The colour of the green and brown forms of Silobion avenae result from qualitative and quantitative differences in their carotene pigments. The green form contained mainly a-carotene (bicyclic), and the brown form mainly y-carotene (monocyclic), lycopene, torulene and 3', 4'-didehydrolycopene (acyclic). The total carotene content of the brown form was approximately three times higher than the green form. The striking pink colour of male Metopolophium dirhodum was the result of qualitative differences in carotenes present in the green vir'ginoparae of this species. To investigate the possibility that *brown clones had a selective advantage over green clones at long " daylengths, six clones of S. avenae (three green and three dark), were reared on artificial diet, at photoperiods of either 8,16 or 24 h. The fecundity of five of the clones was highest at 16 h and lowest at 8h. One of the brown clones had its highest fecundity at 24 h and lowest at 8h. These results do not support the hypothesis that brown clones have a selective advantage at long daylengths. When a green and a brown clone were exposed to UV light (58 tmol m-2), the brown clone suffered the least mortality and had a significantly lower reduction in fecundity. This result suggests that at high light intensities brown clones have a selective advantage over green clones. Another possible source of selective advantage investigated was the number of bacteriacytes individuals of the above clones possessed. This was estimated by histological examination and no significant difference was foundThe carotenes of S. avenae are not derived from an exogenous source, as three clones were reared on a diet lacking carotenoids for up to three generations, with no loss of pigmentation. Adding chlorotetracycline to the diet did not inhibit the production of carotenes. This result suggests that the symbionts are not synthesising the carotenes. The colour of the offspring of virginoparae, reared on artificial diet at a number of different daylengths, was not affected. When sexual morphs were induced, the oviparae of the brown forms were green. Individuals of an insecticide resistant strain of Myzus persicae, whose symbionts were disrupted by feeding them on a diet containing antibiotic did not show a reduction in the base level of esterase E4 activity, the enzyme conferring resistance in this species. This demonstrates that the bacteriasome is probably not the major site of synthesis of this enzyme
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:294089 |
| Date | January 1991 |
| Creators | Jenkins, Rhodri Lloyd |
| Publisher | University of East Anglia |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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