The relative effects of local management and landscape context on weed seed predation and carabid functional groups

Farmland biodiversity and its associated ecosystem services are affected by agricultural activities at multiple spatial scales. Among these services, the regulation of weeds by invertebrate seed predators has received much attention recently but little is known about the relative effect of local management and landscape context of fields on this process. We monitored seed predation on four common weed species and carabid communities in 28 winter-cereals fields during five consecutive weeks in spring 2010. These fields were situated in contrasted landscape contexts and varied in terms of intensity of pesticide treatments and soil tillage regimes. Weed seed predation was strongly and positively related to the Shannon diversity of (strictly) granivorous carabids and to the activity–density of omnivorous carabids but negatively to the richness of omnivorous carabids. Weed seed predation and granivore diversity were positively related to landscape diversity and the proportion cover of temporary grassland within a 1000 m radius around focal fields and were negatively affected by the intensity of local pesticide treatments. No-till systems sheltered higher diversity of granivorous carabids but did not show higher seed predation rates. We showed that landscape composition factors had a higher relative influence than local practices factors on weed seed predation service. Consequently, weed management strategies should not only consider the management of single fields but also the surrounding landscape to preserve carabid biodiversity and enhance weed seed predation service.     

Toward a practical use of Neotropical odonates as bioindicators: Testing congruence across taxonomic resolution and life stages

Odonates are suggested as bioindicators of human impact. However, their complex life cycles add additional challenges in the practical use as bioindicators, because the level of taxonomic identification could be dependent on life-history stage and, during their ontogeny, dramatic changes occur in their niche (ontogenetic niche shifts). Considering that larvae and adults have different biological characteristics, which could interfere in their performance as bioindicators, we first sought to understand how similar or different environmental factors affect larval and adult life stages in the Odonata. Second, we assessed the level of congruence between (larvae and adult) and within (adult genera and species) life-history stages, considering the taxonomic and numerical resolution. We sampled larvae and adults in 44 streams distributed along a riverine network in southwest Brazil. Larvae samples constituted 20 sampling units of 1 m length each, using the kick sampling method; adults were collected for 1 h at each site with a hand net along a 100-m transect parallel to the stream/river banks. The influence of environmental factors on larvae and adult was assessed by redundancy analysis coupled with forward selection. The congruence level between response matrices was determined by Procrustes analysis. Our results revealed that a set of environmental variables explained a portion of larvae and adults distribution and some environmental factors affect both between (larvae and adults) and within (adult genera and species) life-history stages. Larvae and adult were about 54% congruent, regardless of taxonomic level of adults. Abundance of adult genera and species were 94% congruent, but numerical resolution (abundance vs. incidence) decreased the congruency by 10%. Environmental variables could influence larvae and adults individually or via carry-over effects, i.e., larval environmental conditions that could affect adult fitness components or vice versa. In addition, some odonate behaviors, such as female selection of more appropriate habitats for laying their eggs, could also help us to explain our results, because it could determine larvae distribution. In a biomonitoring perspective, considering the cost-benefit of taxonomic level and sampling of larvae and adults, our results suggest that abundance of adult genera could be used in biomonitoring programs since they capture, respectively, 94% and 54% of the information carried by adult species and larvae.     

Development of permethrin resistance in Culex quinquefasciatus Say in Kuala Lumpur,Malaysia

The resistance status towards permethrin among the laboratory strain, the permethrin-selected strain and four field strains of Culex quinquefasciatus collected in Kuala Lumpur, Malaysia was determined using three standard laboratory methods: WHO larval bioassay, WHO adult bioassay and biochemical microplate assay. Cx. quinquefasciatus permethrin-selected strain larvae were the least susceptible to permethrin with a resistance ratio of 47.28-folds, whereas all field strain larvae of the same species were tolerant to permethrin with resistance ratios of more than 3-folds. In contrast, in adult stage, the permethrin exposed permethrin-selected strain (resistance ratio = 1.27) was found to be more susceptible to permethrin than all permethrin-exposed field strains (resistance ratios = 2.23–2.48). Complete mortalities for all strains of Cx. quinquefasciatus adults proved the effectiveness of the synergist; piperonyl butoxide (PBO). For the biochemical microplate assay, the reduction of the mean optical density of elevated oxidase activity of three field strains upon exposure to PBO confirmed the association between oxidase activity and permethrin tolerance. On the other hand, irregular patterns of the mean optical density of elevated oxidase activity in the laboratory strain, permethrin-selected strain and Jalan Fletcher strain illustrated the gene variation within these mosquito colonies as well as the involvement of other enzyme activities in the permethrin resistance occurred.     

