns, inter-patch movement rates and within-patch processes. Advective dispersal of aquatic species by water movement is considered paramount to understanding their population dynamics. Rivers are model advective systems, and the larvae of baetid mayflies are considered quintessential dispersers. Egg laying of baetids along channels is patchy and reflects the distribution of oviposition sites, but larvae are assumed to drift frequently and far, thereby erasing patterns created during oviposition. Dispersal kernels are often overestimated, however, and empirical tests of such assumptions are warranted because of the pivotal role distribution patterns can have on populations. 2. We tested empirically whether the egg distribution patterns arising from oviposition behaviours persisted and were reflected in the distribution patterns of larval Baetis rhodani. In field surveys, we tested for associations between egg mass and larval densities over 1 km lengths of four streams. A control species, the mayfly Ephemerella ignita, was employed to test for covarying environmental factors. We estimated drift rates directly to test whether larvae dispersed between riffles (patches of high egg mass density) and whether drift rates were density-dependent or density-related - expected outcomes if drift erases patterns established by maternal behaviours. 3. Positive associations between egg masses and larval benthic densities were found for neonate and mid-stage larvae of Baetis, but not the control species, suggesting persistence of the patchy distribution patterns established at oviposition. Drift rates were high, and riffles were net exporters of neonate and mid-stage larvae, but drift rates were unrelated to benthic densities and few drifters reached the next riffle. Riffles were sinks for large larvae, suggesting ontogenetic shifts in habitat use, but little long-distance dispersal. 4. Overall, the results suggest that most neonate and mid-stage larvae of B. rhodani remain close to the natal riffle, and late-stage larvae disperse shorter distances than routinely assumed. The persistence of maternal effects on distribution patterns well into juvenile life of an allegedly iconic disperser suggests that traditional models of how dispersal influences the population dynamics of many lotic invertebrates may be incorrect.

Ventilation plays an important role in hens' egg production at high ambient temperature

Birds dissipate considerable heat through respiratory-evaporative and cutaneous-evaporative mechanisms and sensible heat loss (SHL) via radiation, convection, and conduction. The significance of SHL in laying hens is still to be confirmed. This study aimed to elucidate the effect of ventilation on egg production and quality during exposure to high ambient temperature. Lohman laying hens were raised outdoors up to age 35 wk, and 300 hens with similar egg production were divided among 5 treatments each comprising 4 replicates of 15 hens. Birds in 4 treatments were kept in computerized controlled-environment rooms acclimated to 35°C and 50% RH, with ventilation flow rates of 0.5, 1.5, 2.0, and 3.0 m/s, respectively, and those in the control were kept outdoors. Hens were acclimated to the controlled environment rooms for 1 wk and to the targeted environmental conditions for another week, and then were subjected to measurements for 2 wk. Egg production, mass, and shell density, and feed and water consumption were monitored. Body temperature, SHL, and plasma thyroid hormone concentrations were measured at the end of the experiment. The high environmental temperature impaired egg production and quality: whereas exposure of hens to ventilation flows of 2.0 and 3.0 m/s elicited significant recovery of these parameters with time, exposure to a rate of 0.5 m/s negatively affected these parameters throughout the experimental period. The highest feed intake and water consumption were observed in hens exposed to 2.0 and 3.0 m/s, respectively, and the highest SHL was observed in those exposed to 3.0 m/s. It can be concluded that ventilation rate significantly affected hens exposed to high ambient temperature: high ventilation (3.0 m/s) improved egg production whereas low ventilation (0.5 m/s) negatively affected production and quality.

