Carcases and mites

Mites are involved in the decomposition of animal carcases and human corpses at every stage. From initial decay at the fresh stage until dry decomposition at the skeletal stage, a huge diversity of Acari, including members of the Mesostigmata, Prostigmata, Astigmata, Endeostigmata, Oribatida and Ixodida, are an integral part of the constantly changing food webs on, in and beneath the carrion. During the desiccation stage in wave 6 of M,gnin's system, mites can become the dominant fauna on the decomposing body. Under conditions unfavourable for the colonisation of insects, such as concealment, low temperature or mummification, mites might become the most important or even the only arthropods on a dead body. Some mite species will be represented by a few specimens, whereas others might build up in numbers to several million individuals. Astigmata are most prominent in numbers and Mesostigmata in diversity. More than 100 mite species and over 60 mite families were collected from animal carcases, and around 75 species and over 20 families from human corpses.

Effects of a sex-ratio distorting endosymbiont on mtDNA variation in a global insect pest

Background: Patterns of mtDNA variation within a species reflect long-term population structure, but may also be influenced by maternally inherited endosymbionts, such as Wolbachia. These bacteria often alter host reproductive biology and can drive particular mtDNA haplotypes through populations. We investigated the impacts of Wolbachia infection and geography on mtDNA variation in the diamondback moth, a major global pest whose geographic distribution reflects both natural processes and transport via human agricultural activities. Results: The mtDNA phylogeny of 95 individuals sampled from 10 countries on four continents revealed two major clades. One contained only Wolbachia-infected individuals from Malaysia and Kenya, while the other contained only uninfected individuals, from all countries including Malaysia and Kenya. Within the uninfected group was a further clade containing all individuals from Australasia and displaying very limited sequence variation. In contrast, a biparental nuclear gene phylogeny did not have infected and uninfected clades, supporting the notion that maternally-inherited Wolbachia are responsible for the mtDNA pattern. Only about 5% (15/306) of our global sample of individuals was infected with the plutWBI isolate and even within infected local populations, many insects were uninfected. Comparisons of infected and uninfected isofemale lines revealed that plutWBI is associated with sex ratio distortion. Uninfected lines have a 1:1 sex ratio, while infected ones show a 2:1 female bias. Conclusion: The main correlate of mtDNA variation in P. xylostella is presence or absence of the plutWBI infection. This is associated with substantial sex ratio distortion and the underlying mechanisms deserve further study. In contrast, geographic origin is a poor predictor of moth mtDNA sequences, reflecting human activity in moving the insects around the globe. The exception is a clade of Australasian individuals, which may reflect a bottleneck during their recent introduction to this region.

Understanding the alphaviruses: Recent research on important emerging pathogens and progress towards their control

The alphaviruses were amongst the first arboviruses to be isolated, characterized and assigned a taxonomic status. They are globally very widespread, infecting a large variety of terrestrial animals, insects and even fish, and circulate both in the sylvatic and urban/peri-urban environment, causing considerable human morbidity and mortality. Nevertheless, despite their obvious importance as pathogens, there are currently no effective antiviral drugs with which to treat humans or animals infected by any of these viruses. The EU-supported project—VIZIER (Comparative Structural Genomics of Viral Enzymes Involved in Replication, FP6 Project: 2004-511960) was instigated with an ultimate view of contributing to the development of antiviral therapies for RNA viruses, including the alphaviruses [Coutard, B., Gorbalenya, A.E., Snijder, E.J., Leontovich, A.M., Poupon, A., De Lamballerie, X., Charrel, R., Gould, E.A., Gunther, S., Norder, H., Klempa, B., Bourhy, H., Rohayemj, J., L’hermite, E., Nordlund, P., Stuart, D.I., Owens, R.J., Grimes, J.M., Tuckerm, P.A., Bolognesi, M., Mattevi, A., Coll, M., Jones, T.A., Åqvist, J., Unger, T., Hilgenfeld, R., Bricogne, G., Neyts, J., La Colla, P., Puerstinger, G., Gonzalez, J.P., Leroy, E., Cambillau, C., Romette, J.L., Canard, B., 2008. The VIZIER project: preparedness against pathogenic RNA viruses. Antiviral Res. 78, 37–46]. This review highlights some of the major features of alphaviruses that have been investigated during recent years. After describing their classification, epidemiology and evolutionary history and the expanding geographic distribution of Chikungunya virus, we review progress in understanding the structure and function of alphavirus replicative enzymes achieved under the VIZIER programme and the development of new disease control strategies.