Tillage effects on carbon footprint and ecosystem services of climate regulation in a winter wheat–summer maize cropping system of the North China Plain

Inappropriate farm practices can increase greenhouse gases (GHGs) emissions and reduce soil organic carbon (SOC) sequestration, thereby increasing carbon footprints (CFs), jeopardizing ecosystem services, and affecting climate change. Therefore, the objectives of this study were to assess the effects of different tillage systems on CFs, GHGs emissions, and ecosystem service (ES) values of climate regulation and to identify climate-resilient tillage practices for a winter wheat (Triticum aestivum L.)-summer maize (Zea mays L.) cropping system in the North China Plain (NCP). The experiment was established in 2008 involving no-till with residue retention (NT), rotary tillage with residue incorporation (RT), sub-soiling with residue incorporation (ST), and plow tillage with residue incorporation (PT). The results showed that GHGs emissions from agricultural inputs were 6432.3–6527.3 kg CO₂-eq ha⁻¹ yr⁻¹ during the entire growing season, respectively. The GHGs emission from chemical fertilizers and irrigation accounted for >80% of that from agricultural inputs during the entire growing season. The GHGs emission from agricultural inputs were >2.3 times larger in winter wheat than that in the summer maize season. The CFs at yield-scale during the entire growing season were 0.431, 0.425, 0.427, and 0.427 without and 0.286, 0.364, 0.360, and 0.334 kg CO₂-eq kg⁻¹ yr⁻¹ with SOC sequestration under NT, RT, ST, and PT, respectively. Regardless of SOC sequestration, the CFs of winter wheat was larger than that of summer maize. Agricultural inputs and SOC change contributed mainly to the component of CFs of winter wheat and summer maize. The ES value of climate regulation under NT was ¥159.2, 515.6, and 478.1 ha⁻¹ yr⁻¹ higher than that under RT, ST, and PT during the entire growing season. Therefore, NT could be a preferred “Climate-resilient” technology for lowering CFs and enhancing ecosystem services of climate regulation for the winter wheat–summer maize system in the NCP.     

Unravelling the process of weed seed predation: Developing options for better weed control

Seed predation can cause significant losses of weed seeds in agricultural systems and can, thus, contribute to weed control. The removal of Lolium multiflorum and Vicia villosa seeds by harvester ants, Messor barbarus, and granivorous rodents, Mus spretus, in six cereal fields in NE Spain was separated into three sequential processes, namely (1) the probability of finding a seed cache (cache encounter rate), (2) the percentage of seeds utilized once a seed cache has been found (seed exploitation rate) and (3) seed selection if multiple species are present (preference). Identifying the most important behavioural component and factors that drive it may help to better understand and manage seed predation.Seed cache encounter rate correlated well with overall seed removal rate caused by harvester ants (r² = 0.91), or rodents (r² = 0.82). Once found, seed exploitation rates were high and fairly constant from spring to autumn for harvester ants, and low throughout the season for rodents. Harvester ants removed almost all L. multiflorum seeds from caches found, while the exploitation of V. villosa seeds varied across the season. In the case of rodents, cache encounter rate, but not exploitation rate, could be explained by canopy cover provided by the crop. L. multiflorum seemed to be preferred in early 2007, whereas V. villosa was in 2008.The adoption of no-till or minimum tillage systems together with the establishment of field edge vegetation are likely to encourage seed cache encounter and exploitation rates by both harvester ants and rodents, thus leading to increased weed control in semi-arid cereals.     

