On the mimetic association between nymphs of Hyalymenus spp. (Hemiptera: Alydidae) and ants

Nymphs of Hyalymenus , unlike adults, have a highly differentiated ant-like morphology. Both H. tarsatus and H. limbativentris feed mainly on reproductive parts of composites and solanaceous plants, respectively. Mimetic nymphs were observed on plants, together with ants, both day and night; adult Hyalymenus , however, are predominantly nocturnal. Ant-resemblance in nymphs is achieved by several structural adaptations which, when coupled with the mimic's zig-zag locomotion and constantly agitated antennae, produces a striking visual deception. Experiments in captivity showed that mimetic nymphs, but not adult Hyalymenus , are somewhat protected against attacks from the praying mantid Oxyopsis media found on their host plant. Colour and size changes through different nymphal instars of Hyalymenus allow the immature bugs to resemble, during their development, differently sized and coloured ant models. Similar-looking ant species seem to act as Mullerian mimics toward insectivorous vertebrates and invertebrates that avoid ants. It is suggested that nymphs of Hyalymenus gain Batesian protection by resembling available ant models of different Mullerian complexes. Density-dependent selection is thought to be responsible for the observed differences in mimetic morph proportions between populations of mimics, as well as for the mimetic strategy itself employed by nymphs of Hyalymenus.     

Differential cold hardiness in adults and nymphs of the peach-potato aphid Myzus persicae

The LT₅₀ (lethal temperature) of first instar and adult stages of the peach-potato aphid Myzus persicae was lowered following long term acclimation at low temperatures.
First instars consistently showed greater cold hardiness than adult stages at each acclimation temperature, with the differential increasing as the temperature was lowered. When maintained at 5°C (the lowest acclimation regime) nymphs and adults had dLT₅₀8.3°C and 4.7°C respectively lower than those for non-acclimated individuals.
When 10°C acclimated adults were returned to 20°C, the acclimation effect was retained in full for 6 days but complete deacclimation occurred by day 10. In contrast the LT₅₀ of their progeny increased gradually from the first day of adult deacclimation towards the level of the unacclimated control over a period of 10 days.
A change in cold hardiness was observed in first instars according to their position in the birth sequence. The LT₅₀ of first-born nymphs (day 1 of reproduction) from 20°C parents was - 15.9°C rising to - 8.3°C by day 4 and remaining at this level until the end of the reproductive period.
The differential mortality between nymphs and adults observed in the laboratory was supported by the results of a field experiment. Adult aphids kept in clip-cages on a crop of oilseed rape showed greater mortality compared with those introduced as nymphs when the minimum temperature fell below -4°C for the first time in winter. At - 10°C mortality of aphids introduced as adults approached 100% whereas more than 50% of those introduced as nymphs were still alive at this temperature.     

Does developmental acclimatization reduce the susceptibility to predation in newt larvae?

Many organisms respond to the heterogeneity of abiotic environmental conditions by plastic modifications of their phenotypes (acclimation or acclimatization). Despite considerable research efforts in this area, the beneficial (adaptive) effect of acclimation or acclimatization is still debated. We examined whether the development of newt larvae (Ichthyosaura alpestris) under different natural light and thermal conditions subsequently altered their susceptibility to predation in sun‐exposed versus shaded tanks in nature. During predation trials in various light and temperature conditions, newt larvae that developed in sun‐exposed warmer tanks consistently suffered from higher predation by dragonfly nymphs (Aeshna cyanea) compared to larvae from shaded or colder tanks. We conclude that higher sun exposure during embryonic and larval development negatively affects antipredator performance even in sun‐exposed tanks: this result is inconsistent with the beneficial acclimation hypothesis. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ●● , ●●–●●.     

Evolution of insect wings and development – new details from Palaeozoic nymphs

The nymphal stages of Palaeozoic insects differ significantly in morphology from those of their modern counterparts. Morphological details for some previously reported species have recently been called into question. Palaeozoic insect nymphs are important, however – their study could provide key insights into the evolution of wings, and complete metamorphosis. Here we review past work on these topics and juvenile insects in the fossil record, and then present both novel and previously described nymphs, documented using new imaging methods. Our results demonstrate that some Carboniferous nymphs – those of Palaeodictyopteroidea – possessed movable wing pads and appear to have been able to perform simple flapping flight. It remains unclear whether this feature is ancestral for Pterygota or an autapomorphy of Palaeodictyopteroidea. Further characters of nymphal development which were probably in the ground pattern of Pterygota can be reconstructed. Wing development was very gradual (archimetaboly). Wing pads did not protrude from the tergum postero‐laterally as in most modern nymphs, but laterally, and had well‐developed venation. The modern orientation of wing pads and the delay of wing development into later developmental stages (condensation) appears to have evolved several times independently within Pterygota: in Ephemeroptera, Odonatoptera, Eumetabola, and probably several times within Polyneoptera. Selective pressure appears to have favoured a more pronounced metamorphosis between the last nymphal and adult stage, ultimately reducing exploitation competition between the two. We caution, however, that the results presented herein remain preliminary, and the reconstructed evolutionary scenario contains gaps and uncertainties. Additional comparative data need to be collected. The present study is thus seen as a starting point for this enterprise.     

