Effects of feeding frequency and sugar concentration on behavior and longevity of the adult parasitoid: Aphidius ervi (Haliday) (Hymenoptera: Braconidae).

76 ref. doi: 10.1016/j.biocontrol.2004.07.013Aphidius ervi (Haliday) (Hymenoptera: Braconidae) is a solitary aphid endoparasitoid. Adults feed on honeydew and possibly on other sugar sources such as nectar. Sugar sources can vary qualitatively and quantitatively according to biotic factors and environmental conditions. Experiments were conducted to determine the influence of quantitative variations of sugar sources on survival, feeding behavior, and consumption of A. ervi. A 1:1 glucose–fructose mixture was tested in a range of concentrations (0–70% (w/v)). The lifetime of both sexes increased significantly with increasing sugar concentration. The optimal lifetime was achieved by insects fed with 50 and 70% (w/v) of sugar solution for males and 70% (w/v) for females. Behavioral studies showed that sugar concentrations had a significant influence on feeding duration: for males and females feeding duration increased with sugar concentration. Longevity primarily depended on the concentration of the sugar solution, rather than the quantity of sugar solution ingested. In the last experiment, we studied the effect of feeding intervals on the lifetime of A. ervi females. Females fed with a 50% (w/v) 1:1 glucose–fructose mixture continuously or twice a day lived eight times longer than unfed parasitoids. In contrast, females fed every two days lived only half as long as those fed daily. We can thus conclude that females need at least two food intakes per day to attain maximum longevity. Our results provide insight into the nutritional requirements of A. ervi under laboratory conditions. Such information can be a basis to improving the longevity of this biocontrol agent by sugar feeding in the field and in greenhouses

Soybean proteinase inhibitor and the foraging strategy of free flying honeybees

Previous laboratory studies reported disruption of the digestive physiology and learning behaviour in individual honeybees treated with Bowman-Birk inhibitor (BBI), a serine proteinase inhibitor expressed in some GM plants. Our objective was to detect behavioural effects of this transgene on honeybees at the colony level, maintained in laboratory conditions. We set up a choice experiment, based on 150 free-flying individuals which performed a over 7700 visits on the flowers. The mean number of visits per hour, the mean time spent on the feeder and the interval between consecutive visits were not significantly different when the feeding sucrose solution was mixed with BBI at 100 μg·mL–1, a dose close to the expression level in planta. The methodology proposed herein could form a colony scale procedure particularly relevant to the risk assessment of the impact on bees of proteinase inhibitors or other transgenes to be possibly expressed in melliferous plant

Integration of a Recombinant Chitinase into Bacillus thuringiensis Parasporal Insecticidal Crystal

Chitinases have been successfully used in combination with Bacillus thuringiensis delta-endotoxins forming crystals in order to enhance their insecticidal activities. In this context, we opted for promoting the chitinase integration into these crystals. Thus, we engineered, for the first time, a fusion protein (CDF) consisting of the chitinase Chi255 and the carboxy-terminal half of Cry1Ac, both from B. thuringiensis subsp. kurstaki. The constructed transcriptional fusion (chi255Δsp-CTcry1Ac) was cloned into a shuttle vector (Escherichia coli/B. thuringiensis) downstream the sporulation-dependent promoters BtI-BtII and upstream the cry1Ac transcription terminator. The resulting plasmid, named pF, was transferred by electroporation to crystalliferous B. thuringiensis strain BNS3 and acrystalliferous strain BNS3Cry-. The functionality of the chimerical chitinase was demonstrated by an improvement of the relative chitinolytic activity of the recombinant strain BNS3/pF by 2.5 folds. Western blot analyses showed that, despite of the instability of CDF when expressed in the acrystalliferous strain, the C-terminal half of Cry1Ac succeeded to allow the integration of the chimerical chitinase into the crystal of BNS3. The recombinant strain BNS3/pF (LC(50) = 144.06 μg g(-1)) was 1.5 times more active against Ephestia kuehniella larvae than the wild strain (LC(50) = 212.10 μg g(-1)).Tunisian Ministere de l’Enseignement Superieur et de la Recherche Scientifique (MESRS

New Bacillus thuringiensis toxin combinations for biological control of Lepidopteran larvae

Cyt1Aa from Bacillus thuringiensis israelensis is known by its synergistical activity with B. thuringiensis and Bacillus sphaericus toxins. It is able to improve dipteran specific toxins activity and can prevent or overcome larval resistance to those proteins. The objective of the current study was to investigate the possible improvement of larvicidal activity of B. thuringiensis kurstaki expressing heterogeneous proteins Cyt1A and P20. cyt1A98 and p20 genes encoding the cytolytic protein (Cyt1A98) and the accessory protein (P20), respectively, were introduced individually and in combination into B. thuringiensis kurstaki strain BNS3. Immunoblot analysis evidenced the expression of these genes in the recombinant strains and hinted that P20 acts as molecular chaperone protecting Cyt1A98 from proteolytic attack in BNS3. The toxicities of recombinant strains were studied and revealed that BNS3pHTp20 exhibited higher activity than that of the negative control (BNS3pHTBlue) toward Ephestia kuehniella, but not toward Spodoptera littoralis. When expressed in combination with P20, Cyt1A98 enhanced BNS3 activity against E. kuehniella and S. littoralis. Thus, Cyt1Aa protein could enhance lepidopteran Cry insecticidal activity and would prevent larval resistance to the most commercialized B. thuringiensis kurstaki toxins.Tunisian Ministry of Higher Education and Scientific Research

Effects of potato plants expressing the NPTII-gus fusion marker genes on phhysiology and exploratory behaviour of the peach-potato aphid Myzus persicae.

Transgenesis developed in the last 20 years offers new possibilities for crop protection. The transgenic process, however, requires the use of marker fusion genes to select and visualize the transformed tissues. Although the expression products of these marker genes are stably expressed in crops, little attention has been given to assess the eventual risks of these recombinant proteins on phytophage populations. Three independent transgenic potato (Solanum tuberosum) clones from the cultivar Désirée (DG5, DG18, and DG20) carrying the commonly used nptII-gus gene construct and exhibiting different β-glucuronidase activity (0.843 ± 0.011, 0.576 ± 0.096, and 0.002 ± 0.000 pmol min-1.mg-1, respectively) were evaluated to determine the impact of the encoded proteins on the behaviour, development, reproduction, and demography of the peach-potato aphid, Myzus persicae, under laboratory-controlled light and temperature. Our results revealed that the transgenic event can alter aphid physiology or behaviour. Experiments showed a probiotic effect of one transgenic line, the DG5, resulting in reduced prereproductive period and mortality, and enhanced daily fecundity, which was expressed in a greater population growth potential (rm = 0.205 vs. rm = 0.174 of the control). In contrast, aphids fed with the DG18 line exhibited reduced adult survival and reproductive period but no alteration of their demographic parameters (rm = 0.176). Finally, no physiological alteration was induced in aphids fed on a DG20 diet (rm = 0.170). Behavioural experiments conducted in a 4-choice olfactometer demonstrated that insects were significantly more attracted by the odour of transgenic DG18 potato plant than that of Désirée non-transformed plant, spending twice as much time in the DG18 plant odour. The two other transformed clones (DG5 and DG20) were as attractive as the non-transformed cultivar. It is concluded that the β-glucuronidase expression in potato plants might be responsible for the probiotic effect measured on the feeding aphids, whereas alteration of the foliage odour would result from a pleiotropic effect