| The mechanism of photosensitivity and phototaxis was studied by extracellular electrophysiological record technique on the compound eye of ladybird (Propylaea japonica Thunberg) which is the main natural enemy of moth (Helicoverpa armigera Hubner). The results are the follows.1. The compound eye of ladybird will turn out the ERG responses with the different amplitudes, when the compound eye was stimulated by monochromatic lights which are ultraviolet radiation and most of visible lights with different wavelengths. According to the values of amplitudes, there are three peaks in the spectral sensitivity curve of the compound eye of ladybird. The main peak values are 562nm, 524nm and 460nm which indicate that the photoreceptor of the compound eye of ladybird has three kinds.2. In a certain range of relative intensity, with increasing the relative intensity, the values of ERG of ladybird's compound eye will increase when the compound eye of ladybird is stimulated by white radiation. However, the rate of increasing makes creeping when the relative intensity is certain value. The curve appears near S shape. The curve reveals that the compound eye of ladybird has strong adjustability to light and sunproof ability.3. The sex, the intrinsic diurnal rhythm of ladybird and the time of dark-adapted will have some effects on the values of ERG of ladybird's compound eye. In the same condition, the value of ERG of female ladybird's compound eye is larger than the male's; The value of ERG of ladybird's compound eye in day is smaller than in night;Every ladybird need the different time to make the value of ERG stabilization. Mostof ladybirds need about 2 hours.Ladybird (Propylaea japonica Thunberg) is the main natural enemy in the cotton field. Studying its mechanism of photosensitivity and phototaxis, we can get the scientific theoretics for using lamps to kill pests, can implement IPM well to utilize and protect natural enemy, and maintain environment to balance.
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