Food consumption,utilization and ecological efficiency of Parthenium beetle,Zygogramma bicolorata pallister (Coleoptera: Chrysomelidae)

Food consumption, utilization and ecological efficiency of Zygogramma bicolorata were studied in larvae and adults up to 45 days old. The study revealed that sex had a significant influence on dry food consumption in adults but not in larvae. The other parameters of ecological efficiencies, viz. efficiency of conversion of ingested food (E.C.I.), tissue growth and dry biomass, were highest in the fourth instar and in adult females. The Consumption Index (C.I.) was higher in males than females in both larval and adult stages. Developmental and growth rates were relatively higher in the first and second instars. The fourth instar and adult females were the most efficient consumers and converters of food. Food intake by females was an important determinant of the number of eggs laid.     

Delayed efficacy of Beauveria bassiana foliar spray applications against Colorado potato beetle: Impacts of number and timing of applications on larval and next-generation adult populations

Spray programs comprising multiple or single foliar applications of the fungal pathogen Beauveria bassiana strain GHA (Bb-GHA) made during morning (AM) vs. evening (PM) hours were tested against Colorado potato beetle Leptinotarsa decemlineata (CPB) in small research plots of potatoes over multiple field seasons, and efficacy against larval and first-generation adult populations was evaluated. The pathogen (formulated as BotaniGard WP®) was applied at the rate of 2.5 × 10¹³ conidia in a spray volume of 468–480 L per ha. Modes of efficacy were investigated by collecting pre-pupal larvae and holding them in soil cages in the field and laboratory. Results revealed that larval control achievable with multiple-spray programs was poor regardless of environmental moisture conditions, but that emerging adult populations were reduced by an average of 80% (range 58–93%) relative to control populations. Programs comprising a single application of Bb targeted against late-instar larvae reduced adult populations by an average of 60% (range 36–75%). Overall mean differences in efficacy of PM vs. AM applications were not significant in terms of larval control and defoliation damage. Emergence of next-generation adults was significantly lower in the PM vs. AM treatments, but differences were small in terms of percent control. Average yields from the Bb-GHA multiple-spray programs were 18% greater than those from the controls; the mean 5% increase resulting from the Bb-GHA single-spray programs was not significant. Observations indicated that moderate to high rates of inoculation and infection were achieved under a broad range of environmental conditions in the crop canopy, but larvae persisted until they entered the soil to pupate. Most deaths due to mycosis occurred among pre-pupal larvae in their pupation cells in the soil. These results, in combination with similar findings of delayed efficacy reported by other researchers, indicate that foliar applications of Bb could be a significant component of an IPM program aimed at suppressing CPB populations on large farms or over large areas.     

陕北黄土丘陵沟壑区水土保持耕作及施肥下农田土壤种子库特征

为了探明多年免耕下农田恶性杂草发生的机理,提高保护性耕作下作物对农田恶性杂草持久稳定的抑制效果,依据陕西安塞田间4a的定位试验, 采用小区调查取样和室内实验相结合的方法,从物种组成、密度特征、多样性以及相似性特征等方面,研究了黄土丘陵旱作农区大豆(Glycine max)、玉米(Zea mays)、红小豆(Semen Phaseoli)、马铃薯(Solanum tuberosum)在翻耕化肥(CF)、翻耕有机肥(CM)、翻耕无肥(CN)、免耕化肥(NF)、免耕有机肥(NM)、免耕无肥(NN)等水平下的农田土壤种子库.结果表明: (1) 4种作物24种土样中共萌发出12个物种1965株幼苗,隶属于7科12属.1年生杂草占94%,棒头草(fugax nees ex steud)、苋菜(Acalypha australis)、马唐(Digitaria sanguinalis)、早熟禾(Poa sphondylodes)为优势种,占87%.(2)在0～20cm土层不同处理间,土壤种子库的密度变动于(282.9±63.4)～(7482.5±1078.3)粒·m- 2,其中,红小豆小区＞马铃薯小区＞大豆小区＞玉米小区;翻耕小区＞免耕小区;有机肥小区＞化肥小区＞无肥小区,差异极显著. (3)土壤种子库密度NM红小豆最高,NN玉米最低;丰富度指数CF大豆为2.30;NN红小豆为0.29;多样性指数NN大豆为5.56,CF红小豆为0.45;生态优势度NF玉米为1.35,CF大豆为0.17.玉米、大豆是黄土丘陵沟壑旱作农区免耕下农田抑制杂草最为适宜的作物, NM玉米、NF大豆和NM大豆是黄土丘陵沟壑旱作农区较优的耕作管理方式,其农田的生态效应是能够竞争性抑制恶性杂草的蔓延,优化土壤环境,杂草的多样性高且比较均衡,杂草的土壤种子库密度低.     