Oviposition Behavior and Larval Development of the European Corn Borer (Lepidoptera: Crambidae) on Sweet Versus Hot Peppers

Infestation of European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), a key pest of peppers (Capsicum annuum L.), was studied to explore the cause of infestation differences in pungent versus sweet types of peppers. Our objectives were to determine whether O. nubilalis adults show an ovipositional preference or larval development effects among pepper types that vary in levels of capsaicin and dihydrocapsaicin, which is measured in Scoville heat units (SHU). Five pepper types with a range in hotness were tested: bell (0 SHU), sweet banana (0 SHU), hot wax (1125 SHU), jalapeño (5,000 SHU), and cayenne (40,000 SHU). Oviposition was studied after artificial infestation in laboratory cages, small and large field cages, and after natural infestation in choice and no-choice field trials. No ovipositional preference was detected for cage no-choice or choice assays. Field choice oviposition trials with 5 pepper types had no differences in either egg mass density or larval infestation. A no-choice field trial with 3 pepper types found there was no difference in oviposition, but larval infestation varied significantly, with bell peppers having the highest infestation and jalapeños the least. It is concluded that O. nubilalis females show no ovipositional preference among the pepper types tested. Larval development time was significantly longer on jalapeños and significantly longer on pungent than on sweet peppers. Larval survival was not significantly different among types. These results suggest that the difference in infestation must be due to behavioral or physical factors after egg laying and before larvae enter the fruit.

Stimuli associated with viburnum leaf beetle (Pyrrhalta viburni) aggregative oviposition behavior

Viburnum leaf beetle, Pyrrhalta viburni (Paykull) (Coleoptera: Chrysomelidae), oviposits in terminal twigs of Viburnum spp. shrubs (Caprifoliaceae). Twigs react to oviposition by producing neoplasm that overgrows the egg mass. Pyrrhalta viburni oviposition behavior is aggregative: females prefer to lay egg masses on twigs previously infested by other females and to position their egg masses adjacent to existing ones. Female oviposition preferences were studied in a series of choice tests under laboratory conditions. The three components of the egg mass (cavity, eggs, and egg cap) were not sufficient to elicit complete aggregation oviposition response when presented separately. Cavity and egg cap elicited positional preference, but not the artificial cavity, artificial egg cap, or frass, suggesting that stimulatory cues might be associated with insect saliva and egg cap secretion. Females preferred to lay eggs on twigs that had produced wound tissue in response to previous oviposition. We conclude that twig choice and positional preference for oviposition are likely to be dissociated, and that twig wound response might be used by P. viburni females to locate twigs already infested and possibly less defended against subsequent oviposition. Pyrrhalta viburni females preferred to lay egg masses on heavily infested twigs rather than on lightly infested twigs. Females did not show preference for twigs infested with their own egg masses, but laid more egg masses on twigs infested by multiple females than on twigs infested by single females. We conclude that both egg mass and conspecific density affect oviposition preferences of P. viburni and discuss the possible ecological implications of this behavior.

Environmental constraints on oviposition limit egg supply of a stream insect at multiple scales

Species with complex life cycles pose challenges for understanding what processes regulate population densities, especially if some life stages disperse. Most studies of such animals that are thought to be recruitment limited focus on the idea that juvenile mortality limits the density of recruits (and hence population density), fewer consider the possibility that egg supply may be important. For species that oviposit on specific substrata, environmental constraints on oviposition sites may limit egg supply. Female mayflies in the genus Baetis lay egg masses on the underside of stream rocks that emerge above the water's surface. We tested the hypothesis that egg mass densities are constrained by emergent rock densities within and between streams, by counting egg masses on emergent rocks. All emergent rocks were counted along 1-km lengths of four streams, revealing significant variation in emergent rock density within streams and a more than three-fold difference between streams. In each stream, egg mass density increased with the density of emergent rocks in 30-m stretches. We used regression equations describing these small-scale relationships, coupled with the large-scale spatial variation of emergent rocks, to estimate egg mass densities for each 1-km stream length, a scale relevant to population processes. Scaled estimates were positively associated with emergent rock density and provided better estimates than methods that ignored environmental variation. Egg mass crowding was inversely related to emergent rock density at the stream scale, a pattern consistent with the idea that oviposition substrata were in short supply in streams with few emergent rocks, but crowding did not compensate entirely for differences in emergent rock densities. The notion that egg supply, not larval mortality, may limit population density is an unusual perspective for stream insects. Environmental constraints on egg supply may be widespread among other species with specialised oviposition behaviours.