The effect of acetylsalicylic acid and oxalic acid on Myzus persicae and Aphidius colemani

Plants can respond to damage by pests with both induced direct defences and indirect defences by the attraction of their natural enemies. Foliar application of several plant-derived chemicals, such as salicylic acid and oxalic acid, can induce these defence mechanisms. The effect of acetylsalicylic acid and oxalic acid on the aphid Myzus persicae Sulzer (Homoptera: Aphididae) and its parasitoid Aphidius colemani Viereck (Hymenoptera: Aphidiidae) was investigated. Experiments were carried out with direct application of acetylsalicylic and oxalic acids on these insects, as well as choice and no-choice tests using foliar application of both chemicals on Brussels sprouts plants, Brassica oleracea var. gemmifera L. (Brassicaceae). Parasitoids were given a choice between treated and untreated plants for oviposition, and the effects of the chemicals on aphid and parasitoid development were determined. Although direct application of both chemicals increased aphid mortality, their foliar application did not induce resistance against aphids. The foliar application of such compounds, even in low concentration as shown in the choice tests, has the potential to induce indirect plant defences against aphids by encouraging aphid parasitisation. Although the direct application of both chemicals reduced parasitoid emergence from their hosts, the foliar application of acetylsalicylic acid and low concentrations of oxalic acid did not have a negative effect on parasitoid emergence ability. However, 10 mm oxalic acid reduced the number of emerged parasitoids in no-choice experiments. This study shows that foliar application of acetylsalicylic and oxalic acids has the potential to encourage aphid parasitisation, but care is needed as high concentrations of oxalic acid can have a negative effect on these beneficial organisms.

Forensic acarology: an introduction

Mites can be found in all imaginable terrestrial habitats, in freshwater, and in salt water. Mites can be found in our houses and furnishings, on our clothes, and even in the pores of our skin-almost every single person carries mites. Most of the time, we are unaware of them because they are small and easily overlooked, and-most of the time-they do not cause trouble. In fact, they may even proof useful, for instance in forensics. The first arthropod scavengers colonising a dead body will be flies with phoretic mites. The flies will complete their life cycle in and around the corpse, while the mites may feed on the immature stages of the flies. The mites will reproduce much faster than their carriers, offering themselves as valuable timeline markers. There are environments where insects are absent or rare or the environmental conditions impede their access to the corpse. Here, mites that are already present and mites that arrive walking, through air currents or material transfer become important. At the end of the ninetieth century, the work of Jean Pierre M,gnin became the starting point of forensic acarology. M,gnin documented his observations in 'La Faune des Cadavres' [The Fauna of Carcasses]. He was the first to list eight distinct waves of arthropods colonising human carcasses. The first wave included flies and mites, the sixth wave was composed of mites exclusively. The scope of forensic acarology goes further than mites as indicators of time of death. Mites are micro-habitat specific and might provide evidential data on movement or relocation of bodies, or locating a suspect at the scene of a crime. Because of their high diversity, wide occurrence, and abundance, mites may be of great value in the analysis of trace evidence.

Megnin re-analysed: the case of the newborn baby girl, Paris, 1878

This paper analyses acarological evidence from a 130-year-old forensic investigation. It was the first case in forensic acarology, i.e., the first case where mites provided substantial information to estimate the post-mortem interval (PMI). In 1878, the mites found in the mummified body of a newborn baby girl in Paris, France, were studied by acarologist and forensic entomologist Jean Pierre M,gnin. M,gnin estimated around 2.4 million mites in the skull and identified them as Tyroglyphus longior (Gervais), a junior synonym of Tyrophagus longior. He suggested that the arrival of these mites at the corpse would have occurred by phoresy on carrier insects, roughly 5 months before the autopsy. There is no doubt about the identification of the mites, M,gnin was a highly respected acarologist. However, two main factors affecting the biology of Tyrophagus mites were not included in the original analysis. First, M,gnin stated that the mites were phoretic. However, he probably did not have access to information about the natural history of the species, because as a rule Tyrophagus mites are non-phoretic. Considering the omnipresence of Tyrophagus mites in soil, most likely the mites will have arrived almost immediately after death. Second, temperature was not taken into account during the estimations of the mite population growth rate. The new analysis is based on current knowledge of Tyrophagus biology and includes temperature, estimated following a handful of weather reports of the years 1877 and 1878. The new projections indicate that non-phoretic mites may have colonised the body just after death and the colony would have built up over 8 months, contrary to the 5 months proposed by M,gnin. This new lapse of time agrees with the PMI proposed by Brouardel: on 15 January 1878 he postulated the death of the newborn to have occurred some 8 months before the autopsy.

