Yves Brostaux

Microorganisms from aphid honeydew attract and enhance the efficacy of natural enemies

Aphids are one of the most serious pests of crops worldwide, causing major yield and economic losses. To control aphids, natural enemies could be an option but their efficacy is sometimes limited by their dispersal in natural environment. Here we report the first isolation of a bacterium from the pea aphid Acyrthosiphon pisum honeydew, Staphylococcus sciuri, which acts as a kairomone enhancing the efficiency of aphid natural enemies. Our findings represent the first case of a host-associated bacterium driving prey location and ovipositional preference for the natural enemy. We show that this bacterium has a key role in tritrophic interactions because it is the direct source of volatiles used to locate prey. Some specific semiochemicals produced by S. sciuri were also identified as significant attractants and ovipositional stimulants. The use of this host-associated bacterium could certainly provide a novel approach to control aphids in field and greenhouse systems.

Carrion Beetles Visiting Pig Carcasses during Early Spring in Urban, Forest and Agricultural Biotopes of Western Europe

Abstract Carrion beetles are important in terrestrial ecosystems, consuming dead mammals and promoting the recycling of organic matter into ecosystems. Most forensic studies are focused on succession of Diptera while neglecting Coleoptera. So far, little information is available on carrion beetles postmortem colonization and decomposition process in temperate biogeoclimatic countries. These beetles are however part of the entomofaunal colonization of a dead body. Forensic entomologists need databases concerning the distribution, ecology and phenology of necrophagous insects, including silphids. Forensic entomology uses pig carcasses to surrogate human decomposition and to investigate entomofaunal succession. However, few studies have been conducted in Europe on large carcasses. The work reported here monitored the presence of the carrion beetles (Coleoptera: Silphidae) on decaying pig carcasses in three selected biotopes (forest, crop field, urban site) at the beginning of spring. Seven species of Silphidae were recorded: Nicrophorus humator (Gleditsch), Nicrophorus vespillo (L.), Nicrophorus vespilloides (Herbst), Necrodes littoralis L., Oiceoptoma thoracica L., Thanatophilus sinuatus (Fabricius), Thanatophilus rugosus (L.). All of these species were caught in the forest biotope, and all but O. thoracica were caught in the agricultural biotope. No silphids were caught in the urban site.

Propensity of the Tomato Leafminer, Tuta absoluta (Lepidoptera: Gelechiidae), to Develop on Four Potato Plant Varieties

The tomato leafminer, Tuta absoluta (Lepidoptera: Gelechiidae), is now considered to be one of the most damaging invasive pests of tomatoes in the world. Tomato is regarded as the main host of T. absoluta, but the pest can also feed, develop and reproduce on other cultivated Solanaceae, such as potato (Solanum tuberosum L). In the present study, we examined the ability of T. absoluta to develop on four commonly cultivated varieties of potato, under laboratory conditions. The survival rate of T. absoluta did not differ between the five tested host plants (tomato: Solanum lycopersicum cv. Moneymaker; and potato: Solanum tuberosum cv. Spunta, Charlotte, Nicola, and Bintje), but its development time (egg to pupation) was significantly affected. Compared to tomato, development times were longer on Bintje and shorter on Nicola, Charlotte, and Spunta. These results show the high capacity of T. absoluta to develop on potato crops.ResumenEl minador de la hoja en tomate, Tuta absoluta (Lepidoptera: Gelechiidae), está considerado actualmente como una de las plagas invasivas de mayor daño en tomates en el mundo. Se considera al tomate como el hospedante principal de T. absoluta, pero la plaga también se puede alimentar, desarrollar y reproducir en otras Solanáceas cultivadas, como la papa (Solanum tuberosum L.). En el presente estudio examinamos la habilidad de T. absoluta para desarrollarse en cuatro variedades de papa cultivadas comunmente, bajo condiciones de laboratorio. El nivel de sobrevivencia de T. absoluta no difirió entre los cinco hospedantes probados (tomate: Solanum lycopersicum cv. Moneymaker; y papa: Solanum tuberosum cv. Spunta, Charlotte, Nicola, y Bintje), pero su tiempo de desarrollo (de huevo hasta pupa) se afectó significativamente. En comparación con el tomate, los tiempos de desarrollo fueron más largos en Bintje y más cortos en Nicola, Charlotte, y Spunta. Estos resultados muestran la alta capacidad de T. absoluta para desarrollarse en cultivos de papa.

