Nathalie Mondy

Blending in with the crowd: social parasites integrate into their host colonies using a flexible chemical signature

Social parasites are able to exploit their hosts communication code and achieve social integration. For colony foundation, a newly mated slave–making ant queen must usurp a host colony. The parasites brood is cared for by the hosts and newly eclosed slave–making workers integrate to form a mixed ant colony. To elucidate the social integration strategy of the slave–making workers, Polyergus rufescens, behavioural and chemical analyses were carried out. Cocoons of P. rufescens were introduced into subcolonies of four potential host species: Formica subgenus Serviformica (Formica cunicularia and F. rufibarbis, usual host species; F. gagates, rare host; F. selysi, non–natural host). Slave–making broods were cared for and newly emerged workers showed several social interactions with adult Formica. We recorded the occurrence of abdominal trophallaxis, in which P. rufescens, the parasite, was the donor. Social integration of P. rufescens workers into host colonies appears to rely on the ability of the parasite to modify its cuticular hydrocarbon profile to match that of the rearing species. To study the specific P. rufescens chemical profile, newly emerged callows were reared in isolation from the mother colony (without any contact with adult ants). The isolated P. rufescens workers exhibited a chemical profile closely matching that of the primary host species, indicating the occurrence of local host adaptation in the slave–maker population. However, the high flexibility in the ontogeny of the parasites chemical signature could allow for host switching.

The response of the grape berry moth (Lobesia botrana) to a dietary phytopathogenic fungus (Botrytis cinerea): the significance of fungus sterols.

A Tortricidae (Lobesia botrana) has a mutualistic relationship with the fungus (Botrytis cinerea). In this study, we investigated the growth, survival, fecundity and amount of sterols and steroids in larvae of this vineyard pest reared on artificial diets containing mycelium (3%) or purified sterols (0.01%) of the phytopathogenic fungus. Two principal questions related to the physiological and biochemical basis of this mutualistic relationship were addressed: (1) how the fungus influences growth, survival, fecundity, sterol and steroid contents of the insect and (2) are fungal sterols involved in the biochemical basis of mutualism? The presence of fungus in the diet led to a decrease of total duration of larval development (mean gain 5.1-9.4 days compared to the total duration in control of 42.9 days), an increase in survival (mean gain 50-76.3%) and fecundity (gain of 94-102%). These positive effects of the fungus on the biology and physiology of the insect were directly correlated to the presence of fungal sterols in the diet. Fungal sterols are one of the biochemical basis of the mutualistic relationship between L. botrana and B. cinerea.

Effect of onion consumption by rats on hepatic drug-metabolizing enzymes

Fruits and vegetables or their natural constituents which increase detoxication enzymes and/or reduce activating enzymes are considered as good candidates to prevent chemically-induced carcinogenesis. In this study, rats were fed a diet supplemented with 20% onion powder for 9 days. Several cytochrome P450 (CYP)s enzymes (CYP 1A, 2B, 2E1, 3A), which are involved in carcinogen activation, were determined by measuring their enzyme activities using specific substrates. In addition, phase II enzymes activities such as UDP-glucuronosyltransferase (UGT) and glutathione S-transferase (GST), involved in detoxication of carcinogens, were measured. Protein levels of CYPs and GST A1/A2, A3/A5, Ml, M2 and P1 were measured using antibodies in Western blots. Consumption of onion induced CYP 1A and CYP 2B activities while it decreased CYP 2E1 activity. This later modification was accompanied by a decrease of CYP 2E1 levels. The same dietary treatment caused a slight increase of the total GST activity. The relative proportions of GST subunits were modified. GST Al/A2 subunits were increased while GST A3/A5 and GST M2 subunits were decreased and GST M1 and P1 were not modified. Onion consumption also increased p-nitrophenol UGT activity. Taken together, these results suggest that the decrease of CYP 2E1 and the increase of phase II enzymes by onion can afford protection against some carcinogens, while the decrease of some GST subunits could increase the genotoxic effects of other chemicals. The modulating effect of onion could be ascribed to alk(en)yl polysulphides and/or glycosides of flavonols, which were identified in the onion powder.

Aroma analysis of fresh and preserved onions and leek by dual solid-phase microextraction–liquid extraction and gas chromatography–mass spectrometry

The lachrymatory factor (thiopropanal-S-oxide) was directly analysed on fresh onion (Allium cepa) juice by solid-phase microextraction (polyacrylate fibre) using a fast routine GC-MS method on a 10 m x 0.32 mm I.D. (4 microm thick polydimethylsiloxane film) column with splitless mode injection. The identification and quantification of thiosulphinates and zwiebelanes were obtained on the same juice extracted by diethyl ether after 80 min maceration using the same GC-MS method. Selected ion recording enhanced the differentiation possibilities and the detection limits. This dual method was used to evaluate flavour differences between onion and shallot varieties as it provides accurate profiles of all initially formed compounds. Moreover, this method allowed us to compare qualitatively and quantitatively transformed products: frozen, freeze-dried powders and sterilised products. Excepting the lachrymatory factor, frozen onion compounds were similar compared to those of fresh onion sample. Conversely, the other transformed samples have lost most of the initially formed compounds and produced mainly di- and trisulphides corresponding to the degradation of thiosulphinates and zwiebelanes. These dramatic changes can explain the very different flavours of these manufactured products compared to fresh material.

