Insects

1. Bombyx mori
2. Drosophila melanogaster
3. Anopheles gambiae
4. Apis mellifera
5. Tribolium castaneum

Bombyx mori

Chromosome number : 2n=56

Genome

B. mori has an estimated 530-Mb haploid nuclear genome size, shared among 28 chromosomes. A large and diverse collection of genetic markers have been developed and mapped. The combined maps contain more than a thousand genetics markers, at an average spacing of 2-cM (or about 500-Kb). A physical map is being constructed, by restriction-fragment fingerprinting and end-sequencing of bacterial-artificial-chromosome (BAC) clones.

Chinese genome sequencing (5.93 X, ≈428.7 Mb) is from a male (ZZ) of an inbred domesticated variety, Dazao, a tropical bivoltine four-molter race commonly used for biological and genetic research around the world. Samples came from the posterior silk gland, fifth-instar day 3, on a mix of 1225 individuals. A whole genome shotgun (WGS) technique was used. Chinese assembly contains 90.9% of 212 known silkworm genes (with full-length cDNA sequence), 90.9% of 16,425 EST clusters, and 82.7% of 554 known genes from other Lepidoptera.

Japanese genome sequencing (3 X, ≈424 Mbp) is also by whole genome shotgun sequencing (WGS) strategy. As a result, a total of about 213,000 contigs equivalent to 80% of the silkworm genome have been generated. These contigs have been evaluated by alignment of about 11,000 Bombyx non-redundant ESTs. Almost 90% of the ESTs were identified in the whole genome sequence data.

Life cycle

The life cycle of Bombyx mori demonstrates the most advanced form of metamorphosis. Termed holometabolous, the serial progressions of four distinct stages of development complete one generation of the species—ova, larva, pupa and imago (adult). The number of generations per year or season depends on the voltinism of the silkworm strain and variables including temperature. Voltinism is when some members of a species enter a hibernation-like period of diapause, while others do not. Under natural conditions, silkworm strains producing one generation per year are univoltine. Silkworm larvae have a strong appetite, they eat mulberry leaves day and night. Thus, they grow very fast. When the color of their heads turns darker, it means that it is time for them to moult. After they moult about four times, their bodies turn slightly yellow and their skin becomes tighter, which means they are going to enter an apparently resting state (the pupa or chrysalis), during which they transform themselves into moths. Before becoming a pupa, the silkworm encloses itself in a cocoon, for protection during the vulnerable, almost motionless pupal state. The silkworm is so called because it spins its cocoon from raw silk produced in its salivary glands. The adult phase (the moth) has been bred for silk production and cannot fly. It is also called the silkmoth. They have a wingspan of 5cm and a white hairy body.

Economic importance

Silk is a natural protein fibre that can be woven into textiles. It is obtained from the cocoon of silkworm larvae reared in captivity (sericulture). The cocoon is made of a single continuous thread of raw silk from 300 to 900 meters long. The fibres are very fine and lustrous, about 10 nanometers in diameter. About 4,000 to 6,000 cocoons are required to make one kilogram of silk.

Links

http://www.sericulum.com/

http://www.ab.a.u-tokyo.ac.jp/silkbase/

http://www.nises.affrc.go.jp/sgp/BombMap.htm

http://kaikoblast.dna.affrc.go.jp/

http://silkworm.genomics.org.cn/

http://www.cdfd.org.in/silksatdb/

Drosophila melanogaster

Chromosome number : 2n=8

Genome

Life cycle

The developmental period for Drosophila melanogaster varies with temperature, as all cold-blooded species. The shortest development time (egg to adult), 7 days, is achieved at 28 °C. Development times increase at higher temperatures (30 °C, 11 days) due to heat stress. At 25 °C it takes 8.5 days, at 18 °C it takes 19 days and at 12 °C it takes over 50 days. Females lay some 400 eggs (embryos), about five at a time, into rotting fruit or other organic material. The eggs, which are about 0.5 millimetres long, hatch after 12-15 h (at 25 °C). The resulting 1st-instar larvae grow for about 4 days (at 25 °C) while molting twice (into 2nd- and 3rd-instar larvae), at about 24 and 48 h after eclosion. During this time, they feed on the microorganisms that decompose the fruit, as well as on the sugar of the fruit themselves. Then the larvae encapsulate in the puparium and undergo a four-day-long metamorphosis (at 25 °C), after which the adults eclose (emerge).

