Changes in species richness and spatial distribution of mosquitoes (Diptera: Culicidae) inferred from museum specimen records and a recent inventory: a case study from Belgium suggests recent expanded distribution of arbovirus and malaria vectors.

Mosquito (Diptera: Culicidae) distribution data from a recent inventory of native and invading mosquito species in Belgium were compared with historical data from the period 1900-1960 that were retrieved from a revision of the Belgian Culicidae collection at the Royal Belgian Institute of Natural Sciences. Both data sets were used to investigate trends in mosquito species richness in several regions in Belgium. The relative change in distribution area of mosquito species was particularly important for species that use waste waters and used tires as larval habitats and species that recently shifted their larval habitat to artificial larval habitats. More importantly, several of these species are known as vectors of arboviruses and Plasmodium sp. and the apparent habitat shift of some of them brought these species in proximity to humans. Similar studies comparing current mosquito richness with former distribution data retrieved from voucher specimens from collections is therefore encouraged because they can generate important information concerning health risk assessment at both regional and national scale.

Nationwide inventory of mosquito biodiversity (Diptera: Culicidae) in Belgium, Europe.

To advance our restricted knowledge on mosquito biodiversity and distribution in Belgium, a national inventory started in 2007 (MODIRISK) based on a random selection of 936 collection points in three main environmental types: urban, rural and natural areas. Additionally, 64 sites were selected because of the risk of importing a vector or pathogen in these sites. Each site was sampled once between May and October 2007 and once in 2008 using Mosquito Magnet Liberty Plus traps. Diversity in pre-defined habitat types was calculated using three indices. The association between species and environmental types was assessed using a correspondence analysis. Twenty-three mosquito species belonging to traditionally recognized genera were found, including 21 indigenous and two exotic species. Highest species diversity (Simpson 0.765) and species richness (20 species) was observed in natural areas, although urban sites scored also well (Simpson 0.476, 16 species). Four clusters could be distinguished based on the correspondence analysis. The first one is related to human modified landscapes (such as urban, rural and industrial sites). A second is composed of species not associated with a specific habitat type, including the now widely distributed Anopheles plumbeus. A third group includes species commonly found in restored natural or bird migration areas, and a fourth cluster is composed of forest species. Outcomes of this study demonstrate the effectiveness of the designed sampling scheme and support the choice of the trap type. Obtained results of this first country-wide inventory of the Culicidae in Belgium may serve as a basis for risk assessment of emerging mosquito-borne diseases.

Human-induced expanded distribution of Anopheles plumbeus, experimental vector of West Nile virus and a potential vector of human malaria in Belgium.

For the majority of native species, human-created habitats provide a hostile environment that prevents their colonization. However, if the conditions encountered in this novel environment are part of the fundamental niche of a particular species, these low competitive environments may allow strong population expansion of even rare and stenotopic species. If these species are potentially harmful to humans, such anthropogenic habitat alterations may impose strong risks for human health. Here, we report on a recent and severe outbreak of the viciously biting and day-active mosquito Anopheles plumbeus Stephens, 1828, that is caused by a habitat shift toward human-created habitats. Although historic data indicate that the species was previously reported to be rare in Belgium and confined to natural forest habitats, more recent data indicate a strong population expansion all over Belgium and severe nuisance at a local scale. We show that these outbreaks can be explained by a recent larval habitat shift of this species from tree-holes in forests to large manure collecting pits of abandoned and uncleaned pig stables. Further surveys of the colonization and detection of other potential larval breeding places of this mosquito in this artificial environment are of particular importance for human health because the species is known as a experimental vector of West Nile virus and a potential vector of human malaria.

Chemical composition and acaricidal properties of Deverra scoparia essential oil (Araliales: Apiaceae) and blends of its major constituents against Tetranychus urticae (Acari: Tetranychidae).

The essential oil of Deverra scoparia Coss. & Durieu was investigated for its acaricidal activity against the worldwide pest twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). The essential oil was analyzed by fast gas chromatography (GC) and GC-mass spectrometry. The activities of its individual and blended constituents were determined. Our study showed that female mortality increased with increasing D. scoparia oil concentrations, with LD50 and LD90 values at 1.79 and 3.2 mg liter(-1), respectively. A reduction in fecundity had already been observed for concentrations of 0.064, 0.08, and 0.26 mg liter(-1) D. scoparia essential oil. Ten major components, comprising 98.52% of the total weight, were identified; a-pinene was the most abundant constituent (31.95%) followed by sabinene (17.24%) and delta3-carene (16.85%). The 10 major constituents of D. scoparia oil were individually tested against T. urticae females. The most potent toxicity was found with alpha-pinene, delta3-carene, and terpinen-4-ol. The presence of all constituents together in the artificial mixture caused a significant decrease in the number of eggs laid by females, at 0.26 mg liter(-1) (11 eggs), compared with the control (50 eggs). The toxicity of blends of selected constituents indicated that the presence of all constituents was necessary to reproduce the toxicity level of the natural oil.

