Endosymbionts bacteria help insects exploit the plant hosts by providing essential nutrients which cannot be taken in from the diet, or contribute to digest and to detoxify the food. For instance, aphids are sucking feeding animals. The fluids have high concentration carbohydrates but lack of nitrogen such as amino acids. To overcome this, aphids cooperate with symbiont Buchnera aphidicola. Buchnera produce essential amino acids for host insects, in return, aphids provide nutrients which are obligatory for Buchnera surviving. This association with in these two species have already existed 150 to 200 millions years.
In the meanwhile, symbiotic bacteria proved to play an important role in insect’s defense behavior, which can help them less being attacked by pathogen and parasitoid. It has been shown that endosymbiont can mediate the host’s thermal tolerance, which easy for them to use to the new hosts.
Symbiont- free aphids, Acyrthosiphon pisum (Hemiptera: Aphididae) are a common species in Europe. They reproduce parthenogenetically during spring and summer in overlapping generations. One generation is completed within 10 days at 20°C regularly. For our experiments, laboratory cultures of A. pisum were established from insects collected in the field in Oxfordshire (southern England). They will be reared on 2-week old bean plants under room temperate and natural sunlight in ecological lab. This plant is also known as Vicia faba, cv., or The Sutton dwarf, or Fabaceae. Under these conditions aphids will reproduce asexually by parthenogenesis so clonal lines can be maintained with no genetic variation within the aphid population. The parasitic wasp, Aphids A.ervi., were purchased from Koppert company. Stocks will be kept under 14°C and 16s of light daily, five offsprings are placed on the two weeks old small pot soybean, 10 days water once, three weeks change new plants. All the aphids clones carried symbiont naturally. H. defensa can be tested with a diagnostic PCR. Buchnera – antibiotic, which has no harm to the aphid’s obligate symbiont, can cure the bacteria and give us symbiont free aphids.
To obtain good quality wasps, wasp’s culture will be generated every 9 days as following: Two big pots with five two weeks old bean plants in each will be used to rear 100 adult aphids. Plants with aphids were settled in an insect rearing cage (BugDorm-42222: L 24.5 x W 24.5 x H 24.5 cm) and kept in the cabinet under 20°C and 24 hours light. Two days will be given to 100 adults to produce offspring. After those adults were removed, in the mean while, 1-3 days old offspring were left on plants in cages. On the next day, six female wasps were collected and released in the cage for parasitoid, which will be removed after 24 hours. It would take 8 to 12 days to get next adult wasp generation. 10% solution of honey water and wet tissue will be provided as essential material for surviving. Only 1-3 days old female wasps can be used for experiment.
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