Oviposition behaviour of Tamarixia radiata: effects of host density and exposure time

1. The number of hosts attacked as a function of host density is considered to be an important characteristic of parasitoid behaviour and is used to estimate key parameters such as handling time and ‘instantaneous rate of discovery’. However, little has been done to validate functional response models by direct observation of parasitoid oviposition behaviour. 2. Tamarixia radiata is the most promising parasitoid for biological control attacking Diaphorina citri. Mass rearing and augmentative release seen as a potential strategy for suppression of D. citri has been documented in abandoned citrus, residential areas, and organic groves. Nevertheless, parasitism rates in culture and in the field are only moderate, leading to questions about oviposition behaviour in response to host density. 3. Behaviours of gravid T. radiata females presented with susceptible host instars were categorised and documented by direct observation for 30 min and by camera recordings made over 12 h. Frequency of searching and antennating increased with host density during the 30 min. Probing rejection rates and search duration increased significantly with host density over 12 h. These factors resulted in significantly lower fecundity than expected, possibly due to host mark‐mediated deterrence within the small searching area. Females took approximately 3.6–4.2 min to probe and parasitise a host regardless of host density and exposure duration. These results were markedly different from the 52.2 min estimated from the functional response equation. 4. Further experiments are required to assess the range and persistence of the putative host‐marking pheromone, and to better understand the relationship between functional response parameters and actual behaviour.     

茶色金龟子和铜色白纹金龟子的初步研究

1.本文所述的两种金龟子,其一为茶色金龟子,属鞘翅目,金龟子科中的Rutelinae亚科,其二为铜色白纹金龟子,属Cetoniinae亚科。 2.茶色金龟子在莲塘一年发生二代。其第1次成虫盛期多在6月。第2次则在8月;铜色白纹金龟子,一年仅发生一代,其成虫出现期为6至9月,少数可延长到10月中旬。 3.茶色金龟子的成虫,为夜出性,傍晚7时半后,即开始出土,停息在多种寄主植物的叶片上,取食或交配,拂晓时飞返土中。铜色白纹金龟子的成虫,为日出性,取食成熟果子,玉米苞穗及多种树木的浆汁,亦喜取食。既钻入后,可连续数日不出。 4.两种金龟子的幼虫,都栖息在土中。茶色金龟子幼虫以在菜园土中、丘陵黄土地及属于粘壤性质的田塍内为多,对于土壤性质选择,较不严格。铜色白纹金龟子幼虫则多集中在腐熟的堆肥及腐殖质极丰富的土中,对于土壤,有比较严格的选择性。 5.关于防治方法:茶色金龟子在成虫期曾试用了0.5％γ体666粉及25％DDT乳剂(1份加水250份〕喷撒,第1种药适用于叶面较粗糙的植物,第2种则可用于叶面较光滑的植物,只要喷撒1次,便能在整个成虫发生期中,避免其飞来取食。铜色白纹金龟子的成虫,则可采用竹筒诱杀,筒高12—16寸,筒内盛腐熟果子及蜜,贴靠枝杆悬挂,能将圆内所有成虫,全部诱入筒中。此外,前一种成虫,并可利用外出     

各种昆虫耐饥力的观察

昆虫耐饥力的强弱,为昆虫的生物学特性之一。对於这个问题,以前还没有人作过系统性的观察。1950—1951两年,我们在这方面,曾经化了一些时间,并已初步得出一些结果,现在把它整理出来,以供大家讨论。     

Soil temperature affects carbon allocation within arbuscular mycorrhizal networks and carbon transport from plant to fungus

How soil carbon balance will be affected by plant–mycorrhizal interactions under future climate scenarios remains a significant unknown in our ability to forecast ecosystem carbon storage and fluxes. We examined the effects of soil temperature (14, 20, 26 °C) on the structure and extent of a multispecies community of arbuscular mycorrhizal (AM) fungi associated with Plantago lanceolata. To isolate fungi from roots, we used a mesh‐divided pot system with separate hyphal compartments near and away from the plant. A ¹³C pulse label was then used to trace the flow of recently fixed photosynthate from plants into belowground pools and respiration. Temperature significantly altered the structure and allocation of the AM hyphal network, with a switch from more vesicles (storage) in cooled soils to more extensive extraradical hyphal networks (growth) in warmed soils. As soil temperature increased, we also observed an increase in the speed at which plant photosynthate was transferred to and respired by roots and AM fungi coupled with an increase in the amount of carbon respired per unit hyphal length. These differences were largely independent of plant size and rates of photosynthesis. In a warmer world, we would therefore expect more carbon losses to the atmosphere from AM fungal respiration, which are unlikely to be balanced by increased growth of AM fungal hyphae.     

The provision of winter bird food by the English Environmental Stewardship scheme

Environmental Stewardship (ES) is the main mechanism for reversing the decline in farmland birds in England, and includes a range of options designed to provide winter foraging for seed‐eating species. We estimated granivorous songbird densities on ES options designed to provide winter food, on farms within the Entry Level (ELS) or Higher Level (HLS) strata of ES. ES Wild Bird Mixtures (WBMs) hosted higher densities and a wider range of granivores than non‐ES game covers, although in East Anglia the enhanced HLS WBM was used no more than the basic ELS WBM. In the West Midlands there were low densities of granivores on all WBMs and game covers. The widespread ELS WBM appeared to provide little food for buntings but supported finches, partially through greater weed burdens. There was a weak, non‐significant trend for Skylarks Alauda arvensis to make greater use of ELS cereal stubbles than non‐ES stubbles, possibly because of post‐harvest herbicide restrictions allowing overwinter weed growth. At the field scale, this work demonstrates that although some ES options provide winter food resources for birds, there is limited evidence for additional benefits of Higher Level vs. Entry Level Stewardship to wintering farmland songbirds.     

Eucalyptus leachate inhibits reproduction in a freshwater fish

1. Dissolved organic carbon (DOC) can induce lethal and sub‐lethal effects in exposed biota via hypoxic blackwater events and the toxicity of leached compounds. Little is known of how DOC exposure affects fish reproduction despite the fact that its release can coincide with spawning‐associated flow pulses. 2. River red gum (Eucalyptus camaldulensis) leaf leachate is a major source of DOC in Australian freshwaters and includes the toxic plant secondary metabolites polyphenols and tannins. High concentrations of leachate are released when leaves on floodplains or dry stream channels are inundated by water. 3. Southern pygmy perch (Nannoperca australis) from naturally high and naturally low Eucalyptus leachate environments in south‐east Australia were exposed to elevated leachate levels to investigate the effects of DOC on reproduction and to explore whether response patterns were consistent with populations becoming locally adapted to historical leachate levels. 4. Fish exposed to leachate were half as likely to reach sexual maturity as control fish. Fish from a naturally high‐exposure population tended to reach sexual maturity earlier than those from a naturally low‐exposure population. Leachate exposure had no effect on either egg size or fecundity. 5. Our results suggest that leachate‐exposed mothers did not reproduce because they were physiologically stressed or perceive the environment to be unsuitable, which raises the potential of plastic or adaptive responses to this stressor. The negative sub‐lethal effects observed have important fitness implications for individuals, the viability of populations and the management of environmental flows and riparian zones.