Gamma radiation consequences on desert locust Schistocerca gregaria (Forsk.) digestive system.

Schistocera gregaria (Forsk.) (Orthoptera, Acrididae) remains a major insect pest in Africa, more particularly in the Sahelian zone. Present control methods are only partially efficient. In a previous study, we tested the potentiality of a sterile insect technique (SIT). Males of S. gregaria appeared to be much radiosensitive as already a dose of 3 Gy limited their survival. Gamma-radiations are known to damages the epithelial tissue of midgut, which affects the alimentation in insects. In this work, we show how digestive system of S. gregaria males is affected when submitted to a dose of 4 gamma rays. Nutrition is affected as males stop feeding soon after irradiation and progressively lose weight. Histological analyses on the midgut showed important epithelium damages. The regenerative cells by which the epithelial cells are replaced were damaged on the first days following irradiation. Consequently, regenerative cells are unable to divide and replace the normal loss of midgut cell. After nine days, the entire midgut epithelium was destroyed and only longitudinal muscles layer remained intact. This indicates that low radiation doses should be used if SIT will be applied.

Trans-generational effects on diapause and life-history-traits of an aphid parasitoid.

Transgenerational effects act on a wide range of insects' life-history traits and can be involved in the control of developmental plasticity, such as diapause expression. Decrease in or total loss of winter diapause expression recently observed in some species could arise from inhibiting maternal effects. In this study, we explored transgenerational effects on diapause expression and traits in one commercial and one Canadian field strain of the aphid parasitoid Aphidius ervi. These strains were reared under short photoperiod (8:16 h LD) and low temperature (14 °C) conditions over two generations. Diapause levels, developmental times, physiological and morphological traits were measured. Diapause levels increased after one generation in the Canadian field but not in the commercial strain. For both strains, the second generation took longer to develop than the first one. Tibia length and wing surface decreased over generations while fat content increased. A crossed-generations experiment focusing on the industrial parasitoid strain showed that offspring from mothers reared at 14 °C took longer to develop, were heavier, taller with wider wings and with more fat reserves than those from mothers reared at 20 °C (8:16 h LD). No effect of the mother rearing conditions was shown on diapause expression. Additionally to direct plasticity of the offspring, results suggest transgenerational plasticity effects on diapause expression, development time, and on the values of life-history traits. We demonstrated that populations showing low diapause levels may recover higher levels through transgenerational plasticity in response to diapause-induction cues, provided that environmental conditions are reaching the induction-thresholds specific to each population. Transgenerational plasticity is thus important to consider when evaluating how insects adapt to changing environments.

Male reproductive potential of Aphidius colemani (Hymenoptera: Aphidiinae) exposed to constant or fluctuating thermal regimens.

Prolonged exposure to low temperature generally induces deleterious effects on survival and reproduction of insects. Reproduction costs are well documented in cold-exposed female parasitoids, but there is little information concerning males. In some species, low temperature is suspected to cause male sterility. Mummies of the aphid parasitoid Aphidius colemani Viereck (Hymenoptera: Aphidiinae) were exposed to either fluctuating thermal regimens (FTR: 4 degrees C, 22 h; 20 degrees C, 2 h) or constant low temperature (CLT: 4 degrees C) for 15 d. We verified whether cold exposure can sterilize males and evaluated treatment-related survival, reproductive potential, and mobility parameters. Sterility trials showed that cold-exposed males were all fertile. Survival and reproductive potential of males (e.g., mating success, premating period, and competition for mating) were negatively affected when individuals were exposed to CLT. These alterations were associated with a reduction in locomotion performances during premating period. When parasitoids were exposed to FTR, survival, reproductive potential, and mobility parameters were unaffected. The reduced survival and mobility under CLT, probably results physiological perturbations: processes that may have a limited impact on individuals exposed to FTR. The consequence of mobility reduction on partner acceptance and competitive mating ability is discussed.

Male flowers of Aconitum compensate for toxic pollen with increased floral signals and rewards for pollinators.

