Lethal and sub-lethal effects of thymol on honeybee (Apis mellifera) larvae reared in vitro

BACKGROUND

Thymol offers an attractive alternative to synthetic chemicals to keep Varroa under control. However, thymol accumulates in bee products and is suspected of having adverse effects on colonies and especially on larvae. In this study, we investigated the effects of acute and chronic exposure to thymol on larvae reared in vitro with contaminated food and compared results to the theoretical larval exposure based on the amount of pollen and honey consumed by larvae during their development.

RESULTS

The laboratory assays reveal that, first, the 48 h-LD50 of thymol introduced into larval food is 0.044 mg larva(-1) . Second, the 6 day-LC50 is 700 mg kg(-1) food. A significant decrease of larval survival and mass occurred from 500 mg thymol kg(-1) food (P < 0.0001). Finally, vitellogenin expression, which reached a maximum at the fifth instar larvae, is delayed for individuals exposed to 50 mg thymol kg(-1) food (P < 0.0006). That is 10 times higher than the theoretical level of exposure.

CONCLUSION

Based on the level of thymol residue found in honey and pollen, these results suggest that the contamination of food by thymol represents no notable risk for the early-developing larvae.

Artificial feeding of Varroa destructor through a chitosan membrane: a tool for studying the host-microparasite relationship

Rearing pests or parasites of very small size in the absence of their living host is a challenge for behavioural, physiological and pathological studies. For feeding Varroa destructor, an ectoparasitic mite of Apis mellifera, a confinement space with a membrane separating the nutritive solution and the space was designed. The mite measures less than 2 mm and bears a perforating apparatus with a length of 15 μm. The membrane, an essential element of the chamber, has a thickness of 0.1 μm, and is made of chitosan. It closes one face of the individual confinement chamber and allows piercing and the ingestion of the nutritive solution. Factors inducing feeding can be applied on the inner walls or on the membrane. In the particular case of Varroa, the highest percentages of feeding mites are obtained by addition of host haemolymph to the nutritive solution, suggesting the kairomonal role of haemolymph in addition to its nutritional one. The membrane concept can be easily applied to several mites or other micro-pests.

Reconstructed interfollicular feline epidermis as a model for Microsporum canis dermatophytosis

Microsporum canis is a pathogenic fungus that causes a superficial cutaneous infection called dermatophytosis. The complexity of mechanisms involved in dermatophytic infections makes relevant in vivo studies particularly difficult to perform. The aim of this study was to develop a new in vitro model of M. canis dermatophytosis using feline fetal keratinocytes in reconstructed interfollicular epidermis, and to investigate its relevance in studying the host-pathogen relationship. Histological analysis of reconstructed interfollicular feline epidermis (RFE) revealed a fully differentiated epidermis. A proliferation assay showed replicating cells only in the basal layer, indicating that RFE is a well-stratified living tissue, leading to the formation of a horny layer. Histopathological analysis of RFE infected by M. canis arthroconidia revealed that the fungus invades the stratum corneum and produces SUB3, a keratinase implicated in the infectious process. In view of these results, an M. canis dermatophytosis model on RFE seems to be a useful tool to investigate mechanisms involved in natural M. canis feline infections.

Effect of phenotypic variation inXenorhabdus nematophilaon its mutualistic relationship with the entomopathogenic nematodeSteinernema carpocapsae

The entomopathogenic nematodeSteinernema carpocapsaeis mutualistically associated with the bacteriumXenorhabdus nematophila. Infective Juveniles (IJs) transportX. nematophilacells that provide them with good conditions to reproduce within the insect. In the laboratory, long term stationary-phase culture conditions sometimes leadX. nematophila's variant 1 cells, which were previously isolated from the worms, to spontaneously and irreversibly change into a new phenotypic variant (variant 2). In this paper, we tested the ability of each phenotypic variant to (i) be transmitted by IJs, (ii) to optimize the worm's fitness within the insect, and (iii) to counteract the effect of closely related antagonistic bacteria previously shown as being able to totally preventS. carpocapsae's reproduction within the insect. We found that IJs did associate with cells of both phenotypes but that the variant 2 cells were preferentially retained by the nematodes when both variants were present in the insect. Both phenotypic variants led to the same fitness ofS. carpocapsaein insects not infected by antagonistic bacteria. In insects infected by antagonistic bacteria, both variants were able to provide protection toS. carpocapsae. Nevertheless, this protection depended on the phenotypic variant and the antagonistic bacteria that were co-injected into the insect. Further analysis conducedin vitroshowed that this variability could be partly linked to the sensitivity of each antagonistic bacterium to xenorhabdicin, produced byX. nematophila.

[Management in pollinosis and false pollinosis]

Typical cases of pollen allergen (hayfever, allergic asthma), together with isolated non-respiratory "equivalent" manifestations (urticaria, eye conditions, headache, etc.), are easy to detect on the basis of skin tests and the clinical history. Such manifestations may also occur in "false pollen allergy", related in most instances by atmospheric moulds (Dematiaceae), sometimes by house dust or dermatophytes (Candida Albicans, Trichophyton sp), by food or by a bacterial infection or allergy. A combination of pollen allergy and false pollen allergy is common. In cases of false pollen allergy the proportion of negative skin reactions would appear to worsen with the repeated use of prolonged action corticosteroid injections, given on a preventive basis. Similarly, these disorders, initially seasonal, change to more chronic manifestations throughout the year. Desensitization with aqueous extracts of allergens ensured the most complete protection against the causes of pollen allergy and false pollen allergy. Allergen extracts percipitated with alun (semi-retard extracts), more effective than tyrosine adsorbates (Pollinex) have the advantage of offering more rapid treatment without the risk of dangerous reactions. The best therapeutic results have obtained over the course of the last ten years, by the authors, combining on each occasion a semi-retard allergen with an aqueous allergen, thereby acquiring the benefit of the adjuvant effect of the first, in a course of ten to fifteen injections per year. Non specific therapy (antihistamines, cromoglycate, theophylline, etc.) retains all of its symptomatic indications. Oral corticosteroid therapy is better metabolized in the organism and has less of a disturbing effect on the circadian rhythm of cortisol, and is hence to be preferred to injections of delyaed action corticosteroid suspensions.