Economic importance

Drosophila melanogaster is the most studied organism in biological research, particularly in genetics and developmental biology. There are several reasons:

• It is small and easy to grow in the laboratory
• It has a short generation time (about 2 weeks) and high productivity (females can lay 500 eggs in 10 days)
• The mature larvae show giant chromosomes in the salivary glands called polytene chromosomes - "puffs" indicate regions of transcription and hence gene activity.
• It has only 4 pairs of chromosomes: 3 autosomal, and 1 sex.
• Males do not show recombination, facilitating genetic studies.
• Genetic transformation techniques have been available since 1987.

Links

http://www.flybase.org/

http://www.fruitfly.org/

http://www.dhgp.org/

http://genome.ucsc.edu/cgi-bin/hgGateway?org=D.+melanogaster&db=0

http://www.flymine.org/

http://www.ebi.ac.uk/integr8/ClustrAnalysisPage.do?orgProteomeID=17

http://www.ebi.ac.uk/integr8/InterproAnalysisPage.do?orgProteomeID=17

http://www.flytf.org/

http://www.mcgill.ca/Biology/labs/MDGP/home.html

http://bioinformatica.uab.es/dpdb/

http://flysnp.imp.univie.ac.at/

http://www.flybase.org/allied-data/resources.html

Anopheles gambiae

Chromosome number : 2n=6

Genome

The total length of scaffold sequence in the AgamP3 genome assembly is 264 Mbp of which 87% has been assigned to and ordered on chromosomes. Chromosome arms 2L, 2R, 3L, 3R, and X are represented by 12, 23, 22, 10, and 13 large scaffolds respectively. Two 'artificial chromosomes' have been made with scaffolds concatenated together in size order: 'Y_unplaced' with 55 small scaffolds assigned to the Y chromosome, and 'UNKN' with the remaining 8029 unplaced scaffolds.

Life cycle

Anopheles goes through four stages in their life cycle: egg, larva, pupa, and adult. The first three stages are aquatic and last 5-14 days, depending on the species and the ambient temperature. The adult stage is when the female Anopheles mosquito acts as malaria vector. The adult females can live up to a month (or more in captivity) but most probably do not live more than 1-2 weeks in nature

Economic importance

Anopheles gambiae is a transmission vector of malarial parasite Plasmodium, which infects about 350-500 million people and approximately 1.3 - 3 million deaths annually, mainly in the tropics. The death rate is expected to double in the next 20 years. The exact statistics are unknown because many cases occur in rural areas where people do not have access to hospitals and/or the means to afford health care. Consequently, many cases are undocumented. Children under the age of five and pregnant women are the most vulnerable to the severe forms of malaria.

Links

http://www.anobase.org/

http://www.anobase.org/AnoGenome.html

http://www.anobase.org/cgi-bin/microsat.pl

http://mosquito.colostate.edu/tikiwiki/tiki-index.php

http://www.tigr.org/tigr-scripts/tgi/T_index.cgi?species=mosquito

http://www.ent.iastate.edu/mailinglist/mosquito-l/

http://139.91.171.128/

http://www.ensembl.org/Anopheles_gambiae/index.html

Apis mellifera

Chromosome number : 2n=32

Genome

Honeybee sequencing (7.5 X) was carried out is from the DNA isolated from drones of strain DH4. The genome is being sequenced using a combined whole genome shotgun (WGS) and BAC clone approach. The BAC clone sequence is produced following a pooled-array strategy. The total length of all contigs is 231 Mb. When the gaps between contigs in scaffolds are included, the total span of the assembly is 235 Mb. About 99% of the STS markers and 98% of the EST sequences and 96% of the cDNAs are represented in the assembly. Thus about 79% (186 Mb) of the genome is placed on chromosomes. Moderately repetitive sequences were assembled separately and placed using mate pair information and merged with sequence contigs. Highly repeated sequences, low coverage sequences, and contigs with length less than 1 kb are omitted from the assembly and are available as separate data sets on the FTP site.