Many plants require animal pollinators for successful reproduction; these plants provide pollinator resources in pollen and nectar (rewards) and attract pollinators by specific cues (signals). In a seeming contradiction, some plants produce toxins such as alkaloids in their pollen and nectar, protecting their resources from ineffective pollinators. We investigated signals and rewards in the toxic, protandrous bee-pollinated plant Aconitum napellus, hypothesizing that male-phase flower reproductive success is pollinator-limited, which should favour higher levels of signals (odours) and rewards (nectar and pollen) compared with female-phase flowers. Furthermore, we expected insect visitors to forage only for nectar, due to the toxicity of pollen. We demonstrated that male-phase flowers emitted more volatile molecules and produced higher volumes of nectar than female-phase flowers. Alkaloids in pollen functioned as chemical defences, and were more diverse and more concentrated compared to the alkaloids in nectar. Visitors actively collected little pollen for larval food but consumed more of the less-toxic nectar. Toxic pollen remaining on the bee bodies promoted pollen transfer efficiency, facilitating pollination.

Potential and realized feeding niches of neotropical hispine beetles (Chrysomelidae: Cassidinae, Cephaloleiini).

Accurate descriptions of feeding habits are essential to understanding the evolution of dietary preferences and the high levels of diversification within the Chrysomelidae. Both primary observations and summaries suggest that the cassidine beetle tribe, Cephaloleiini, is a species-rich group of feeding specialists on monocot hosts. However, accurate host ranges are poorly defined for most hispine beetle species. To better document occurrence and feeding, we censused the Cephaloleiini associated with rolled leaves of five species of Marantaceae and six species of Heliconiaceae (Zingiberales) in lowland Central Panama. Additionally, we conducted choice and no-choice feeding tests on a subset of both the plants and beetles encountered in the censuses. Both types of data suggest that most species of Cephaloleiini feed on a greater variety of related plant species than has previously been reported.

Consequences of acclimation on survival and reproductive capacities of cold-stored mummies of Aphidius rhopalosiphi (Hymenoptera: Aphidiinae).

The cold storage of parasitoid mummies is a crucial point during mass production of parasitoids for aphid control in wheat, Triticum spp. In this study, the effect of acclimation to cold before storage of mummies containing Aphidius rhopalosiphi DeStefani-Peres (Hymenoptera: Braconidae: Aphidiinae) was evaluated on survival, sterility, and fecundity of parasitoids. Groups of 1-d-old and 3-d-old mummies were stored at -5 degrees C for 10 d without acclimation or after one of five different acclimation treatments. One-day-old and 3-d-old mummies contain prepupa and postmetamorphosis but not yet sclerotinized adult parasitoids, respectively. The offspring and sex ratio of stored parasitoids were compared with a control that was left at rearing temperatures (20 degrees C). Without acclimation, two-thirds of the parasitoids died during storage, for both ages of mummies tested. For stored 1-d-old mummies, subsequent survival increased under progressive exposure to low temperatures and reached 67.3% after 480 min of acclimation. In the same way, percentage of male sterility decreased with acclimation duration, whereas female fecundity increased. For stored 3-d-old mummies, subsequent survival improved with the duration of the acclimation treatment, but not male sterility and female fecundity.

Potential use of essential oils from Cameroon applied as fumigant or contact insecticides against Sitophilus zeamais Motsch. (Coleoptera: Curculionidae).

Essential oils from seven plants species currently found in Cameroon were extracted by steam distillation and tested for their insecticidal activities against Sitophilus zeamats Motsch. Responses varied with the test applied and the plant species. For the contact toxicity, the acetone was used in order to dilute the pure essential oil. Formulations of 1% of essential oils of Xylopia aethiopica and Ocimum gratissimum were the most toxic and led to 96 and 98% of mortality respectively after 24 h. There was no death in control (0% of mortality). Fumigation test were done by applying 300 microl of pure essential oils in the bottom of closed 800 ml glass containers. In that case, the essential oil of Hyptis spicigera was the most toxic (fumigant) after 48 hours of fumigation followed by Annona seregalensis and Xylopia aethiopica 96 and 95% of mortality respectively. Some of the essential oils of plant species tested are promising for pest control in farmer granaries. However, further investigations are to be done on formulation and side effects.

Variation of DIMBOA and related compounds content in relation to the age and plant organ in maize.