Direct effects of tillage on the activity density of ground beetle (Coleoptera: Carabidae) weed seed predators

Ground beetles are well known as beneficial organisms in agroecosystems, contributing to the predation of a wide range of animal pests and weed seeds. Tillage has generally been shown to have a negative effect on ground beetles, but it is not known whether this is because of direct mortality or the result of indirect losses resulting from dispersal caused by habitat deterioration. In 2005, field experiments measured direct, tillage-induced mortality, of four carabid weed seed predators, Harpalus rufipes DeGeer, Agonum muelleri Herbst, Anisodactylus merula Germar, and Amara cupreolata Putzeys, and one arthropod predator, Pterostichus melanarius Illiger, common to agroecosystems in the northeastern United States. Three tillage treatments (moldboard plow, chisel plow, and rotary tillage) were compared with undisturbed controls at two sites (Stillwater and Presque Isle) and at two dates (July and August) in Maine. Carabid activity density after disturbance was measured using fenced pitfall traps installed immediately after tillage to remove any effects of dispersal. Rotary tillage and moldboard plowing reduced weed seed predator activity density 52 and 54%, respectively. Carabid activity density after chisel plowing was similar to the undisturbed control. This trend was true for each of the weed seed predator species studied. However, activity density of the arthropod predator P. melanarius was reduced by all tillage types, indicating a greater sensitivity to tillage than the four weed seed predator species. These results confirm the need to consider both direct and indirect effects of management in studies of invertebrate seed predators.     

A comparison on ecosystem services before/after “5.12” Wenchuan earthquake

Earthquake has great potential to destroy vegetation and water resources. Here, we estimated the ecosystem services before/after “5.12” Wenchuan earthquake in China, in the center zone (ca. 24, 696.94 km²) of the earthquake, the destroyed service value approximately 520.04 × 10⁶ $. Moreover, the losses of biodiversity conservation value were inestimable in this earthquake. The results suggested that earthquake can seriously damage service function of ecosystem. It is a nice opportunity for ecologists to study the recovery of ecosystem services after earthquake disturbance.     

Host suitability and fitness-related parameters of Campoletis sonorensis (Hymenoptera: Ichneumonidae) as a parasitoid of the cabbage looper,Trichoplusia ni (Lepidoptera: Noctuidae)

The seven age-classes of Trichoplusia ni (Hübner) larvae evaluated in this study as hosts of Campoletis sonorensis indicates that early 2nd larval instar (3–5 day-old larvae) of T. ni represents the most suitable host stage for the development of the larval endoparasitoid C. sonorensis. The higher suitability of early 2nd larval instar of T. ni resulted in more parasitised larvae, a higher rate of successful parasitoid emergence, a higher rate of female progeny, and a lower rate of immature parasitoid mortality. The fitness gain of C. sonorensis on late 1st larval instar (2 day-old larvae) and late 2nd larval instar –early 3rd instars (6–8 day-old larvae) stages of T. ni is negatively affected by the trade-offs between the different physiological and behavioral characteristics influencing their suitability as hosts of C. sonorensis.     

