Insect Genome Projects
The importance of insects
Insects are the largest animal group in the world (75% of all species are insects) and are economically and ecologically extremely important, because most flowering plants depend on insects for their pollination. The honey bees alone, for example, pollinate 15-20 billion dollars worth of crop yearly in the United States.
But insects can also be severe agricultural pests, destroying 30% of our potential annual harvest, and can be vectors (intermediate pathogen carriers) for major diseases such as malaria, sleeping sickness, Dengue fever, yellow fever, and elephantiasis (for a more complete list of insect-borne dideases see: http://www.traveldoctor.co.uk/insects.htm). There are an estimated 300-500 million cases of malaria and up to 2.7 million deaths (mainly children) from malaria each year. But also the other diseases are equally serious. Elephantiasis, for example, disables 130 million people worldwide and 1.1 billion people, 17% of the world's population, are at risk of infection.
It will be clear, therefore, that insects can be both very beneficial and harmful (pests) and that a few insect species are hampering the welfare of many hundreds of millions of people especially in the developing countries of the third world. Thus, vast social benefits would be gained, if one selectively could reduce the populations of these pest insects.
Which insects have been sequenced so far?
Although much sequencing efforts have been focused on the twelve Drosophila species (1-3), other important insects have also been sequenced during the last eight years (Fig. 1). These insect species are: the malaria mosquito Anopheles gambiae (sequenced and published, ref. 4); the silkworm Bombyx mori (sequenced and published, refs. 5 and 6); the honey bee Apis mellifera (sequenced and published, ref. 7); the red flour beetle Tribolium castaneum (sequenced and published, ref. 8); the yellow fever mosquito Aedes aegypti (sequenced and published, ref. 9); the mosquito Culex pipiens (sequenced, but unpublished); three parasitic wasp species, belonging to the genus Nasonia (sequenced, but unpublished); the blood-sucking bug Rhodnius prolixus (in progress); the pea aphid Acyrthosiphon pisum (in progress); and the body louse Pediculus humanus (in progress).
Fig. 1. Phylogenetic relationships of the insects, whose genomes have been sequenced. Green indicates genomes that have been fully sequenced (more than 8x coverage), blue indicates genomes, where the sequencing has not been completed (less than 8x coverage). The sequenced genomes cover about 350 million years of insect evolution.
These twenty-four species represent six different insect orders (Fig. 1) and also the two major evolutionary lineages of insects: Holometabola (insects with a complete metamorphosis) and Hemimetabola (insects having an incomplete metamorphosis). The sequenced genomes from these insects are goldmines, because they contain the information of all proteins and, thereby, of all biochemical and physiological processes that occur in an insect.
Why have these insects been selected for a genome project?
The twenty-four insect species have been selected for a genome project for different reasons. First, some insects are model organisms, such as the fruitfly D. melanogaster, which is a well-established model for geneticists and developmental and molecular biologists. The other Drosophila species have been sequenced to help with the interpretation of the D. melanogaster genome (2, 3).
A second class are the medically important insects that are vectors for serious diseases, such as malaria (the mosquito A. gambiae), yellow fever (the mosquito A. aegypti), elephantiasis (the mosquito C. pipiens), Chagas disease (the blood-sucking bug R. prolixus), and typhus (the body louse P. humanus).
A third class are the insects that are agriculturally important. To them belong agriculturally beneficial insects, such as the honey bee A. mellifera, which is a major pollinator of food plants and producer of honey, and the silkworm B. mori, which produces silk. In contrast to them, the red flour beetle T. castaneum (which destroys stored grain and many other dried and stored commodities for human consumption) and the pea aphid A. pisum (which causes severe damage to green food plants) are serious agricultural pests. The parasitic wasp N. vitripennis and the other two Nasonia species have been selected, because of their potentials for biological pest control (they lay eggs into a variety of agricultural pest insects).
1. Adams M.D., et al. (2000). The genomic sequence of Drosophila melanogaster. Science 287: 2185-2195.
2. Richards, S. et al. (2005). Comparative genome sequencing of Drosophila pseudoobscura: chromosomal, gene, and cis-element evolution. Genome Res. 15: 1-18.
3. Nature issue of 8 November 2007 (no. 716), containing 14 "News and Views", "Progress", "Reviews", "Articles", "Letters", "Commentaries", and "Essays" on the sequencing of 12 Drosophila genomes.
4. Holt R. A., et al. (2002). The genome sequence of the malaria mosquito Anopheles gambiae. Science 298: 129-149.
5. Xia Q., et al. (2004). A draft sequence for the genome of the domesticated silkworm (Bombyx mori). Science 306: 1937-1940.
6. Mita, K., et al. (2004). The genome sequence of silkworm, Bombyx mori. DNA Res. 11: 27-35.
7. Weinstock, G.M. et al. (2006). Insights into social insects from the genome of the honeybee Apis mellifera. Nature 443: 931-949.
8. Richards, S. et al. (2008). The genome of the model beetle and pest Tribolium castaneum. Nature 452: 949-955.
9. Nene, V., et al. (2007). Genome sequence of Aedes aegypti, a major arbovirus vector. Science 316, 1718-1723.
Last updated: 21-07-2009