Phoretic mites associated with animal and human decomposition

Phoretic mites are likely the most abundant arthropods found on carcases and corpses. They outnumber their scavenger carriers in both number and diversity. Many phoretic mites travel on scavenger insects and are highly specific; they will arrive on a particular species of host and no other. Because of this, they may be useful as trace indicators of their carriers even when their carriers are absent. Phoretic mites can be valuable markers of time. They are usually found in a specialised transitional transport or dispersal stage, often moulting and transforming to adults shortly after arrival on a carcase or corpse. Many are characterised by faster development and generation cycles than their carriers. Humans are normally unaware, but we too carry mites; they are skin mites that are present in our clothes. More than 212 phoretic mite species associated with carcases have been reported in the literature. Among these, mites belonging to the Mesostigmata form the dominant group, represented by 127 species with 25 phoretic mite species belonging to the family Parasitidae and 48 to the Macrochelidae. Most of these mesostigmatids are associated with particular species of flies or carrion beetles, though some are associated with small mammals arriving during the early stages of decomposition. During dry decay, members of the Astigmata are more frequently found; 52 species are phoretic on scavengers, and the majority of these travel on late-arriving scavengers such as hide beetles, skin beetles and moths. Several species of carrion beetles can visit a corpse simultaneously, and each may carry 1-10 species of phoretic mites. An informative diversity of phoretic mites may be found on a decaying carcass at any given time. The composition of the phoretic mite assemblage on a carcass might provide valuable information about the conditions of and time elapsed since death.

Gene flow, risk assessment and the environmental release of transgenic plants

The release of genetically modified plants is governed by regulations that aim to provide an assessment of potential impact on the environment. One of the most important components of this risk assessment is an evaluation of the probability of gene flow. In this review, we provide an overview of the current literature on gene flow from transgenic plants, providing a framework of issues for those considering the release of a transgenic plant into the environment. For some plants gene flow from transgenic crops is well documented, and this information is discussed in detail in this review. Mechanisms of gene flow vary from plant species to plant species and range from the possibility of asexual propagation, short- or long-distance pollen dispersal mediated by insects or wind and seed dispersal. Volunteer populations of transgenic plants may occur where seed is inadvertently spread during harvest or commercial distribution. If there are wild populations related to the transgenic crop then hybridization and eventually introgression in the wild may occur, as it has for herbicide resistant transgenic oilseed rape (Brassica napus). Tools to measure the amount of gene flow, experimental data measuring the distance of pollen dispersal, and experiments measuring hybridization and seed survivability are discussed in this review. The various methods that have been proposed to prevent gene flow from genetically modified plants are also described. The current "transgenic traits'! in the major crops confer resistance to herbicides and certain insects. Such traits could confer a selective advantage (an increase in fitness) in wild plant populations in some circumstances, were gene flow to occur. However, there is ample evidence that gene flow from crops to related wild species occurred before the development of transgenic crops and this should be taken into account in the risk assessment process.

Numerical abundance of invasive ants and monopolisation of exudate-producing resources - a chicken and egg situation

1. Invasive ants commonly reach abnormally high abundances and have severe impacts on the ecosystems they invade. Current invasion theory recognises that not only negative interactions, such as natural enemy release, but positive interactions, such as facilitation, are important in causing this increased abundance. 2. For invasive ants, facilitation can occur through mutualism with exudate-producing plants and insects. To obtain such partnerships, however, invaders must first displace native ants, whose communities are highly structured around such resources. 3. By manipulating the abundance of an invasive ant relative to a native, we show that a minimum threshold abundance exists for invasive ants to monopolise exudate-producing resources. In addition, we show that behavioural dominance is context dependent and varies with spatial location and numerical abundance. 4. Thus, we suggest a 'facilitation-threshold' hypothesis of ant invasion, whereby a minimum abundance of invasive ants is required before facilitation and behavioural dominance can drive abundance rapidly upwards through positive feedback.

Macroevolutionary patterns in the origin of mutualisms involving ants

Ants are a diverse and abundant insect group that form mutualistic associations with a number of different organisms from fungi to insects and plants. Here, we use a phylogenetic approach to identify ecological factors that explain macroevolutionary trends in the mutualism between ants and honeydew-producing Homoptera. We also consider association between ant-Homoptera, ant-fungi and ant-plant mutualisms. Homoptera-tending ants are more likely to be forest dwelling, polygynous, ecologically dominant and arboreal nesting with large colonies of 10(4)-10(5) individuals. Mutualistic ants (including those that garden fungi and inhabit ant-plants) are found in under half of the formicid subfamilies. At the genus level, however, we find a negative association between ant-Homoptera and ant-fungi mutualisms, whereas there is a positive association between ant-Homoptera and ant-plant mutualisms. We suggest that species can only specialize in multiple mutualisms simultaneously when there is no trade-off in requirements from the different partners and no redundancy of rewards.