Stage- and sex-specific heat tolerance in the yellow dung fly Scathophaga stercoraria

Thermal tolerance varies at all hierarchical levels of biological organization: among species, populations, individuals, and even within individuals. Age- or developmental stage- and sex-specific thermal effects have received relatively little attention in the literature, despite being crucial for understanding thermal adaptation in nature and responses to global warming. We document stage- and sex- specific heat tolerance in the yellow dung fly Scathophaga stercoraria (Diptera: Scathophagidae), a species common throughout the northern hemisphere that generally favours cool climates. Exposure of eggs to temperatures up to 32 °C did not affect larval hatching rate, but subsequent egg-to-adult survival at a benign temperature was reduced. Permanent transfer from benign (18 °C) to hot temperatures (up to 31 °C) at different larval and pupal stages strongly decreased egg-to-adult survival, though survival continuously improved the later the transfer occurred. Temporary transfer for only two days increased mortality more weakly, survival being lowest when temperature stress was imposed early during the larval or pupal stages. Adult flies provided with sugar and water tolerated 31 °C longer than previously thought (5 days in males to 9 days in females). Eggs were thus less susceptible to thermal stress than larvae, pupae or adults, in agreement with the hypothesis that more mobile stages require less physiological protection against heat because they can behaviourally thermoregulate. The probability of mating, of laying a clutch, and hatching success were generally independently reduced by exposure of females or males to warm temperatures (24 °C) during the juvenile or adult stages, with some interactions evident. High temperature stress thus affects survival differentially depending on when it occurs during the juvenile or the pre-reproductive adult life stage, and affects reproductive success via the mating behaviour of both sexes, female physiology in terms of oviposition, and fertility via sperm and/or egg quality. Our results illustrate that temperature stress, even when moderate and temporary, during early development can have profound lethal and non-lethal fitness-consequences later in life.     

Long-term tillage effects on soil organic carbon and dissolved organic carbon in a purple paddy soil of Southwest China

The impact of conservation tillage practices on soil carbon has been of great interest in recent years. Conservation tillage might have the potential to enhance soil carbon accumulation and alter the depth distribution of soil carbon compared to conventional tillage based systems. Changes in the soil organic carbon (SOC) as influenced by tillage, are more noticeable under long-term rather than short-term tillage practices. The objective of this study was to determine the impacts of long-term tillage on SOC and dissolved organic carbon (DOC) status after 19 years of four tillage treatments in a Hydragric Anthrosol. In this experiment four tillage systems included conventional tillage with rotation of rice and winter fallow system (CTF), conventional tillage with rotation of rice and rape system (CTR), no-till and ridge culture with rotation of rice and rape system (NT) and tillage and ridge culture with rotation of rice and rape system (TR). Soils were sampled in the spring of 2009 and sectioned into 0–10, 10–20, 20–30, 30–40, 40–50 and 50–60 cm depth, respectively.Tillage effect on SOC was observed, and SOC concentrations were much larger under NT than the other three tillage methods in all soil depths from 0 to 60 cm. The mean SOC concentration at 0–60 cm soil depth followed the sequence: NT (22.74 g kg^?1) > CTF (14.57 g kg^?1) > TR (13.10 g kg^?1) > CTR (11.92 g kg^?1). SOC concentrations under NT were significantly higher than TR and CTR (P < 0.01), and higher than CTF treatment (P < 0.05). The SOC storage was calculated on equivalent soil mass basis. Results showed that the highest SOC storage at 0–60 cm depth presented in NT, which was 158.52 Mg C ha^?1, followed by CTF (106.74 Mg C ha^?1), TR (93.11 Mg C ha^?1) and CTR (88.60 Mg C ha^?1). Compared with conventional tillage (CTF), the total SOC storage in NT increased by 48.51%, but decreased by 16.99% and 12.77% under CTR and TR treatments, respectively. The effect of tillage on DOC was significant at 0–10 cm soil layer, and DOC concentration was much higher under CTF than the other three treatments (P < 0.01). Throughout 0–60 cm soil depth, DOC concentrations were 32.92, 32.63, 26.79 and 22.10 mg kg^?1 under NT, CTF, CTR and TR, and the differences among the four treatments were not significant (P > 0.05). In conclusion, NT increased SOC concentration and storage compared to conventional tillage operation but not for DOC.     

