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PubMed2000

Pest control by the release of insects carrying a female-killing allele on multiple loci.

With recent advances in genetics, many new strategies for pest control have become feasible. This is the second article in which we model new techniques for pest control based on the mass release of genetically modified insects. In this article we model the release of insects carrying a dominant and redundant female killing or sterilizing (FK) allele on multiple genetic loci. If such insects are released into a target population, the FK allele can become widely spread in the population through the males while reducing the population each generation by killing females. We allow the number of loci used to vary from 1 to 20. We also allow the FK allele to carry a fitness cost in males due to the gene insertions. Using a model, we explore the effectiveness and optimal strategies for such releases. In the most ideal circumstances (no density-dependence and released insects equal in fitness to wild ones), FK releases are several orders of magnitude more effective than equal sized sterile male releases. For example, a single release of 19 FK-bearing males for every two wild males, with the released males carrying the FK allele on 10 loci, reduces the target population to 0.002% of no-release size. An equal sized sterile release reduces the target population to 5% of no-release size. We also show how the effectiveness of the technique decreases as the fitness cost of the FK alleles in males increases. For example, the above mentioned release reduces the target population to 0.7% of no-release size if each FK allele carries a fitness cost in males of 5%. Adding a simple model for density-dependence and assuming that each of the released males carries the FK allele on six loci, we show that the release size necessary to reduce the target population to 1/100 of no-release size in 10 generations of releases varies from 0.44:1 to 4:1 (depending on parameter values). We also calculate the optimal number of loci on which to put the FK allele under various circumstances.

Alleles↗
PubMed2004

[The history of the flea in art and literature].

The flea has been, indirectly, one of the protagonists in the history of man. As one of the two vectors of Yersinia pestis, the etiological agents of the Black Death, the flea (Xenopsylla cheopis) has contributed, over the centuries, to the death of millions of people in many countries. Galileo Galilei was the first to observe the flea with a microscope (1624), but the credit of depicting it with a stunning drawing goes to the Britisher Robert Hooke in 1665. A number of zoologists, including Antonie Van Leeuwenhoek and Diacinto Cestoni, well described and illustrated the life cycle of the flea in the XVII century. Some of these reports inspired scholars such as J. Swift and J. Donne for the composition of classic poems. Also, the flea, alone and with its hosts, has inspired a number of artists to create fine paintings; among them: G. M. Crespi, G. B. Piazzetta, G. de la Tour and others. Colorful sonnets on the flea in the Roman dialect were written by G. Belli and Trilussa. The flea also, as a theme, inspired musicians such as G. F. Ghedini and M. Mussorgsky, play writers such as Feydeau and moviemakers such as Charlie Chaplin. The flea is, indissolubly, connected with the history of Black Death. This disease in man is, in fact, caused--as demonstrated by Yersin and Simond--by the triad: bacterium (Yersinia pestis)/rat/flea (Xenopsylla cheopis). Over the centuries, Black Death has had a deep impact on both the visual arts and literature and, as a result, a very large number of paintings and other works of art have been produced to remember these tragic episodes. In the field of literature, Black Death has been skillfully described by writers such as Boccaccio, Manzoni and Camus. Finally, in recent years, following the discovery of the existence of a large market for the control of fleas in small animals, the interest in this minute insect has been resurrected and, parallel to that, the rebirth of the flea iconography, through electromicroscopy, has also taken place.

Algeria↗
PubMed1999

[Bacillus thuringiensis: a biotechnology model].

This paper is on the different biotechnological approaches that have been used to improve Bacillus thuringiensis (Bt) for the control of agricultural insect pests and have contributed to the successful use of this biological control agent; it describes how a better knowledge of the high diversity of Bt strains and toxins genes together with the development of efficient host-vector systems has made it possible to overcome a number of the problems associated with Bt based insect control measures. First we present an overview of the biology of Bt and of the mode of action of its insecticidal toxins. We then describe some of the progress that has been made in furthering our knowledge of the genetics of Bt and of its insecticidal toxin genes and in the understanding of their regulation. The paper then deals with the use of recombinant DNA technology to develop new Bt strains for more effective pest control or to introduce the genes encoding partial-endotoxins directly into plants to produce insect-resistant trangenic plants. Several examples describing how biotechnology has been used to increase the production of insecticidal proteins in Bt or their persistence in the field by protecting them against UV degradation are presented and discussed. Finally, based on our knowledge of the mechanism of transposition of the Bt transposon Tn4430, we describe the construction of a new generation of recombinant strains of Bt, from which antibiotic resistance genes and other non-Bt DNA sequences were selectively eliminated, using a new generation of site-specific recombination vectors. In the future, continuing improvement of first generation products and research into new sources of resistance is essential to ensure the long-term control of insect pests. Chimeric toxins could also be produced so as to increase toxin activity or direct resistance towards a particular type of insect. The search for new insecticidal toxins, in Bt or other microorganisms, may also provide new weapons for the fight against insect damage.

Agriculture↗