94 



The heating ramp consisted of a 0.5 min hold at 30°C followed by a 10°C/min ramp 



up to 190°C and a final hold of 2.0 min. The transfer line was initially set to 50°C 

 and ramped immediately at 20°C/min to 200°C and held at the temperature for the 

 remainder of the experiment. A deactivated 1.5 m x 0.10 mm i.d. FSOT column was 

 used to transfer the sample to the ion source of the mass spectrometer. These 

 experiments employed methane (1650 mtorr indicated) as the moderating gas for 

 negative ion CI. The ion source and manifold temperatures were 150°C and 70°C, 

 respectively. The filament emission current was set at 200 nA with 100 eV as the 

 electron energy. The scan time was 0.5 s. The electron multiplier voltage was -900 

 V with the conversion dynode at +5 kV. 



Altering Attraction 



Data were acquired by examining mosquitoes collected over a three minute 

 interval of exposure to sampled compounds. These experiments were conducted at 

 the USDA laboratories. Prior to sampling, seventy-five mosquitoes are acclimated 

 in the holding tank for approximately one hour. Once a sample was tested, a new 

 batch of mosquitoes were allowed to acclimate in the tank. The samples examined 

 were methanolic lactic acid solutions. A stock solution of 12 ^.g/tiL L-lactic acid in 

 methanol was prepared. The stock solution was split into 20 mL aliquots and spiked 

 with either acid or base, leaving one solution unspiked as the control. The pH was 

 measured relative to a glass electrode to give an approximate value of the acid or 

 base content of the solution. The pH measurements, from methanolic solutions, do 