Olfactory and gustatory behaviour by larvae of Lobesia botrana in response to Botrytis cinerea

In vineyards, larvae of Lobesia botrana (Denis and Schiffermüller) (Lepidoptera: Tortricidae) and Botrytis cinerea (Persoon: Fries) often occur together. This study was carried out to establish whether first instar larvae are attracted by the fungus. Olfactory and gustatory responses of larvae to the fungus were investigated on grape berry clusters (Vitis vinifera) and in two types of olfactometer. In clusters infected partly by B. cinerea, 82% of first instar larvae settled where berries had been infected. In the olfactometers, first instar larvae detected and discriminated between two tested foods. They significantly preferred synthetic media or grape berries (cv., ‘Alphonse Lavallée’ or ‘Cabernet Sauvignon‘) infected with B. cinerea to non‐infected controls. The olfactory response led to 62.2% to 72.6% of the first instar larvae attracted by the fungus and the association of olfactory with gustatory responses resulted in similar rates (64.1% to 81.6%). So, the larvae were most attracted by synthetic media or grape berries infected by the fungus as compared to the controls. Olfaction appears to be the main sense involved in this attraction process.

Mutualism between a phytopathogenic fungus (Botrytis cinerea) and a vineyard pest (Lobesia botrana). Positive effects on insect development and oviposition behaviour

Abstract In vineyards, larvae of the grape berry moth ( Lobesia botrana ) favour the development of the grey mould fungus Botrytis cinerea . To study the possibility of a mutualistic relationship between these organisms, we investigated the effects of the fungus on the development and oviposition behaviour of the insect. Larvae were reared on whole plants infected or uninfected with the fungus, or on an artificial diet containing either infected grape berries or the mycelium. The presence of the fungus consistently led to a reduction in the duration of insect development (4–6 d) and mortality (20–67 %). The fecundity increased from 12 to 76 %. Moreover, the fact that the females laid eggs preferentially on fungus-infected grape berries confirms the mutualistic association between these organisms. The fungus alone contributed to the positive effects. We showed the existence of a mutualistic relationship between the two organisms which are both damaging to vineyards.

Possible interest of various sample transfer techniques for fast gas chromatography-mass spectrometric analysis of true onion volatiles.

We improved GC-MS analysis of onion volatiles by comparing organic solvent partition with solid-phase microextraction (SPME) following cryo-trapping isolation and by comparing the same extraction methods on direct onion juice. Cryotrapping produces very small quantities of volatiles and therefore is not a suitable extraction method for GC-MS analysis. We confirm that SPME accelerates the degradation of labile thiosulfinates but the lacrymatory factor remains intact. The identification of Allium thiosulfinates is only obtained on juice extracted by diethyl ether using a fast GC-MS analysis on a 10 m X 0.3 mm column of 4 microm coating, with routine splitless injection. The lacrymatory factor is best analysed directly on fresh onion juice by SPME with the same chromatographic conditions. To characterise and to quantify all the true onion volatiles, we propose to analyse the same sample by successive SPME-GC-MS and solvent extraction-GC-MS.

Feeding insects with a phytopathogenic fungus influences their diapause and population dynamics

Abstract.  1. A facultative mutualistic relationship between a herbivorous moth, Lobesia botrana, and a phytopathogenic fungus, Botrytis cinerea, both damaging the same plant, the vine, has been demonstrated recently. Laboratory and field studies were carried out to determine the influence of the presence of the fungus in food on larvae during the pre‐ and post‐diapause periods and on the global fitness of the insect.

Comparison of GC-MS and HPLC for the analysis ofAllium volatiles

SummaryVolatile sulfur compounds produced enzymatically fromAllium species have been identified by combined gas chromatography-mass spectrometry (GC-MS) and the results obtained have been compared with those from HPLC-UV analysis (with a diode-array detection, DAD). Analysis of the same onion sample by successive SPME-GC-MS or by solvent extraction then GC-MS enabled us to identify the true onion volatiles including lachrymatory factor and thiosulfinates. Conversely, for garlic samples HPLC analysis is more suitable because of the substantial degradation of allicin (the main thiosulfinate in garlic) during GC. An El mass spectrum of allicin obtained by GC-MS is reported for the first time.

Effects of the ingestion of Serratula tinctoria extracts, a plant containing phytoecdysteroids, on the development of the vineyard pest Lobesia botrana (Lepidoptera: Tortricidae)

We describe here the effects of extracts from Serratula tinctoria, a plant producing phytoecdysteroids, on the growth and development of Lobesia botrana, an economically important pest in vineyards. Leaves, hairy roots, or semi-purified (by Sep-Pak procedure) methanolic extracts from this plant were incorporated into an artificial diet given to insects. Larval growth, mortality, weight, and sex-ratio were investigated, as well as sterol and ecdysteroid contents. Experimental diets induced an important mortality in the first, second, and third larval instars, but also in pupae. As males appeared more sensitive to extracts, sex ratio was significantly modified on experimental diets (particularly with Sep-Pak fractions SP60, SP80, and SP100). Pathophysiological effects were also observed: Larval development was significantly faster on experimental diets and a weight loss, 14% for males and from 12% to 22% for females, was noted (particularly when reared on hairy roots and SP20, SP60, and SP80 extracts). Moreover, sterol and ecdysteroid contents were disturbed after rearing on experimental diets. Arch. Insect Biochem. Physiol. 35:227–235, 1997.