Amphibian production in forested landscapes in relation to wetland hydroperiod: A case study of vernal pools and beaver ponds

Many amphibian species are plastic in their selection of breeding sites and use both short- and longer-hydroperiod wetlands. Understanding which wetland types are most important to amphibian production is critical for focusing conservation efforts. We compared reproduction of wood frogs ( Rana sylvatica) and spotted salamanders ( Ambystoma maculatum) and production of wood frog juveniles between seasonal (vernal pools) and semi-permanent (beaver-created ponds) wetlands in the central Adirondack region of the northeastern United States. In 65 seasonal wetlands and 37 semi-permanent wetlands over 3 years, densities of wood frog egg masses were similar, but seasonal wetlands contained 4× as many spotted salamander egg masses as did semi-permanent wetlands. For wood frogs, survival to metamorphosis and juvenile production were an order of magnitude higher in semi-permanent wetlands. Models of wood frog production linked to the climatic record predicted that, depending on annual variation in rainfall and survival to metamorphosis, semi-permanent wetlands may produce annually 1.2–23× the number of wood frogs that seasonal wetlands produce within the study area. Models incorporating variation in demographic traits throughout the range of wood frogs suggest that higher survival to metamorphosis in beaver ponds and higher clutch densities in vernal pools strongly influence metamorph production on a regional basis. Semi-permanent wetlands make major contributions to amphibian production in our region and may also be an important source of colonists to seasonal wetlands following periods of drought. Protection of wetlands along the landscape-level continuum of hydroperiod therefore may be critical for maintaining and restoring amphibian populations.

Influence of intra‐tree variation in phenology and oviposition site on the distribution and performance of Ennomos subsignaria on mature sycamore maple

Abstract 1. Field surveys and a manipulative experiment were conducted to examine the hypotheses that intra‐tree heterogeneity in natural enemy activity, foliar quality (independent of phenology), or phenology influence the intra‐tree distribution and performance of Ennomos subsignaria on mature sycamore maple, Acer pseudoplatanus.2. Ennomos subsignaria intra‐tree distribution was distinctly clumped. Egg mass density was 85% higher on the lower bole than in the crown. Most early instars were found on lower crown proximal branches while most late instars and pupae were found on lower crown distal branches. This resulted in high levels of defoliation in the lower crown, especially on proximal branches.3. No parasitoids were reared from eggs or late‐instar larvae and only one pupa was parasitised, suggesting that preference for the bole and lower crown was not a response to parasitism. Similarly, E. subsignaria performance was not influenced by variable foliage quality (independent of phenology) within the crown. However, sycamore maple phenology had a large influence on E. subsignaria survival. More than 90% of newly emerged larvae survived to the adult stage when they fed on foliage with three pairs of leaves expanded per bud, whereas survival on younger foliage was reduced by >45%.4. The peak period of E. subsignaria egg hatch was approximately 2 weeks after the peak period of sycamore maple budburst, which occurred acropetally. Egg hatch was closely synchronised with the availability of most suitable leaves for insect development on proximal branches of the lower crown, the location where most larvae initiated feeding.5. The results support the phenology hypothesis and suggest that intra‐tree variation in oviposition site and host phenological development influence the intra‐tree distribution and performance of this generalist herbivore.

Open field host selection and behavior by tamarisk beetles ( Diorhabda spp.) (Coleoptera: Chrysomelidae) in biological control of exotic saltcedars ( Tamarix spp.) and risks to non-target athel ( T. aphylla) and native Frankenia spp.