Life cycle

A colony of honeybees at the height of the summer contains <50,000 bees. There is one queen (female) capable of laying <2,000 eggs per day, several hundred drones (males), and workers (sterile females). Both the workers and the queen develop from fertilised eggs (egg + sperm) and have 32 chromosomes. The queen is reared in a queen cell and receives a richer and more plentiful diet (royal jelly or brood food). The workers are all potential queens - it is the feeding that makes the difference (workers have rudimentary ovaries and may become laying workers producing drones). The drones develop from unfertilised eggs and have 16 chromosomes. A drone has a mother but does not have a father - but he does have a grandmother & a grandfather!

Economic importance

The honeybee is important in the agricultural community as a producer of honey and as a facilitator of pollination. It is a model organism for studying the following human health issues: immunity, allergic reaction, antibiotic resistance, development, mental health, longevity and diseases of the X chromosome. In addition, biologists are interested in the honey bee's social instincts and behavioral traits.

Links

http://www.bbka.org.uk/articles/life_cycle_apis_mellifera.php

http://www.genome.jp/kegg-bin/show_organism?menu_type=pathway_maps&org=dame

http://www.apis-mellifera-mellifera.de/

http://pat.sdsc.edu/perl/browser.pl?tax=Apis%20mellifera

http://racerx00.tamu.edu/bee_resources.html

http://racerx00.tamu.edu/cgi-bin/cmap/viewer

Tribolium castaneum

Chromosome number : 2n=20

Genome

The beetle genome (200 Mb) has been sequenced to 7 X coverage using a whole genome shotgun approach and assembled using the HGSC's assembly engine, Atlas. Approximately 70% of the genome sequence has been mapped to chromosomes, allowing the creation of linearized chromosome sequence files.

Life cycle

Range of temperature: 22 - 40°C; optimal RH: 75% ; eggs laid: up to 500 ; life cycle: 20 days under optimum conditions. Although small, about a quarter of an inch long, the adults are long-lived and may live for more than three years. The red flour beetle may fly, especially before a storm. Eggs, larvae, and pupae are found in similar environments. The eggs are white, microscopic and often have bits of flour stuck to their surface. The slender larvae are creamy yellow to light brown in color. They have two dark pointed projections on the last body segment.

Economic importance

Tribolium castaneum, a common pest that is also a genetic model for the Coleoptera. Red flour beetles attack stored grain products such as flour, cereals, meal, crackers, beans, spices, pasta, cake mix, dried pet food, dried flowers, chocolate, nuts, seeds, and even dried museum specimens. These beetles have chewing mouthparts, but do not bite or sting. The red flour beetle may elicit an allergic response, but is not known to spread disease and does not feed on or damage the structure of a home or furniture. These beetles are the most important pests of stored products in the home and grocery stores. Tribolium is also one of the most sophisticated genetic model organisms among all higher eukaryotes. As a member of the most primitive order of holometabolous insects, the Coleoptera, it is in a key phylogenetic position to inform us about the genetic innovations that accompanied the evolution of higher forms with more complex development. Coleoptera is the largest and most species diverse of all eukaryotic orders and Tribolium offers the only genetic model for the profusion of medically and economically important species therein. Analysis of the Tribolium genome will facilitate the discovery of new pharmaceuticals and antibiotics. In addition, it will lead to a better understanding of resistance mechanisms and improved specificity and efficacy of insecticides and biological agents to control crop pests and disease vectors.

Links

http://www.bioinformatics.ksu.edu/BeetleBase/

http://www.ksu.edu/tribolium/

http://www.biologie.uni-erlangen.de/entwbio/TriboliumNet/index.html

http://creatures.ifas.ufl.edu/urban/beetles/red_flour_beetle.htm

http://bru.gmprc.ksu.edu/proj/tribolium/

http://www.ento.csiro.au/aicn/name_s/b_4116.htm