Establishment of fungal entomopathogens Beauveria bassiana and Bionectria ochroleuca (Ascomycota: Hypocreales) as endophytes on artichoke Cynara scolymus.

Entomopathogenic fungi (EPF) are commonly found in diverse habitats and are known to cause mycoses in many different taxa of arthropods. Various unexpected roles have been recently reported for fungal entomopathogens, including their presence as fungal endophytes, plant disease antagonists, rhizosphere colonizers and plant growth promoting fungi. In Tunisia, a wide range of indigenous EPF isolates from different species, such as Beauveria bassiana and Bionectria ochroleuca, were found to occur in the soil, and to be pathogenic against the artichoke aphid Capitophorus elaeagni (Hemiptera: Aphididae). Since endophytic fungi are recently regarded as plant-defending mutualists and their presence in internal plant tissue has been discussed as an adaptive protection against insects, we were interested on elucidating the possible endophytic behavior of B. bassiana and B. ochroleuca on artichoke, Cynara scolymus, after foliar spraying tehcnique. The leaf spray inoculation method was effective in introducing the inoculated fungi into the plant tissues and showed, then, an endophytic activity on artichoke even 10 days later. According S-N-K test, there was significant differences between the two fungal treatments, B. ochroleuca (84% a) and B. bassiana (78% a), and controls (0% b). Likewise, the inoculated entomopathogenic fungi were also isolated from new leaves even though with significant differences respectively between controls (0% c), B. bassiana (56% b) and B. ochroleuca (78% a). These results reveals significant new data on the interaction of inoculated fungi with artichoke plant as ecological roles that can be exploited for the protection of plants.

Insect growth regulator activity of Cestrum parqui saponins: an interaction with cholesterol metabolism.

Cestrum parqui is an ornamental shrub known for its insecticidal activity against some insect pests; this activity comes from the crude saponic extract of the leaves of this plant, the saponins cause insect growth regulator symptoms (development and moulting perturbation). In this work we try to demonstrate the hypothesis that saponins interact with ecdysone (moulting hormone) synthesis mechanisms by reducing diet cholesterol absorption (cholesterol forms the skeleton of ecdysone and of other ecdysteroids). To show the cholesterol/saponin interaction we used a stored product pest insect (Tribolium confuisurn), the larva of this insect are affected by saponins added in their diet, but the addition of cholesterol permits to reduce significatively this insecticidal propriety. Using Spodoptera littoralis larva model the tentative to detect a cholesterol rate reduction on the level of hemolymph is also unsuccessful. All these experiments shows that this type of reaction can't occur in the diet or in the digestive system but probably in insect cells. It is clear that Cestrurn parqui saponins affect the cholesterol metabolism but the exactly mechanism is still unknown. More investigations are necessary to develop this hypothesis and to envisage the use of Cestrum saponins as insect growth regulator bioinsecticide.

Biological control of Aphis gossypii on pepper plant using Coccinella algerica.

To calibrate biological control in pepper plant against Aphis gossypii using Coccinella algerica different experimentation were made. The consumption of C. algerica during the larval stage was enumerated in laboratory conditions. The densities (1, 4, 8 larvae/plant) to L2 stage of C. algerica necessarily to decrease aphid's populations were determined in plant pepper and the daily consumption in the pepper plant at the different densities was calculated. The density with 8 larvae at semi natural conditions is higher significantly. In protected crop of pepper, different releases to C. algerica were made with eggs, second stage larva and with ladybird before infestation with A. gossypii. A strategy to introduce L2 stage is preferred than the release with punters of C. algerica at different densities. At the same, the Introduce L2 stage is compared to release the C. algerica ladybird before the infestation of A. gossypii in the protected crops. The activity of ladybird has been maintained in the protected crop and it was shown when the infestation appeared.

Bio-insecticidal activities of halophytic plant extracts against Tribolium confusum (Coleoptera, Tenebrionidae).

Salt marsh plants were tested for their insecticidal activities against larvae of the confused flour beetle Tribolium confusum (Tenebrionidae). 16 aerial part extracts were obtained using organic solvents of increasing polarity and tested for their anti-feedant and toxicity effects. Responses varied with plant material and extract type. Ethyl acetate extracts of F. laevis, S. echioides and. T. boveana and petroleum ether extract of F. laevis presented, anti-feedant property. However, S. fructicosa seemed to be attractive to the tested flour beetle. Mortalities of 97, 87, 97 and 80% were observed by using respectively ethyl acetate extracts of F. laevis, S. echioides and T. boveana and petroleum ether extract of F. laevis, when applied at a dose of 1%, mixed with the insect diet. This preliminary study showed that F. laevis, S. echioides and T. boveana presented potential bio-insecticidal activity with ethyl acetate extracts, similar result was found with petroleum ether extract of F. laevis. More complementary studies are needed for the use of these extracts to control T. confusum.

Bioactivities of seven chrysanthemum species flowers powder on Spodoptera littoralis (Boiduval) larvae.

We have screened seven Chrysanthemum species, collected from different biotope in Tunisia for the antifeeding and growth regulatory activity against S. littoralis (Lepidoptera: Noctuidae) an insect pest of tomato. The flowers powder was added to the Poitout and Bues (1974) artificial diet at three concentrations: 4, 8, and 16%. After ten days of treatment, the consumed quantity determination revelled that these species have an antifeeding activity proportional to the concentration, more considerable for the C. fuscatum and C. Myconis flowers powder. At the concentration of 16% the larvae weight was significantly delayed in the average time to the control, these results were compared to the effect of Cestrum parquii on S. littoralis and Pieris brassicae The moulting date determination showed an elongation of the third, fourth and fifth stages at the high concentration probably due to the presence of juvenile hormones Analogues.

[The effect of food containing Cestrum paquii (Solanaceae) extract on various damaging Lepidoptera]. / L'impact de l'alimentation contenant du broyât de Cestrum paquii (Solanacées) sur des lépidoptères dommageables.

The repulsive activity of Cestrum parquii on the feeding behaviour of Pieris brassicae L. and Spodoptera littoralis Boisduval was studied. Antifeedant effect was observed at regular intervals during a week. Meal uptake was stopped after the first day, showing a strongly antifeedant effect of C. parquii extract on these two species. The impact of C. parquii with different concentrations of dry extract (2, 4, 8, 16, 32%) delayed the larval growth of Spodoptera littoralis Boisduval compared to untreated insects. Abnormal metamorphosis was observed with concentrations of 8 and 16% leading to death and abnormal morphogenesis. The antifeedant activity of C. parquii was also observed in S. littoralis and measured by the evolution of food uptake and the weight of larva. Effect seemed to be proportional to extract concentration in the diet. High concentration (32%) stopped growth in the earlier instar.