Biological control of invasive saltcedars ( Tamarix spp.) in the western U.S. by exotic tamarisk leaf beetles, Diorhabda spp., first released in 2001 after 15 years of development, has been successful. In Texas, beetles from Crete, Greece were first released in 2004 and are providing control. However, adults alight, feed and oviposit on athel ( Tamarix aphylla), an evergreen tree used for shade and as a windbreak in the southwestern U.S. and México, and occasionally feed on native Frankenia spp. plants. The ability of tamarisk beetles to establish on these potential field hosts was investigated in the field. In no-choice tests in bagged branches, beetle species from Crete and Sfax, Tunisia produced 30–45% as many egg masses and 40–60% as many larvae on athel as on saltcedar. In uncaged choice tests in south Texas, adult, egg mass and larval densities were 10-fold higher on saltcedar than on adjacent athel trees after 2 weeks, and damage by the beetles was 2- to 10-fold greater on saltcedar. At a site near Big Spring, in west-central Texas, adults, egg masses and 1st and 2nd instar larvae were 2- to 8-fold more abundant on saltcedar than on athel planted within a mature saltcedar stand being defoliated by Crete beetles, and beetles were 200-fold or less abundant or not found at all on Frankenia. At a site near Lovelock, Nevada, damage by beetles of a species collected from Fukang, China was 12–78% higher on saltcedar than on athel planted among mature saltcedar trees undergoing defoliation. The results demonstrate that 50–90% reduced oviposition on athel and beetle dispersal patterns within resident saltcedar limit the ability of Diorhabda spp. to establish populations and have impact on athel in the field.

Preoutbreak Dynamics of a Recently Established Invasive Herbivore: Roles of Natural Enemies and Habitat Structure in Stage-Specific Performance of Gypsy Moth (Lepidoptera: Lymantriidae) Populations in Northeastern Wisconsin

A major challenge to addressing biological invasions is that the need for emergency responses often precludes opportunities to analyze the dynamics between initial establishment and population eruption. Thus, a broader understanding of underlying processes and management opportunities is often lacking. We examined the effects of habitat structure and natural enemies on recently established preeruptive gypsy moth, Lymantria dispar L., populations over 4 yr in northeastern Wisconsin. Forty-five sites were established across a range of habitat structures in oak-dominated northern hardwood forests. The number of egg masses was positively related to percent composition of oaks and other favored species. Other life stages were not related to habitat structure variables. Abundance of each life stage can predict the subsequent life stage with variable degrees of accuracy, but male moth densities were only a weak predictor of egg mass or larval densities the following year. The parasitic fly Compsilura concinnata (Meigen), an introduced generalist with deleterious nontarget effects, caused the highest mortality to larvae. The specialist pathogens Entomophaga maimaiga and nucleopolyhedrosis virus were widely distributed but caused less mortality than reported in the northeastern United States, where gypsy moth has been established much longer. Small mammals are the major predators of pupae as elsewhere, but invertebrates seem less important along the western than southern advancing front of gypsy moth. Overall habitat structure did not influence natural enemy populations. These results suggest that the pre-eruptive phase is distinct from the pre-establishment phase by high mating success and from the eruptive phase by the prominent role of generalist natural enemies. Improved understanding of these dynamics can help guide silvicultural and biocontrol strategies in newly invaded regions of the Midwest and provide general insight into invasive forest defoliators.

Suppression of <I>Ennomos subsignaria</I> (Lepidoptera: Geometridae) on <I>Acer pseudoplatanus</I> (Aceraceae) in an Urban Forest with Bole-Implanted Acephate

