Abstract: Eleven new synthetic polyacetylenes were screened for their biological activity to the 4th instar larvae of the mosquito Culex quinquefasciatus. The toxicities of some compounds to the tested insects were found to be enhanced greatly by irradiation with near-UV. Compound 5 (1-phenyl4(3,4methylenedioxy)phenyl-diacetylene) is an effective photosensitizer,of which LC_{50+UV-A (in the presence of UV-A) and LC50-UV-A(in the absence of UV-A) to the larvae were 0.35 μg/mL and 8.89 μg/mL respectively.The ratio of photoactivity ［(LC50-UV-A)/(LC50+UV-A)］ was 25.65. The results in simulated field experiment showed the phototoxicity of compound 5 also was enhanced greatly to the tested larvae by sunlight. The mortality of presence and absence of sunlight were 81.63 and 11.40 percent respectively. The result of preliminary experiment by adding different kinds of antioxidants showed the compound 5 belongs to the type of yielding superoxygen radical in organism and it differs from α-terthienyl (α-T) in the mechanism of photodynamic action. The analysis of structure-bioactivity shows that diacetylene of biphenyl-containing derivatives has higher activity in photoxicity than diacetylene of bialkyl substitute. Different substitutes on phenyl also affect its effect,the order in activity is methylene dioxy>methoxy>o-nitro>m-nitro>methyl ester.}

Key words: polyacethlenes, Culex quinquefasciatus, phototoxicity