Drosophila melanogaster Linnaeus was reared for single generation in the laboratory on a simple diet of 13gm yeast, 250gm milk, 20gm cellulose tissue and 1L water.
Keywords: Drosophila melanogaster, laboratory rearing, developmental stages, artificial diet
Drosophila melanogaster is commonly known as fruit fly since it's always found near unripe and rotted fruit. The fly inspired its genus name from the Latin word means "dew loving". This genus could b easily identified by presence of black characteristic hairs over their compound eye. This smallish fly has been paid attention since early 90th in many scientific investigations concerning behavioral and genetic studies. Thomas Hunt Morgan was the first and outstanding biologist studying Drosophila early in the 1900's. He was the first to discover sex linked genes and genetic assortment, segregation, and recombination, which put the fly as a model of genetic research. And cause of its smallish size, ease of culture and short generation time, geneticists have been using the fly ever since. Drosophila sp. is one of the few organisms whose entire genome is known and many of its genes have been identified and used in many other scientific researches. The very fast development enables this organism to develop from eggs to adult stage during 9-12 days in 25°C. Usually the fly spends five days in the egg and larval stages and four days in the pupal stage. The adult may live for several weeks. Drosophila sp. should not be reared in high temperatures (e.g. above 30°C) that will result in sterilization or death of the flies or to low temperatures (e.g. below 10°C) that also will result in a prolonged life cycle, maybe 57 days, and eventually reduced viability. Their body is usually pale yellow to reddish brown to black in color, with large, red eyes and oval-shaped wings, maybe sometimes it has some distinct black patterns. Also their wing venation is peculiar to the entire family. The body form could be mutated due to culturing conditions, which produces offspring with body characters quietly different from parents. For instance, higher temperatures might alter the phenotype of the eye and body color, or may change the wing shape and size.
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The entire genus of Drosophila sp. contains more than 15000 species and is very diverse in appearance, behavior, and breeding habitat (Gerhard Bächli, 1999-2006). Drosophila sp. found all over the world, but most of their species are predominant in the tropical regions. They are multivoltine species, and the northern species can hibernate. They breed in various kinds of decaying plants and fungal materials. The larvae of some species can also feed on fresh fruit and can sometimes be a pest ( Mark Hoddle). Some other few species maybe switched in order to be parasites or predators. Most of their species are attracted to bait of fermented fruits or any other fermented odor, but little of them are not attracted to any kind of baits. Males usually congregate at patches of suitable breeding habitats to compete for females. Several Drosophila species, such as D. melanogaster, are closely associated with humans; thereby they are called as domestic species. But most of Drosophila sp. have been accidentally to new areas due to anthropogenic activities and fruit transportation (Vilela, 1999; Van der Linde et al., 2006; Castrezana, 2007).
The fruit fly varies in their reproductive capacity. D. melanogaster, breeds in rare, limited resources, have ovaries that mature 10-20 eggs at a time, so that they can be laid together on one site. Others, those breed in more-abundant but less nutritious substrates, may only lay one egg per day. Only the adult stage feeds on vegetable matters, whereas larvae, the feeding immature stage, feed on yeast and microorganisms present on decaying breeding substrate. Their developmental time vary according to species. It is varied from 7 - more than 60 days. Also, it may vary within the same species depending on the environmental factors such as temperature, breeding substrate, and crowding.
In this study, D. melanogaster collected and cultured under laboratory conditions, using artificial substrates to investigate different immature stages and the mean developmental time for each stage.
Materials and Methods
1. Collecting and Culturing Media
Diet mixture of yeast, milk and cellulose was put in plastic bottle. The bottle was cut into two halves, the nick top half, which put inverted on the bottom half. The media recipe was devised as below:
Cellulose tissue 20gm
This media is blended and placed in plastic collecting bottles containing crumpled paper toweling to prevent flies drowning. The media was stored at 30o for 2-3 days until fermented (Krivshenko 1963), then put outdoor to collect adult. The collecting bottle was checked twice daily (day and night). The collecting bottle left for three days to collect as much as possible of D. melanogaster flies. The collected individuals transferred to culturing bottle under the laboratory conditions (25°±5°C) at plant protection department, Food and Agriculture Sciences College, King Saud University, for conducting the experiment.
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Flies oviposited in the diet. After 24 hrs, adult flies were removed from the bottles using their positive phototactic response and maintained in 20x20cm cage fitted with a sleeve and fed with 2.5 % sugar solution through cotton wicks. Small 50ml vials with culturing media were used for maintaining small larvae individually and avoid crowding. Number of larval developmental stages and time taken until pupal stage were recorded.
Study area and period
The study was conducted for 30 days (December, 2010) starting culturing step. Three collecting bottles were used in three selected sites for adult D. melanogaster collection; the educational farm of Food and Agriculture Sciences College, referred as site A, the main building of the College, referred as site B, and the students housing at King Saud University, referred as site C.
Results and Discussion
Total of 23 adults were collected in the three collecting bottles. Both Sites A and C were negative for adult fly. Eggs laid couldn't be observed since adult females put them in tiny cracks of the culturing media. 301 larvae have been recorded within 24hrs. The mean developmental time for larvae was 7 days to pupation. By the eighth day, all larvae pupate (Fig. 1).
Only single adult failed to emerge by the eleventh day. No adult were emerged until the end of month, which means that successful adult emergence took almost 22 days.
The rapid development of early immature stages proved favorable conditions for larval development that was not quietly enough for the pupal stage development into adult emergence.
The developmental period for fruit fly varies mainly with temperature, as with many ectothermic species. The shortest recorded development time (egg to adult), 7 days, is achieved at 28°C (Ashburner and Thompson 1978, Ashburner et al., 2005). Development time increases at higher temperatures (11 days at 30°C) cause of heat stress. The ideal development time at 25°C is supposed to be 8.5 days as Ashburner and Thompson (1978), Ashburner et al., (2005), and Chiang and Hodson (1950) reported in previous investigations. Nevertheless, the findings of the current study showed longer development time especially for late immature stage (pupa). This might be explained, as the temperature of the laboratory was not optimum (<25°C) to cause successful adult emergence. This finding goes along with Ashburner and Thompson (1978) and Ashburner et al., (2005) that's the development time at 18 °C takes 19 days, and at 12 °C it takes over 50 days.
Crowding has no effect on development time since larvae were separated individually in culturing media. More over, under crowding increases the development time (Chiang and Hodson 1950), while the emerging flies are smaller (Chiang and Hodson 1950, Bakker 1961).
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