Hervé Mauléon

Pathogenicity of 17 isolates of entomophagous nematodes (Steinernematidae and Heterorhabditidae) for the ticks Amblyomma variegatum (Fabricius), Boophilus microplus (Canestrini) and Boophilus annulatus (Say)

Entomopathogenous nematodes are well known biocontrol agents of insects. They live in the superficial layer of the soil, a location where ticks accomplish their molt and where they oviposit their eggs, making them, theoretically, the preys of infective larvae of nematodes. Seventeen strains of entomopathogenous nematodes: eight strains of Steinernema and nine strains of Heterorhabditis were placed in contact with each of the free living stages of three tick species: Amblyomma variegatum, Boophilus microplus and B. annulatus. The first two species were resistant to all the nematode strains that were tested, whereas B. annulatus was susceptible to all of them. Ovipositing females were more susceptible than females during the preoviposition period. There were no anatomical differences between the two species of Boophilus which can account for such differences in their susceptibility. The use of nematodes to control some species of ticks should be considered.

Predators of the tick Amblyomma variegatum (Acari: Ixodidae) in Guadeloupe, French West Indies.

Some vertebrate species in Guadeloupe are predators of free or parasitic stages ofAmblyomma variegatum (Fabricius). Among birds, 1.9% of the 421 identified animals found in the stomachs of grackles (Quiscalus lugubris), 1.6% of the 364 animals found in the stomachs of free-ranging chickens, and 0.3% of the 4642 animals found in the stomach of cattle egrets (Bubulcus ibis) wereA. variegatum ticks. The most efficient predator of ticks was the tropical fire ant,Solenopsis geminata, which was observed to only attack engorged stages of ticks. An average of 8% of the 564 individual ticks or batch of ticks released on the ground, mainly in a grass environment, were attacked by this ant species. Mice (Mus musculus) and mongooses (Herpestes auropunctatus) feed on engorged nymphs and female ticks. None of the 15 strains of entomophagous nematodes, generaSteinernema andHeterorhabditis, experimentally put in contact with engorged larvae and nymphs were able to parasitize them. In the laboratory, the insectsMegaselia scalaris (Diptera) andTineola sp. (Lepidoptera) were occasionally found to feed on engorged and unfed ticks, respectively.

Dermal gland secretions of tropical bont tick,Amblyomma variegatum (Acarina: Ixodidae): Biological activity on predators and pathogens.

When they are mechanically disturbed, all instars of the tropical bont tickAmblyomma variegatum exude droplets of a liquid on the dorsal, lateral, and ventral cuticle. These spread out and quickly evaporate. In this study, the possible role of these secretions was investigated in relation to predators and pathogens. In laboratory bioassays, it was demonstrated that the secretions from engorged larvae, nymphs, and females have an antibiotic activity against the bacteria speciesBacillus thuringiensis andSerratia marcescens, combined with a repellent effect on a potential predator, the fire-antSolenopsis geminata.

Natural occurrence of entomopathogenic nematodes (Rhabditida: Steinernematidae) on golf courses in eastern Canada

A survey of entomopathogenic nematodes from 38 golf courses was conducted in different climatic areas of Ontario and Quebec provinces, Canada, during autumn 2002 and 2003. Soil samples were collected on golf course greens, fairways and roughs. Entomopathogenic nematodes were isolated from soil using wax moth (Galleria mellonella) and carrot weevil (Listronotus oregonensis) larvae as bait. Of the 436 samples (218 sites), 11 contained entomopathogenic nematodes for this study. All entomopathogenic nematode-positive samples were isolated from roughs. Isolates were characterised using DNA satellite probes and 28S rDNA sequence data. Both methods confirmed the identities of nematode isolates as Steinernema carpocapsae, S. feltiae and S. kraussei.

Spatial and temporal distribution of Heterorhabditis indica in their natural habitats of Guadeloupe

The presence of Heterorhabditis indica in the littoral zone of continental Guadeloupe was assessed by the Galleria trap technique. A total of 309 samples from 192 sampling sites were analysed. Heterorhabditis indica was found in 74 samples from 53 sites (45 beaches and eight limestone cliffs). The ecological characteristics of these places (climate, soil, flora and fauna) were described and the arthropods occupying these locations were tested for their ability to support nematode development. The spatial distribution of H. indica showed that the colonisation of these sites by nematodes is due to a permanent occurrence of patches generally found under the canopy of trees. An annual monitoring (performed in the wet season from 1996-2005) showed that these patches were regularly recovered (10 consecutive years). The population dynamics of H. indica was studied monthly in two sites for 28 months. In both sites, the abundance of nematodes was directly correlated to rainfall. In the dry season, when the soil moisture was lower than 3.5%, nematodes were not detected by the insect traps. The infective juveniles can survive about 6-7 months in such an environment. Field experiments with sterilised soil showed that nematode-free soil is normally recolonised by active migration but recolonisation can also occur when this route is excluded, indicating either infected insects or passive transport (human or animal) as alternative routes.

BACTERIA MODULATE THE DEGREE OF AMPHIMIX OF THEIR SYMBIOTIC ENTOMOPATHOGENIC NEMATODES ( Heterohabditis spp) IN RESPONSE TO NUTRITIONAL STRESS

Abstract. Facultatively sexual entomopathogenic nematodes are a promising model for the experimental study of the adaptive values of sex. Our experiments in the laboratory showed that entomopathogenic nematodes display at least two different strategies in regulating the degree of amphimix as a response to nutritional stress. One strategy promotes the production of males, amphimix and the genetic variability of the offspring, improving the chances for a successful new adaptation. Another strategy increases the production of hermaphrodites at the expense of males, increasing the total number of reproductive individuals and thus the total number of offspring produced. Surprisingly, the strategy used depends upon the strain of symbiotic bacteria the nematodes are growing. The relevance of the results, in helping to discriminate between rival theories for the evolutionary maintenance of sex, is discussed.