We report the variation of all 1,4-benzoxazin-3-one derivatives content detectable in maize with plant age in roots and aerial parts. Our results show that the concentration of hydroxamic acids, 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one glucoside (DIMBOA-Glc) and its 8-methoxylated analogue (DIM2BOA-Glc) is high after seed germination and then decreases with plant age. Nevertheless, these compounds continue to be biosynthesised during 6-10 days after germination. Variation in concentration of N-O-methylated DIMBOA-Glc (HDMBOA-Glc) is similar to the one of hydroxamic acids in aerial parts. On the contrary, in roots, its concentration remains relatively stable with plant age. After 10 days, HDMBOA-Glc becomes the main compound in roots. This compound is also present in higher concentration than hydroxamic acids in the oldest leaf of 20-day-old maize. The presence of four other DIMBOA related compounds in maize plants depends on variety, age and tissue. The role of these compounds in plant resistance to aphids is discussed.

Are mummy characteristics reliable indicators of diapause and cold tolerance in the parasitoid wasp Aphidius rhopalosiphi (Braconidae, aphidiinae) ?

Many insect species have evolved different overwintering survival strategies such as cold tolerance or diapause. This study investigated the relationship between Aphidius rhopalosiphi mummy colour and cold tolerance and diapause. Mummy colour was insufficient to discriminate diapausing from non-diapausing individuals. This phenotypic character seems to reflect environmental conditions rather than direct developmental time and cocoon thickness (identification criteria of diapause). There is, however, a relationship between cold tolerance and mummy colour. Dark mummies exhibited significantly higher water content, survival at low temperature and lower supercooling point values than pale mummies. Mummy colour in Aphidius rhopalosiphi seems to be a phenotypic indicator of the cold tolerance.

Persistance of the insecticidal activity of five essential oils on the maize weevil Sitophilus zeamais (Motsch.) (Coleoptera: Curculionidae).

Essential oils of aromatic plants are popularise as protectant with low persistance. The evaluation of this duration of activity was carried out for five aromatic plants: Annona senegalensis (Annonaceae), Eucalyptus citriodora et Ecalyptus saligna (Myrtaceae), Lippia rugosa (Verbenaceae) and Ocimum gratissimum (Lamiaceae). They have significant insecticidal activity on S. Zeamais, on the first day of application, this activity decreases after 2 or 4 days. After 8 more than 50% of the efficacy is lossed for all the plants excepted A. senegalensis.

Temperature influences the handling efficiency of an aphid parasitoid through body size-mediated effects.

It is well known that increasing the ambient temperature increases the metabolic rate and consequently, the foraging rate of most insects. However, temperature experienced during the immature stages of insects affects their adult size (an inverse relationship). Because body size is generally correlated to foraging success, we hypothesized that temperature indirectly influences the foraging efficiency of adult insects through developmental effects. We first investigated the role of parasitoid: host body size ratio on the handling time of Aphidius colemani (Viereck) (Hymenoptera: Braconidae), then tested the prediction that increasing temperature during immature development increases the handling time of adults. As expected, parasitoids took longer to handle large aphids than small aphids. However, large parasitoids did not have shorter handling times than small parasitoids except when attacking large (adult) aphids. Developmental temperature had the predicted effect on parasitoids: Individuals reared at 25°C were smaller than those insects reared at 15°C. Parasitoids reared at 15°C had similar short handling times for both first instar and adult aphids, whereas parasitoids reared at 25°C took longer to handle adult aphids than first instar aphids. The size-mediated effect of temperature through development on parasitoid efficiency was opposite to the more familiar direct effect of temperature through metabolic rate. We conclude that the net effect of temperature on foraging insects will depend on its relative influence on immature and adult stages.

Lack of behavioural evidence for kin avoidance in mate choice in a hymenopteran parasitoid (Hymenoptera: Braconidae).

Mechanisms for inbreeding avoidance should be prevalent in insects that reproduce by arrhenotokous haplodiploidy because of the higher potential production of unviable diploid males in inbred matings. Few studies have focused on mating strategies in insect parasitoids and even less on kinship relationships during mate choice. In this study we tested avoidance of kin as mate in the parasitic wasp Aphidius matricariae (Hymenoptera: Braconidae) using an ethological approach. Key mating parameters, such as male wing fanning, latent period before genitalia contact and duration of copulation were measured. No evidence for kin avoidance in mate choice in both A. matricariae males and females was observed in our behaviour (no choice or choice tests) tests. This lack of ethological sib mating avoidance could be due to different factors such as sex determination rule different than the single locus complementary sex determination, making lower the proportion of diploid males in case of sib matings and thus its negative consequence. The existence of other inbreeding avoidance strategies and mechanisms that reduce the probability of 2 receptive relatives meeting in nature may be common, for example, inbred mating may be rare through differential dispersal, delayed maturation, or protandry.