Trees in an urban forest are highly valued because they have esthetic appeal, provide shade, and improve air quality. During the past 5 yr (2002-2006) in St. John's, Newfoundland and Labrador, Canada, the elm spanworm, Ennomos subsignaria (Hübner) (Lepidoptera: Geometridae), has reached outbreak densities. Each year, hundreds of trees have been completely defoliated, and many more trees have been partially defoliated. Adding to this problem, the larvae, their silk strands, and their frass are a considerable nuisance to property owners in areas of high larval densities. In this study, we evaluated the efficacy of three doses of bole-implanted acephate (AceCap 97) for reducing densities and associated defoliation of E. subsignaria on sycamore maple, Acer pseudoplatanus L. (Aceraceae). During the treatment year (2005), all three doses significantly reduced E. subsignaria larval and pupal density; full or two-thirds doses significantly reduced defoliation compared with control trees. During the posttreatment year (2006), bole-implanted acephate did not affect E. subsignaria egg mass density, survival (= adult emergence), or defoliation. Bole-implanted acephate is an effective and practical way of suppressing E. subsignaria densities and herbivory in an urban forest where the protection of high-value trees and the reduction of environmental contamination are of utmost importance.

Suppression of Ennomos subsignaria (Lepidoptera: Geometridae) on Acer pseudoplatanus (Aceraceae) in an Urban Forest with Bole-Implanted Acephate

Trees in an urban forest are highly valued because they have esthetic appeal, provide shade, and improve air quality. During the past 5 yr (2002–2006) in St. John’s, Newfoundland and Labrador, Canada, the elm spanworm, Ennomos subsignaria (Hübner) (Lepidoptera: Geometridae), has reached outbreak densities. Each year, hundreds of trees have been completely defoliated, and many more trees have been partially defoliated. Adding to this problem, the larvae, their silk strands, and their frass are a considerable nuisance to property owners in areas of high larval densities. In this study, we evaluated the efficacy of three doses of bole-implanted acephate (AceCap 97) for reducing densities and associated defoliation of E. subsignaria on sycamore maple, Acer pseudoplatanus L. (Aceraceae). During the treatment year (2005), all three doses significantly reduced E. subsignaria larval and pupal density; full or two-thirds doses significantly reduced defoliation compared with control trees. During the posttreatment year (2006), bole-implanted acephate did not affect E. subsignaria egg mass density, survival (=adult emergence), or defoliation. Bole-implanted acephate is an effective and practical way of suppressing E. subsignaria densities and herbivory in an urban forest where the protection of high-value trees and the reduction of environmental contamination are of utmost importance.

IMPACTS OF ROAD DEICING SALT ON THE DEMOGRAPHY OF VERNAL POOL-BREEDING AMPHIBIANS

Deicing agents, primarily road salt, are applied to roads in 26 states in the United States and in a number of European countries, yet the scale of impacts of road salt on aquatic organisms remains largely under-studied. The issue is germane to amphibian conservation because both adult and larval amphibians are known to be particularly sensitive to changes in their osmolar environments. In this study, we combined survey, experimental, and demographic modeling approaches to evaluate the possible effects of road salt on two common vernal-pond-breeding amphibian species, the spotted salamander (Ambystoma maculatum) and the wood frog (Rana sylvatica). We found that in the Adirondack Mountain Region of New York (USA), road salt traveled up to 172 m from the highway into wetlands. Surveys showed that egg mass densities of spotted salamanders (A. maculatum) and wood frogs (R. sylvatica) were two times higher in forest pools than roadside pools, but this pattern was better explained by road proximity than by increased salinity. Experiments demonstrated that embryonic and larval survival were reduced at moderate (500 muS) and high conductivities (3000 muS) in A. maculatum and at high conductivities in R. sylvatica. Demographic models suggest that such egg and larval stage effects of salt may have important impacts on populations near roads, particularly in the case of A. maculatum, for which salt exposure may lead to local extinction. For both species, the effect of road salt was dependent upon the strength of larval density dependence and declined rapidly with distance from the roadside, with the greatest negative effects being limited to within 50 m. Based on this evidence, we argue that efforts to protect local populations of A. maculatum and R. sylvatica in roadside wetlands should, in part, be aimed at reducing application of road salt near wetlands with high conductivity levels.

