Suitability of some Lantana camara varieties as host plants for the root-feeding flea beetle, Longitarsus bethae

Compatibility between the root-feeding agent Longitarsus bethae Savini & Escalona and the varieties of the target weed Lantana camara L. could influence the chances of successful establishment and effectiveness of this agent as a biocontrol agent of lantana in South Africa. Laboratory experiments were conducted to determine the influence of major South African lantana varieties on feeding, colonization, oviposition preference and larval survival of L. bethae. Feeding preference and the number of adults per plant varied among the varieties. The most damaged and colonized varieties were 150 Orange, 009 Light Pink and 113 Dark Pink. Variety 018 Dark Pink was the least damaged, while 021 Total Pink and 029 White Pink were the least colonized. Females laid the highest number of eggs on variety 150 Orange. The lowest number of eggs was recorded on Australian Richmond Pink and the closely related species Lippia wilmsii. Larval survival differed significantly among the varieties. The highest survival was recorded on 150 Orange. Duration of development also varied significantly among the varieties, with the slowest rate of development recorded on variety 029 Light Pink and the quickest on variety 015 White Yellow. Although variations in female body size were less significant among varieties, males emerging from variety 150 Orange were slightly smaller than those emerged from other varieties. There was a significant tendency for females to select varieties that enhanced the survival of their offspring, which met the predictions of the preference-performance hypothesis. The data suggest that the chances of establishment and successful control of the weed are expected to be much greater on those varieties that were preferred for oviposition and provided better larval performance.     

补充非寄主食物对芙新姬小蜂和潜蝇姬小蜂控害行为权衡的影响

芙新姬小蜂和潜蝇姬小蜂均为强卵育型(synovigenic)寄生蜂,成虫具有产卵寄生致死、寄主取食致死和寄主叮蛰直接致死3种寄主致死行为。为了明确成虫补充非寄主食物营养对2种姬小蜂控害潜力/控害行为的影响,本文比较研究了分别提供寄主食物和寄主食物+非寄主食物(10%葡萄糖)条件下的2种姬小蜂在初羽化前期(前6 d)内对美洲斑潜蝇幼虫的致死行为的影响。结果显示:在仅提供寄主食物时,芙新姬小蜂的寄生、取食和总体致死量均显著的高于潜蝇姬小蜂,但是直接致死能力却弱于后者;补充非寄主食物和仅提供寄主食物处理相比,两种寄生蜂的寄生量,取食量和总致死量均呈下降趋势。该研究显示:在初羽化前期,取食寄主食物的雌蜂比取食寄主食物+葡萄糖的雌蜂具有更强的致死能力。     

蜜粉源植物对天敌昆虫的作用及其在生物防治中的应用

寄生性和捕食性天敌昆虫成虫普遍存在通过取食蜜粉源植物补充营养的行为,这可不同程度地促进天敌昆虫性成熟、延长其寿命、提高其生殖力或寄生率,以及搜寻寄主效率和子代雌性比率,从而显著提高天敌昆虫在生物防治中的控害能力和效果。蜜粉源植物花的结构及植物对天敌昆虫产生的嗅觉、视觉信号和花蜜花粉对天敌昆虫产生的味觉信号又显著影响天敌昆虫选择蜜粉源植物的行为和结果。但是,蜜粉源植物也可成为害虫的补充营养植物,从而提高害虫的为害能力。因此,需深入研究不同蜜粉源植物对天敌昆虫及害虫的作用,趋利避害,才可能应用蜜粉源植物成功调控天敌与害虫的益害比,实现害虫的可持续控制。     