How to visualize the spider mite silk?

Tetranychus urticae (Acari: Tetranychidae) is a phytophagous mite that forms colonies of several thousand individuals. Like spiders, every individual produces abundant silk strands and is able to construct a common web for the entire colony. Despite the importance of this silk for the biology of this worldwide species, only one previous study suggested how to visualize it. To analyze the web structuration, we developed a simple technique to dye T. urticae'silk on both inert and living substrates. Fluorescent brightener 28 (FB) (Sigma F3543) diluted in different solvents at different concentrations regarding the substrate was used to observe single strands of silk. On glass lenses, a 0.5% dimethyl sulfoxide solution was used and on bean leaves, a 0.1% aqueous solution. A difference of silk deposit was observed depending the substrate: rectilinear threads on glass lenses and more sinuous ones on bean leaves. This visualizing technique will help to carry out future studies about the web architecture and silk used by T. urticae. It might also be useful for the study of other silk-spinning arthropods.

Phylogenetic relationships of egg parasitoids (Hymenoptera: Eulophidae) and correlated life history characteristics of their Neotropical Cassidinae hosts (Coleoptera, Chrysomelidae).

Egg parasitoids in the family Eulophidae (Hymenoptera) are an important part of the community of insects attacking neotropical leaf beetles in the subfamily Cassidinae. We present a phylogeny of 24 species of oophagous Eulophidae, using the 28S rDNA, the ITS2 rDNA and the cytochrome b genes, applying the NJ, MP, ML and Bayesian tree reconstruction methods on each data set. We ask whether the phylogenetic relationships of the parasitoids are linked with the life history characteristics of their beetle hosts. We show that cladogenesis in the oophagous Eulophidae does correlate with ovipositional behaviour and, to a lesser extent, diet and tribal affinities of their hosts. Additionally using two methods of simultaneous analysis of several gene sets: the Total Evidence method, and the construction of a "supertree" by Matrix Representation Parsimony (MRP), we substantiate the same major phylogenetic relationships within the Eulophidae.

Effects of 1,4-benzoxazin-3-one derivatives from maize on survival and fecundity of Metopolophium dirhodum (Walker) on artificial diet.

Effects of 2-beta-D-glucopyranosyloxy-4-hydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA-Glc) and DIMBOA-Glc N-O-methylated (HDMBOA-Glc), two compounds present in high concentration in maize, were tested on the aphid Metopolophium dirhodum reared on artificial diet. HDMBOA-Glc and DIMBOA-Glc decrease survival of adults with an LD50 of I mM and 5.6 mM, respectively, after 72 hr of feeding. These compounds also decrease the fecundity of the aphids at concentrations of 2 mM and 1 mM, respectively. At concentrations of 2 mM HDMBOA-Glc and 8 mM DIMBOA-Glc in the diet, the average lifetime fecundity of 10 females is near zero. Offspring mortality on diet with 2 mM DIMBOA-Glc is significantly higher than with the control diet. In contrast, HDMBOA-Glc has no effect on the survival of offspring. The possibility that these compounds protect Poaceae against aphids is discussed.

Overwintering strategies and cold hardiness of two aphid parasitoid species (Hymenoptera: Braconidae: Aphidiinae).

The role of winter diapause in two aphid parasitoid species, Aphidius ervi Haliday and Aphidius rhopalosiphi DeStefani-Peres (Hymenoptera: Braconidae: Aphidiinae), in host synchronization and the induction of cold hardiness was investigated. Parasitoids were reared during three successive generations on Sitobion avenae Fabricius, at 15 degrees C under a photoperiod of 9 h light 15 h dark. Although these conditions are known to be strongly diapause inducing, neither parasitoids showed an incidence of diapause above 65% over the three generations; the rest of the population underwent quiescence. In both parasitoid species, diapausing mummies exhibited greater cold hardiness than non-diapausing mummies, resulting in significantly lower supercooling points (SCP) and in a higher survival rate during long-term exposures at 0 and -10 degrees C. The induction of increased cold hardiness in parasitoids was thus associated with the diapause state. SCPs of third instar larvae of S. avenae were similar to those of non-diapausing mummies of both parasitoid species, but significantly higher than those of diapausing mummies. The effect of winter climate on the stability of the host-parasitoid interaction is discussed.