The probing behavior and feeding activity of green peach aphid, Myzus persicae Sulzer, on Bacillus thuringiensis ssp. tenebrionis- transgenic potatoes, insecticide treated potatoes, and host plants with different preference were electronically monitored. I found that first, transgenic potatoes had no effect on green peach aphid probing suggesting that transmission of green peach aphid-borne viruses would not be affected. Second, the probing behavior of green peach aphid was not modified by the insecticides, aldicarb, Admire, and Di-syston. However, the postfeeding behavior of aphids was different over time and with insecticides, which might have an influence on virus transmission in the field. Third, the probing behavior of green peach aphid on host plants with different preference varied. Aphids probed more when they moved from a higher-preference host plant (radish) to a lower preference host plant (potato). In addition, the settling rate was low when aphids were moved from higher to lower preference host plants. This difference might affect virus transmission in the field. Vector efficiency, relationship of virus transmission between vector and host plants, and vector control strategies are discussed. In addition, the probing behavior of two mosquito species, Aedes aegypti and Anopheles stephensi, on mice was recorded electronically to examine waveform patterns and to quantify sporozoite output. My studies indicated that sporozoite output of malaria-infected mosquitoes was not detected by using the electronic monitoring system. The relationship between waveform patterns and penetration activities of mosquitoes needs clarification before further studies can be conducted. / Graduation date: 1994