Acarologic risk of exposure to Borrelia burgdorferi spirochaetes: long-term evaluations in north-western California, with implications for Lyme borreliosis risk-assessment models

Over a 5-year period (1997-2001) the population densities of Ixodes pacificus Cooley & Kohls (Acari: Ixodidae) nymphs infected with spirochaetes of Borrelia burgdorferi sensu lato (s.l.) were evaluated in areas of 2000 ha at two localities (CHR, nine sites; HREC, seven sites) 25 km apart in Mendocino County, north-western California. The 5-year median density of infected nymphs was significantly higher at CHR than at HREC (0.51 vs. 0.09 per 100 m(2) and site-specific yearly densities exceeding one infected nymph per 100 m2 were 10-fold more likely to occur at CHR than at HREC. The importance of long-term data in acarologic risk assessment was demonstrated by significantly higher median yearly densities of infected nymphs at CHR from 1997 to 1999, whereas both areas had similar densities during 2000-2001. Overall, the causative agent of Lyme borreliosis in North America, B. burgdorferi Johnson et al. sensu stricto (s.s.) accounted for 76% of 46 genetically characterized B. burgdorferi s.l. infections from I. pacificus nymphs. Tremendous variability in acarologic risk was recorded within both areas: yearly densities of infected nymphs varied 11-97-fold between sites at CHR and 8-30-fold at HREC. Part of this variation could be explained by environmental traits, most notably deer usage. However, correlations between environmental factors and density of infected nymphs (for CHR and HREC combined) did not necessarily apply when these areas were considered separately. Thus, a Lyme borreliosis ecology model developed in one of these areas needs testing in the other area.     

中华真地鳖低龄若虫消化道结构及取食习性

解剖喂食不同饲料中华真地鳖EupolyphagasinensisWalker的低龄若虫 ,结果表明 ,低龄若虫消化道与成虫消化道结构相同 ,具有胃盲囊和马氏管 ;嗉囊、中肠和后肠分别占消化道总长的比率与中龄若虫相同 ,具有消化食物的能力。观察消化道各部分的滞留物变化情况 ,发现 1龄若虫取食了饲养土中的腐殖质和配合饲料 ,表明孵化后的若虫需要喂食以满足营养需要。     

Drift dispersal of mayfly nymphs in the presence of chemical and visual cues from diurnal drift- and nocturnal benthic-foraging fishes

1. The drift of Baetis thermicus nymphs in the presence of chemical, visual and hydrodynamic cues, considered individually and in combination, produced by different predatory fishes was examined experimentally in laboratory streams. Masu salmon ( Oncorhynchus masou ) and freshwater sculpin ( Cottus nozawae ) are typical drift- and benthic-foraging fishes, respectively.
2. Observations of fish swimming in the streams revealed differing diel periodicity between the species; sculpin were nocturnal foragers and salmon diurnal.
3. The drift rate of Baetis by night increased in the presence of chemical cues from sculpin, with other cues having no interactive effects. In contrast, the drift rate increased primarily in the presence of both chemical and, particularly, visual cues from salmon, although no additional effects were found for any non-visual cues. Visual cues could enable Baetis to assess precisely the predation risk from foraging salmon by day, whereas Baetis could not use visual cues to detect sculpin either at night, because of the low light intensity, or during the day, because of the low activity of sculpin at that time.
4. In natural streams, which are often inhabited by several predatory fish employing different modes of foraging, invertebrates may be able to precisely assess the risk and effectively to avoid predators by using cues unique to each.     

Nocturnal drift of mayfly nymphs as a post-contact antipredator mechanism

1. The predominantly nocturnal constrained drift of stream invertebrates is commonly regarded as a behaviour that avoids encounters with visually foraging fish in the water column. The alternative explanation, that drift peaks are caused by bottom-feeding, nocturnal predators, has rarely been tested.
2. We examined these hypotheses by collecting invertebrate drift in five streams in northern Finland: one with brown trout ( Salmo trutta , a drift-feeding fish), one with alpine bullhead ( Cottus poecilopus , a benthic fish), one with both species, and two fishless streams.
3. Drift by Baetis mayflies was aperiodic or slightly diurnal in both fishless streams on all sampling occasions. In contrast, drift was nocturnal in streams with trout and, to a lesser extent, in the stream with bullhead. Non-dipteran prey drifted mainly nocturnally in all streams with fish, whereas Diptera larvae were less responsive to the presence of fish.
4. In laboratory experiments, bullheads were night-active, causing a much higher frequency of drift by touching Baetis at night than during the day. Thus, increased nocturnal drift may serve to avoid both visual predators (a pre-contact response) and benthic fish (a post-contact response). In streams with bottom-feeding fish, nocturnal drift should be caused by increased drift by night rather than by reduced drift by day.     

Regeneration in the auditory system of nymphal and adult bush crickets Tettigonia viridissima

Regeneration and reestablishment of synaptic connections is an important topic in neurobiological research. In the present study, the regeneration of auditory afferents and the accompanying effects in the central nervous system are investigated in nymphs and adults of the bush cricket Tettigonia viridissima L. (Orthoptera: Tettigoniidae). In all animals in which the tympanal nerve is crushed, neuronal tracing shows a regrowth of the afferents into the prothoracic ganglion. This regeneration is seen in both adult and nymphal stages and starts 10–15 days after nerve crushing. Physiological recordings from the leg nerve indicate a recovery of tympanal fibres and a formation of functional connections to interneurones in the same time range. Electrophysiological recordings from the neck connective suggest additional contralateral sprouting of interneurones and the formation of aberrant connections. The regeneration processes of the tympanal nerve in nymphal stages and adults appear to be similar.