不同虫态及虫龄大草蛉与七星瓢虫之间的集团内互作

【目的】为明确新疆棉田棉蚜 Aphis gossypii 捕食性天敌之间的集团内捕食效应及其对蚜虫数量的控制作用。【方法】本研究以优势天敌昆虫大草蛉 Chrysopa pallens 和七星瓢虫 Coccinella septempunctata 为对象,以棉蚜为猎物,在温室中利用盆栽棉花,首先观察了2种天敌昆虫之间各虫态及虫龄配对的19个处理在无蚜植株上共存24 h后的存活数,然后观察了2种天敌昆虫配对处理下棉苗上棉蚜数量随时间的变化趋势。【结果】在无蚜棉株上2种捕食性天敌昆虫共存24 h后的存活结果表明：（1）在发育阶段相同的配对组合中,若是成虫则均存活,若是１龄幼虫则大草蛉存活较多,若是末龄幼虫则七星瓢虫存活较多;（2）在有卵的组配中,除七星瓢虫卵不被大草蛉成虫所捕食外,其他5个组配处理中卵均被捕食;（3）在有蛹的配对组合中,除七星瓢虫蛹被大草蛉末龄幼虫捕食外,其他处理下蛹均不被捕食;（4）在成虫与幼虫的配对组合中,七星瓢虫成虫捕食较多的大草蛉1龄幼虫,但不捕食大草蛉末龄幼虫,而大草蛉成虫与七星瓢虫1龄或末龄幼虫之间不发生捕食;(5）在不同龄期幼虫的配对组合中,大草蛉末龄幼虫捕食七星瓢虫1龄幼虫,而七星瓢虫末龄幼虫捕食大草蛉1龄幼虫。在有蚜植株上2种捕食性天敌共存对棉蚜数量具有不同的控制作用：（1）2种捕食昆虫的幼虫各自单独存在（对照）下,蚜虫密度随时间而降低;（2）大草蛉幼虫与七星瓢虫幼虫或成虫配对处理下,棉蚜密度随时间而增大;（3）大草蛉成虫与七星瓢虫幼虫或成虫配对处理下,棉蚜密度随时间而减小。【结论】研究结果说明,大草蛉与七星瓢虫之间存在集团内捕食,但２种天敌共存对棉蚜的控制作用取决于大草蛉虫态, 若大草蛉为幼虫,可使蚜虫密度增大,若为成虫,则使蚜虫密度减小。     

Incorporating sheep into dryland grain production systems: II. Impact on changes in biomass and weed density

Weed control in fallow management to conserve soil moisture and nutrients is the largest variable cost to dryland grain production. Our objective was to compare burning, grazing, tilling, trampling and clipping wheat stubble fields on changes in total aboveground biomass and weed density. Treatments were evaluated in three experiments using a randomized complete block design for each experiment with four replications at each site. Contrasts statements were used to make pre-planned comparisons. For experiment 1, treatments were fall tilled, fall grazed, spring grazed, fall and spring combined (Fall/Spr) grazed, and an untreated control. For grazing treatments, five mature ewes were confined with electric fence to 111 m² plot for 24 h for fall and spring resulting in a stocking rate of 452 sheep day/ha. For Fall/Spr the stocking rate was 904 sheep day/ha. For experiment 2, treatments were fall grazed, fall burned, fall tilled, and an untreated control. In experiment 3, treatments were fall trampling by sheep, spring trampling by sheep, fall and spring combined (Fall/Spr) trampling by sheep, stubble hand clipped to a height of 4.5 cm, and an untreated control. Trampling treatments were applied at the same stocking rates as grazing treatments but sheep were muzzled to prevent intake. Data were collected in the fall, prior to treatment imposition, and spring, after treatments had been removed. Post treatment biomass and weed density were greater (P < 0.05) in either control or tilled plots when compared to grazed plots. Post treatment biomass and weed density were greater (P < 0.01) for control than burned plots. Post treatment biomass, weed density, and percent change in these variables, did not differ (P > 0.08) between burned and tilled, and burned and grazed treatments. These results indicate the potential for using grazing sheep as a component in fallow management to reduce biomass and control weeds.     