Environmental variation at the onset of independent foraging affects full-grown body mass in the red fox

The period following the withdrawal of parental care has been highlighted as a key developmental period for juveniles. One reason for this is that juveniles cannot forage as competently as adults, potentially placing them at greater risk from environmentally-induced changes in food availability. However, no study has examined this topic. Using a long-term dataset on red foxes (Vulpes vulpes), we examined (i) dietary changes that occurred in the one-month period following the attainment of nutritional independence, (ii) diet composition in relation to climatic variation, and (iii) the effect of climatic variation on subsequent full-grown mass. Diet at nutritional independence contained increased quantities of easy-to-catch food items (earthworms and insects) when compared with pre-independence. Interannual variation in the volume of rainfall at nutritional independence was positively correlated to the proportion of earthworms in cub diet. Pre-independence cub mass and rainfall immediately following nutritional independence explained a significant proportion of variance in full-grown mass, with environmental variation affecting full-grown mass of the entire cohorts. Thus, weather-mediated availability of easy-to-catch food items at a key developmental stage has lifelong implications for the development of juvenile foxes by affecting full-grown mass, which in turn appears to be an important component of individual reproductive potential.

Diverse mariner-like elements in fig wasps

Mariner transposable elements are widespread and diverse in insects. We screened 10 species of fig wasps (Hymenoptera: Agaonidae) for mariner elements. All 10 species harbour a large diversity of mariner elements, most of which have interrupted reading frames in the transposase gene region, suggesting that they are inactive and ancient. We sequenced two full-length mariner elements and found evidence to suggest that they are inserted in the genome at a conserved region shared by other hymenopteran taxa. The association between mariner elements and fig wasps is old and dominated by vertical transmission, suggesting that these 'selfish genetic elements' have evolved to impart only very low costs to their hosts.

Genotypic and phenotypic diversity of a baculovirus population within an individual insect host

It is becoming increasingly apparent that many pathogen populations, including those of insects, show high levels of genotypic variation. Baculoviruses are known to be highly variable, with isolates collected from the same species in different geographical locations frequently showing genetic variation and differences in their biology. More recent Studies at smaller scales have also shown that virus DNA profiles from individual larvae can show polymorphisms within and between populations of the same species. Here, we investigate the genotypic and phenotypic variation of an insect baculovirus infection within a single insect host. Twenty four genotypically distinct nucleopolyhedrovirus (NPV) variants were isolated from an individual pine beauty moth, Panolis flammea, caterpillar by in vivo cloning techniques. No variant appeared to be dominant in the population. The Pafl NPV variants have been mapped using three restriction endonucleases and shown to contain three hypervariable regions containing insertions of 70-750 bp. Comparison of seven of these variants in an alternative host, Mamestra brassicae, demonstrated that the variants differed significantly in both pathogenicity and speed of kill. The generation and maintenance of pathogen heterogeneity are discussed. (c) 2005 Elsevier Inc. All rights reserved.

Resistance is costly: trade-offs between immunity, fecundity and survival in the pea aphid

Parasitoids are among the most important natural enemies of insects in many environments. Acyrthosiphon pisum, the pea aphid, is a common pest of the leguminous crops in temperate regions. Pea aphids are frequently attacked by a range of endoparasitic wasps, including the common aphidiine, Aphidius ervi. Immunity to parasitoid attack is thought to involve secondary symbiotic bacteria, the presence of which is associated with the death of the parasitoid egg. It has been suggested that there is a fecundity cost of resistance, as individuals carrying the secondary symbionts associated with parasitoid resistance have fewer offspring. Supporting this hypothesis, we find a positive relationship between fecundity and susceptibility to parasitoid attack. There is also a negative relationship between fecundity and off-plant survival time (which positively correlates with resistance to parasitoid attack). Taken together, these results suggest that the aphids can either invest in defence (parasitoid resistance, increased off-plant survival time) or reproduction, and speculate that this may be mediated by changes in the aphids' endosymbiont fauna. Furthermore, there is a positive relationship between aphid size and resistance, suggesting that successful resistance to parasitoid attack may involve physical, as well as physiological, defences.