An optimal foraging and migration model for juvenile plaice

Summary A state-dependent model has been used to predict daily and tidal patterns of migration, feeding and inactivity in juvenile plaice (Pleuronectes platessa L.) in their intertidal and shallow subtidal nursery areas. Vertical position, quantity of energy reserves and fullness of the gut characterized the state of individual fishes. If feeding is visually mediated, the model predicts that, by night, plaice should move to areas of low predation risk and become inactive, whereas by day, plaice should migrate to feed in areas of high prey encounter rate. Vertical zones adopted by day and night and, hence, patterns of migration, should depend on the distributions of predators and prey. When prey are more abundant in the intertidal zone, plaice should move onshore to feed as the tide rises and when prey are more abundant offshore, plaice should move offshore to feed by day. If predators are equally abundant in all zones, the fish should behave as if no predators were present, having no effective refuge. An increase in the abundance of predators with depth results in the restriction of plaice activities to shallower vertical zones, depending on the magnitude of the predation threat. Zones adopted thus depend on the trade-off between energy intake and predation risk. Concordance between predicted behaviour and observed patterns is evident in contrasting habitats. Migration and feeding in the Wadden Sea, where prey are more abundant on intertidal flats, is dominated by the tidal component, whereas on impoverished exposed beaches of the west coast of Scotland, the diurnal component is dominant. Tidally related behaviour persists in the latter environment, not predicted by the model and may be a consequence of using endogenous rhythms to approach optimal behavioural patterns.     

Ghrelin regulates phasic dopamine and nucleus accumbens signaling evoked by food‐predictive stimuli

Environmental stimuli that signal food availability hold powerful sway over motivated behavior and promote feeding, in part, by activating the mesolimbic system. These food‐predictive cues evoke brief (phasic) changes in nucleus accumbens (NAc) dopamine concentration and in the activity of individual NAc neurons. Phasic fluctuations in mesolimbic signaling have been directly linked to goal‐directed behaviors, including behaviors elicited by food‐predictive cues. Food‐seeking behavior is also strongly influenced by physiological state (i.e., hunger vs. satiety). Ghrelin, a stomach hormone that crosses the blood‐brain barrier, is linked to the perception of hunger and drives food intake, including intake potentiated by environmental cues. Notwithstanding, whether ghrelin regulates phasic mesolimbic signaling evoked by food‐predictive stimuli is unknown. Here, rats underwent Pavlovian conditioning in which one cue predicted the delivery of rewarding food (CS+) and a second cue predicted nothing (CS?). After training, we measured the effect of ghrelin infused into the lateral ventricle (LV) on sub‐second fluctuations in NAc dopamine using fast‐scan cyclic voltammetry and individual NAc neuron activity using in vivo electrophysiology in separate groups of rats. LV ghrelin augmented both phasic dopamine and phasic increases in the activity of NAc neurons evoked by the CS+. Importantly, ghrelin did not affect the dopamine nor NAc neuron response to the CS?, suggesting that ghrelin selectively modulated mesolimbic signaling evoked by motivationally significant stimuli. These data demonstrate that ghrelin, a hunger signal linked to physiological state, can regulate cue‐evoked mesolimbic signals that underlie food‐directed behaviors.

     

Biology of Ixodes (Pholeoixodes) hexagonus under laboratory conditions Part II. Effect of mating on feeding and fecundity of females

The effect of mating on the feeding and fecundity ofIxodes (Pholeoixodes) hexagonus females was studied under controlled laboratory conditions of 22–23°C and 98% relative humidity. The feeding period of mated females was 6–15 days and 11–13 days for unmated females. The mean weight of the engorged mated females was 114.84±45.89 mg, whereas, that of the engorged unmated females was significantly lower (80.61±28.84 mg). During the initial slow feeding period, the weight of mated females increased 6.6 times. At the end of the blood feeding, they had increased their initial weight 35.5 times. Unmated females never entered the rapid engorgement phase and up to 12 days of feeding period their mean weight did not increase more than 9.2 times. The pre-oviposition periods of mated and unmated females were 6–15 days and 4–12 days, respectively. The mean of the egg production efficiency was 40.26±12.47% for mated females and 35.68±12.2% for unmated females. The mean of the mass conversion efficiency was 73.6±13.7% for mated females and 66.48 ±16.55% for unmated females. Sixty per cent of the eggs deposited by mated females hatched whereas only 1% of the eggs deposited by unmated females hatched. These results indicate thatI. hexagonus females possess some predisposition for parthenogenesis and only fertility and not fecundity depends on mating.     