Morphological abnormalities and lethality in silkworm (Bombyx mori) larvae treated with high concentrations of insect growth-blocking peptide

Insect growth-blocking peptides (GBPs) exhibit growth-blocking and paralytic activity. Low concentrations of GBP stimulate larval growth, whereas high concentrations of GBP significantly retard larval growth. Here, we show that morphological abnormalities and lethality were induced in silkworm (Bombyx mori) larvae by high concentrations of GBP. Active B. mori GBP (BmGBP) was produced by treating recombinant proBmGBP (expressed in baculovirus-infected insect cells) with bovine factor Xa. When silkworm larvae on day 1 of the fifth-instar stage were injected between the seventh and eight abdominal segments with BmGBP (100 or 500 ng/larva), the larval–pupal and pupal–adult transformations of these silkworms were delayed in a dose-dependent manner. However, a high concentration (2000 ng/larva) of BmGBP or Spodoptera exigua GBP (SeGBP) acutely induced morphological abnormalities and death in silkworm larvae. In silkworm larvae treated with high concentrations of GBPs, the ingested food excessively accumulated in the foregut, which caused extreme swelling in both the thorax and the foregut and resulted in larval death. Therefore, these results not only provide insight into the effect of insect GBPs on gut physiology but also reveal a novel function of insect GBPs.     

Lethal effects of ichthyotoxic raphidophytes,Chattonella marina,C. antiqua,and Heterosigma akashiwo,on post-embryonic stages of the Japanese pearl oyster,Pinctada fucata martensii

The inimical effects of the ichthyotoxic harmful algal bloom (HAB)-forming raphidophytes Heterosigma akashiwo, Chattonella marina, and Chattonella antiqua on the early-life stages of the Japanese pearl oyster Pinctada fucata martensii were studied. Fertilized eggs and developing embryos were not affected following exposure to the harmful raphidophytes; however, all three algal species severely affected trochophores and D-larvae, early-stage D-larvae, and late-stage pre-settling larvae. Exposure to C. marina (5 × 10² cells ml⁻¹), C. antiqua (10³ cells ml⁻¹), and H. akashiwo (5 × 10³ cells ml⁻¹) resulted in decreased success of metamorphosis to the trochophore stage. A complete inhibition of trochophore metamorphosis was observed following exposure to C. antiqua at 5 × 10³ cells ml⁻¹ and C. marina at 8 × 10³ cells ml⁻¹. In all experiments, more than 80% of newly formed trochophores were anomalous, and in the case of exposure to H. akashiwo at 10⁵ cells ml⁻¹ more than 70% of D-larvae were anomalous. The activity rates of D-larvae (1-day-old) were significantly reduced following exposure to C. antiqua (8 × 10³ cells ml⁻¹, 24 h), C. marina (8 × 10³ cells ml⁻¹, 24 h), and H. akashiwo (10⁴ cells ml⁻¹, 24 h). The activity rates of pre-settling larvae (21-day-old) were also significantly reduced following exposure to C. antiqua (10³ cells ml⁻¹, 24 h), C. marina (8 × 10³ cells ml⁻¹, 24 h), and H. akashiwo (5 × 10⁴ cells ml⁻¹, 24 h). Significant mortalities of both larval stages were induced by all three raphidophytes, with higher mortality rates registered for pre-settling larvae than D-larvae, especially following exposure to C. marina (5 × 10²–8 × 10³ cells ml⁻¹, 48–86 h) and C. antiqua (10³–8 × 10³ cells ml⁻¹, 72–86 h). Contact between raphidophyte cells and newly metamorphosed trochophores and D-larvae, 1-day-old D-larvae, and 21-day-old larvae resulted in microscopic changes in the raphidophytes, and then, in the motile early-life stages of pearl oysters. Upon contact and physical disturbance of their cells by larval cilia, H. akashiwo, C. marina and C. antiqua became immotile and shed their glycocalyx. The trochophores and larvae were observed trapped in a conglomerate of glycocalyx and mucus, most probably a mixture of larval mucous and raphidophyte tricosyts and mucocytes. All motile stages of pearl oyster larvae showed a typical escape behavior translating into increased swimming in an effort to release themselves from the sticky mucous traps. The larvae subsequently became exhausted, entrapped in more heavy mucous, lost their larval cilia, sank, become immotile, and died. Although other toxic mediators could have been involved, the results of the present study indicate that all three raphidophytes were harmful only for motile stages of pearl oysters, and that the physical disturbance of their cells upon contact with the ciliary structures of pearl oyster larvae initiated the harmful mechanism. The present study is the first report of lethal effects of harmful Chattonella spp. towards larvae of a bivalve mollusc. Blooms of H. akashiwo, C. antiqua and C. marina occur in all major cultivation areas of P. fucata martensii during the developmental period of their larvae. Therefore, exposure of the motile early-life stages of Japanese pearl oysters could adversely affect their population recruitment. In addition, the present study shows that further research with early-life development of pearl oysters and other bivalves could contribute to improving the understanding of the controversial harmful mechanisms of raphidophytes in marine organisms.     