Relationships between elm spanworm, Ennomos subsignaria, juvenile density and defoliation on mature sycamore maple in an urban environment

Using field surveys, we established sampling procedures for estimating defoliation resulting from elm spanworm, Ennomos subsignaria (Hübner) (Lepidoptera: Geometridae), feeding on mature sycamore maple, Acer pseudoplatanus L. (Aceraceae), in St. John's, Newfoundland and Labrador. We also determined whether densities of E. subsignaria eggs, egg masses, early- or late-instar larvae could predict the amount of defoliation at the end of the larval feeding period. Defoliation estimates acquired by sampling branches from only the lower, mid or upper crown explained ≥80% of the variation in tree-level defoliation, suggesting that density–defoliation relationships established using defoliation data from any crown level would also be useful for predicting tree-level defoliation. In linear regressions, egg and egg mass densities explained ≤20% of variation in defoliation and thus only provide a crude relative estimate of the amount of defoliation that will occur. Early- and late-instar larval density in the lower crown explained 53 and 29%, respectively, of the variation in defoliation in the lower crown, where defoliation levels were highest. Thus monitoring early-instar density in the lower crown should provide pest managers with reliable information for decisions regarding whether to apply suppression tactics while allowing enough time to implement these tactics, if necessary.

Maize planting time and arthropod abundance in southern Mindanao, Philippines. II. Population dynamics of natural enemies

Beneficial arthropods were monitored in monthly plantings over 4 years in a rainfed, triple-maize cropping system in southern Mindanao, Philippines. Generalist predators and two egg parasitoids of the Asian corn borer Ostrinia furnacalis (Guenée) (ACB) did not show significant differences in abundance with respect to calendar month of planting over 39 crops. Two species of Trichogramma (T. evanescens Westwood and T. chilonis Ishii) collectively parasitized 67% of ACB egg masses and 58% eggs over the study becoming more abundant as the crop aged. The closeness of the two parasitism rates suggests that to increase parasitoid efficacy, particularly early in the crop, the best strategy would be augmentation and to increase longevity of wasps by providing carbohydrate sources to extend their searching time. Unparasitized egg masses tended to be smaller showing they were more likely to be overlooked. The ratio between the two parasitoids was 56:44 in favour of the former. Trichogramma evanescens had been introduced 2 years earlier by a government project, whereas T. chilonis probably was introduced by sugarcane estates. Prior to their introduction there were no ACB egg parasitoids in the Philippines and both are firmly established as annual parasitism levels did not continue to rise during the study. Parasitoid activity caused significant reductions in neonate ACB larval numbers beginning 7 weeks after crop emergence in an average crop. Egg parasitism rates were positively and linearly correlated with ACB egg mass density. A quadratic regression model was established between mean egg parasitism rates and egg masses size with peak parasitism rates occurring at 25 eggs per mass. Collectively 32 species of generalist predators averaged 0.9 – 1.5 individuals per plant based on weekly samplings. If ants were excluded, the average dropped to 0.1 – 0.3 per plant. Ants, dominated by Solenopsis geminata (F.), fed on ACB eggs and larvae. Coccinellids as the next most numerous were represented by three species where Micraspis crocea (Mulsant) in particular tracked ACB egg masses and probably the corn leaf aphid Rhopalosiphum maidis (Fitch) as well. Four species of orthropterans also tracked ACB egg masses. The third most abundant guild was 17 spiders with the oxyopid Oxyopes javanus Thorell and the araneid Araneus inustus (C.L. Koch) highly correlated with ACB egg mass densities. Other spiders targeted ACB moths and Atherigona oryzae Malloch adults. The predatory mirid Cyrtorhinus lividipennis Reuter probably targeted the corn leafhopper Cicadulina bimaculata (Evans) and possibly thrips Thrips palmi Karny and Megalurothrips usitatus (Bagnall). The lacewing Chrysopa sp. was abundant late in the crop when aphids were present on tassels.