Analysis of Mineral Segregation in Euzonus mucronata Burrow Structures: One Possible Method Used in the Construction of Ancient Macaronichnus segregates

Mineralogical segregation of sand grains distinguishes the trace fossil Macaronichnus segregatis, which is composed of a felsic burrow infill with a mafic-and mica-rich burrow mantle. This study focuses on determining the mechanism by which M. segregatis trace-makers segregated mineral grains during deposit feeding. A modern opheliid polychaete, Euzonus mucronata, from Pachena Bay, Vancouver Island (Canada), was examined to explain the activities of their ancient counterparts. Microscopic videotaping of deposit feeding allowed for collection of data on ingestion and excretion through visual grain counts of felsic, mafic, and shell components. Normalization of these grain counts to the composition of the host sediment illustrates preferential ingestion of felsic grains over mafic. Shell fragments were generally avoided and visually mantled the burrows, obscuring the paucity of mafic grains in burrow infills. The avoidance of shell fragments is potentially a function of the large grain size, angular shape, surface texture, and/or associated low nutritive value. The preferential ingestion of felsic grains is attributed to en masse feeding in felsic-rich locales identified through sediment probing. This form of mineral segregation likely reflects the specific nature of the sediment and worm population. Accordingly, en mass deposit feeding in selected felsic-rich localities is one possible mechanism used in the construction of Macaronichnus segregatis and M. segregatis-like structures.     

Antifeedant and toxic effects of drimanes on Colorado potato beetle larvae

Among the drimane compounds tested, the dialdehydes polygodial and warburganal were the most active as antifeedants against Colorado potato beetle larvae, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), in a dual-choice assay with potato, Solanum tuberosum L., leaf discs. Lactones were less effective. Direct observations showed that decreased feeding on leaf discs treated with polygodial and warburganal was accompanied by increased locomotry activity. Topical application of these two compounds on the insect's cuticle decreased food intake of untreated leaf discs, indicating that besides deterrent effects, toxic properties of these molecules influence feeding behaviour.     

浙江分水江水库大型底栖动物群落结构及水质评价

2008年11月-2009年10月,在浙江桐庐分水江水库设置7个站点对大型底栖动物进行逐月调查.结果表明:调查共采集到37种底栖动物,主要由寡毛纲和摇蚊科物种组成.春、夏、秋季优势种均为霍甫水丝蚓,冬季优势种为羽摇蚊.直接收集者在物种数量、密度和生物量上均占绝对优势.群落年均密度和年均生物量分别为(488.0±48.8) ind·m-2和(1.86±0.49) g·m-2.底栖动物密度在站点间无明显差异但存在显著的季节变化,呈现春季＞夏季＞冬季＞秋季的趋势,生物量在站点、季节间均无显著差异.水温和水深是影响底栖动物时空分布的主要因子.Shannon多样性指数和Goodnight-Whitley指数不适合用于该水库的水质评价,其他指数综合显示分水江水库属于轻度污染.     

Differential Impacts of Copepods and Cladocerans on Lake Seston,and Resulting Effects on Zooplankton Growth

In an enclosure study in Schöhsee, a small mesotrophic lake in Northern Germany, the impact of copepods and daphniids on the seston community was studied. In general, these two guilds differ in their feeding behaviour. Copepods actively select their food, with a preference for larger particles, whereas most cladocerans are unselective filter-feeders. In this study we investigate how the impact of the two different grazers affects zooplankton growth. We combine results obtained in the laboratory with results measured in situ in the enclosures. Copepods and cladocerans were cultured on seston from enclosures that were inhabited by density gradients of copepods or daphniids. We observed that Daphnia grew faster on seston that was pre-handled by copepods than on seston that was pre-handled by daphniids, and that somatic growth decreased with increasing densities of daphniids in the enclosures. In contrast, we observed no differences in development rates for copepods grown on the different media. The population growth rates of Daphnia in the Daphnia treatments were determined in the enclosures. Growth differences in both somatic- and population growth of Daphnia were correlated to food quality aspects of the seston. In the laboratory we found that Daphnia growth was correlated with several fatty acids. The strongest regression was with the concentration of 20:43 (r ²= 0.37). This particular fatty acid also showed the highest correlation with growth after normalisation of the fatty acids to the carbon content of the enclosures (r ²= 0.33). On the other hand, in the enclosure the population growth correlated most to the particulate nitrogen content (r ²= 0.78) and only to the N:C ratio, when normalised to carbon (r ²= 0.51).