Potential for integrated control of Culex quinquefasciatus (Diptera: Culicidae) using larvicides and guppies

Acute toxicity tests were carried out to determine the effect of three larvicides, spinosad, pirimiphos methyl, and chlorpyrifos, on Culex quinquefasciatus Say, Anopheles gambiae s.s. Giles (Diptera: Culicidae), and guppies, Poecilia reticulata Peters (Pisces: Poeciliidae). Thereafter, larvae of Cx. quinquefasciatus were introduced to P. reticulata in containers of different volumes with low concentrations of each larvicide at established predator to prey densities of 1–35; 5–70 and 10–350 (fish to larvae) respectively. The experiment was replicated six times, and the larval consumption was counted after 24 h. Spinosad and pirimiphos methyl were significantly toxic to Cx. quinquefasciatus, the less susceptible mosquito species. Guppy consumption of Culex larvae was highest at a predator to prey density 5–70. Feeding activity of guppies increased in the spinosad treatment at 49 μg L⁻¹ compared to control and the synthetic larvicides. The synthetic larvicides generally reduced consumption of larvae except for the lowest concentration of pirimiphos methyl which increased it at the highest predator to prey density in a 3 L container. The highest percentage of Culex larvae was consumed by fish in the presence of spinosad at 49 μg L⁻¹ and a predator to prey density of 5–70 in 0.5 L plastic containers. Thus, predator to prey density, container size, type and concentration of larvicide are all important factors to be considered in integrated management of mosquito larvae.     

Attraction of the predator,Harmonia axyridis (Coleoptera: Coccinellidae), to its prey,Myzus persicae (Hemiptera: Aphididae), feeding on Chinese cabbage

The predatory multicolored Asian lady beetle, Harmonia axyridis, was attracted to volatiles released from Chinese cabbage infested by the green peach aphid, Myzus persicae, in T-tube olfactometer choice tests. However, lady beetle adults and larvae did not respond to clean air, Chinese cabbage alone or green peach aphid alone. Of different prey densities, H. axyridis adults were most attracted to Chinese cabbage infested by 60 M. persicae adults after 24 h. However, H. axyridis larvae were not attracted to Chinese cabbage infested by M. persicae. Mechanically damaged Chinese cabbage attracted neither lady beetle adults nor larvae. Predatory adults were attracted to 60 M. persicae adults after 24 and 48 h, and to 90 M. persicae adults after 12 h, suggesting that the predatory response depends on the prey density. Lady adult beetles did not prefer the volatiles induced by Diamondback moth, Plutella xylostella, indicating that specific host insect specificity attracts respective natural enemies. It can be explained that the volatile compounds emitted from the host plant as a result of herbivore attack preferred by the specific insect species.     

Effects of temperature on embryonic and early larval growth and development in the rough-skinned newt (Taricha granulosa)

We investigated the effects of temperature on the growth and development of embryonic and early larval stages of a western North American amphibian, the rough-skinned newt (Taricha granulosa). We assigned newt eggs to different temperatures (7, 14, or 21 °C); after hatching, we re-assigned the newt larvae into the three different temperatures. Over the course of three to four weeks, we measured total length and developmental stage of the larvae. Our results indicated a strong positive relationship over time between temperature and both length and developmental stage. Importantly, individuals assigned to cooler embryonic temperatures did not achieve the larval sizes of individuals from the warmer embryonic treatments, regardless of larval temperature. Our investigation of growth and development at different temperatures demonstrates carry-over effects and provides a more comprehensive understanding of how organisms respond to temperature changes during early development.