Increased fecundity of malathion-specific resistant beetles in absence of insecticide pressure

Despite that resistance frequency is assumed to decline when selective pressure is relaxed, the stability of resistance frequency has been observed in some insects in the absence of insecticide. In the red flour beetle, Tribolium castaneum, the first case of malathion-resistance was reported in the early 1960s. The malathion-specific resistant phenotype has now almost completely replaced the susceptible one in red flour beetle populations. In the present study, several life-history traits that could influence the fitness of the insects were compared between insecticide-susceptible and malathion-specific resistant populations of the red flour beetle. On average, egg fertility and egg-to-adult development time did not differ between susceptible and resistant populations. However, the fecundity of resistant females was greater than that of susceptible ones. Generally, differences in development time between insecticide resistant and susceptible populations are considered as having more effect on fitness than do differences in fecundity. However, the observed increased female fecundity may participate, in combination with the previously observed increased male reproductive success, to the development and the stability of malathion-specific resistance in T. castaneum.

Honey bee colony losses in Belgium during the 2008–9 winter

(2010). Honey bee colony losses in Belgium during the 2008–9 winter. Journal of Apicultural Research: Vol. 49, No. 4, pp. 337-339.

Role of long-chain hydrocarbons in the aggregation behaviour of Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae)

The multicoloured Asian ladybirds, Harmonia axyridis (Pallas), form large aggregations inside dwellings to survive cold winters, causing annoyance to householders due to their abundance, allergenic properties and problems consequent on reflex bleeding. Flight to overwintering sites and macrosite choice of this species is well documented. H. axyridis shows a hypsotactic behaviour and a clear preference for contrasting visual elements. However, how the microsite is selected remains undocumented, although a better understanding of the factors implicated could lead to the development of new control methods for this pest. In this work, we hypothesised that non-volatile compounds are involved in the microsite choice and aggregation of this beetle. Long chain hydrocarbons were identified at aggregation sites, comprising saturated and unsaturated homologues. An aggregation bioassay was then conducted on overwintering individuals, highlighting the retention capacity of the identified compounds on the tested ladybirds. Additional investigations showed that H. axyridis males and females, originating from overwintering sites, deposit a similar blend of molecules while walking. A Y-shaped tube assay revealed that this blend is used by male and female congeners as cue allowing individuals to orientate towards the treated side of the olfactometer. These results suggest the use of two different blends of long chain hydrocarbons by H. axyridis during its aggregative period, the first one to lead conspecifics towards aggregation sites (microsites) and the second to ensure the cohesion of the aggregation. These findings support the potential use of these blends, in association with volatiles, in the design of traps in order to control infestations of this species in dwellings.

Honeydew volatile emission acts as a kairomonal message for the Asian lady beetle Harmonia axyridis (Coleoptera: Coccinellidae).

Abstract  The Asian lady beetle Harmonia axyridis Pallas is considered as an invasive species in most territories where it has been introduced. Because aphid honeydew acts as an attractant for many aphid predators and parasitoids, the objectives of this work were to collect and identify the volatile compounds released from the aphid excretory product to evaluate how these semiochemicals could affect the H. axyridis foraging behavior. Twelve volatile chemicals were identified from the Megoura viciae Buckton honeydew including four alcohols, three ketones, three aldehydes, a pyrazine and a monoterpene. The volatiles 3‐methyl‐1‐butanol and 3‐methyl‐butanal were highlighted as the two most abundant semiochemicals released from the M. viciae honeydew. Vicia faba L. plants treated with crude honeydew attracted more than 80% of the tested individuals with 40% of attracted beetles located on the plant. Four volatile compounds (3‐hydroxy‐2‐butanone, 3‐methyl‐butanal, 3‐methyl‐1‐butanol and limonene) were also highlighted to attract more than 75% of the coccinellids toward the odor source and to locate about 35% of them on the plants. Limonene was the most efficient attractant since 89% of the H. axyridis responded to this odor. The use of the identified semiochemicals as well as the composition of an artificial honeydew could certainly be helpful to control the dispersal of the Asian lady beetle H. axyridis.

Inter-laboratory evaluation of a duplex RT-PCR method using crude extracts for the simultaneous detection of Prune dwarf virus and Prunus necrotic ringspot virus

The operational capacity of a duplex RT-PCR method for simultaneous detection of Prune dwarf virus (PDV) and Prunus necrotic ringspot virus (PNRSV) has been established by nine European laboratories. A total of 576 samples from Prunus trees with known sanitary status, corresponding to 32 samples in two repetitions for each laboratory, were analysed. The level of sensitivity achieved by the method was 98.3% for PDV and 90.4% for PNRSV. The specificity was 87.4% for PDV and 94.3% for PNRSV. The unilateral 95% confidence intervals were calculated for all these values. Cohen’s Kappa coefficient of repeatability and reproducibility of the technique indicated a strong agreement between data. Likelihood ratios were 7.50 (positive) and 0.02 (negative) for PDV. For PNRSV, the positive likelihood ratio was 15.00 while the negative likelihood ratio was 0.11. In addition, post-test probabilities of infection were calculated to manage the risk associated with the routine use of this method. This allows an accurate test result interpretation to facilitate the integration of this new technique into a certification scheme.

Phenological patterns in a natural population of a tropical timber tree species, Milicia excelsa (Moraceae): evidence of Isolation By Time and its interaction with feeding strategies of dispersers

PREMISE OF THE STUDY Population genetic structuring over limited timescales is commonly viewed as a consequence of spatial constraints. Indirect approaches have recently revealed reproductive isolation resulting from flowering time (so-called isolation by time, IBT). Since phenological processes can be subject to selection, the persistence of flowering asynchrony may be due to opposing selective pressures during mating, dispersal, and regeneration phases. Our study aimed to investigate phenology, fruit handling by animals, and their interaction in a timber tree species, Milicia excelsa. METHODS We analyzed phenological data collected over 6 years on 69 genotyped trees in a Cameroonian natural rainforest complemented by data from germination trials and field observations of dispersers. KEY RESULTS Initiation of flowering was correlated with variation in temperature and relative humidity, but was also affected by genetic factors: pairwise differences in flowering time between nearby individuals correlated with kinship coefficient, and earliness of flowering remained stable over time. A decrease in mean seed production per fruit with increasing flowering time suggests selection against late bloomers. However, germination rate was not affected by seed collection date, and the main seed disperser, the bat Eidolon helvum, seemed to increase in abundance at the end of the reproductive season and preferred trees in open habitats where early and late bloomers are expected. CONCLUSIONS The pairwise approach performs well in detecting IBT. The persistence of different mating pools in such a case may result from a trade off between selective forces during the mating and seed dispersal processes.

Effects of honey bee virus prevalence, Varroa destructor load and queen condition on honey bee colony survival over the winter in Belgium

Summary Since 1999, European beekeepers have reported increased mortality in overwintering honey bee, Apis mellifera L. colonies. Viral infections are often cited as the potential cause for increased mortality. Many honey bee viruses commonly occur within bee populations and in many cases infected colonies appear asymptomatic. There is increasing evidence that the global spread of Varroa destructor has resulted in a significant change in the prevalence, distribution and/or virulence of viruses causing mortality in honey bee colonies. We report here the first survey of the prevalence of five RNA bee viruses and their effect on overwintering survival of Belgian honey bee colonies. In the autumn of 2006, samples of adult bees were removed from 36 apiaries. Adult bee samples were analyzed by using RT-PCR for virus identification. Varroa mite prevalence in these samples was also quantified. A follow up visit of colonies in the spring permitted us to assess colony survivorship which permitted the effect, if any, of autumn varroa loads, virus presence and queen condition on colony survivorship to be ascertained. Although acute bee paralysis virus was the least prevalent of the detected honey bee viruses, it was strongly linked with increased colony mortality. Co-infection with more than two viruses also had an appreciable negative effect on colony survivorship.