178
V. G. DETHIER
relationship between concentration and response. Wharton et al.
(1954a, b) prepared a series of dilutions of the attractant extracted from
paper on which females of Periplaneta americana had lived for about
one week. The responses of samples of males to different concentrations of this substance absorbed on paper were observed. As Roth and
Willis had shown, males respond by a sudden alerting movement, movement of the antennae, and finally by actively searching for the source of
odor with fluttering of the wings. It was clearly demonstrated that the
percentage of response of males is proportional to the logarithm of concentration over a wide range. In this respect the response to the sex
attractant is the same as the responses of other insects to various attractants and repellents (Dethier and Chadwick, 1948; Dethier, 1953a).
Furthermore, the median threshold of response differs, depending on
whether the various concentrations of stimulus are offered in an ascending or descending order of concentration. In general, the median threshold is higher for ascending series than for descending series. This result,
plus demonstration of a decline in response with repeated stimulation
with a particular concentration, reveals the existence of adaptation of the
classical type. As far as the present discussion is concerned, the results
of Wharton et al. show clearly that the physiological action of the cockroach sex attractant is such as to place it in the same category with other
kinds of chemical stimuli which have been extensively studied on the
physiological rather than on a strictly behavioral basis.
VII. CONCLUSION
The four patterns of behavior which have been discussed, namely, hostfinding and discrimination by parasitoid insects, trail-following, orientation to odors by flying insects, and courtship, have been shown to depend
for their successful consummation upon a variety of stimuli of which the
chemical ones are of critical importance. The examples chosen illustrate
the roles of chemicals as directing stimuli and as stimuli which release
innate behavior patterns. Those stimuli which we usually think of as
odors may act in both capacities, while those we are accustomed to
call tastes or contact chemical stimuli act principally as releasers. Chemical cues are no less important than are visual cues for microsmatic animals. Like visual cues they may exert a predominating influence but
nontheless sum with other modalities of stimulation and may substitute
for or be substituted by other stimuli. Much of the confused understanding of various complicated insect behavior patterns can be attributed directly to a failure to appreciate the law of heterogeneous
summation. Elucidation has come also with a more subtle understanding of the potentialities and limitations of chemoreceptors. Thus has
V. G. DETHIER
relationship between concentration and response. Wharton et al.
(1954a, b) prepared a series of dilutions of the attractant extracted from
paper on which females of Periplaneta americana had lived for about
one week. The responses of samples of males to different concentrations of this substance absorbed on paper were observed. As Roth and
Willis had shown, males respond by a sudden alerting movement, movement of the antennae, and finally by actively searching for the source of
odor with fluttering of the wings. It was clearly demonstrated that the
percentage of response of males is proportional to the logarithm of concentration over a wide range. In this respect the response to the sex
attractant is the same as the responses of other insects to various attractants and repellents (Dethier and Chadwick, 1948; Dethier, 1953a).
Furthermore, the median threshold of response differs, depending on
whether the various concentrations of stimulus are offered in an ascending or descending order of concentration. In general, the median threshold is higher for ascending series than for descending series. This result,
plus demonstration of a decline in response with repeated stimulation
with a particular concentration, reveals the existence of adaptation of the
classical type. As far as the present discussion is concerned, the results
of Wharton et al. show clearly that the physiological action of the cockroach sex attractant is such as to place it in the same category with other
kinds of chemical stimuli which have been extensively studied on the
physiological rather than on a strictly behavioral basis.
VII. CONCLUSION
The four patterns of behavior which have been discussed, namely, hostfinding and discrimination by parasitoid insects, trail-following, orientation to odors by flying insects, and courtship, have been shown to depend
for their successful consummation upon a variety of stimuli of which the
chemical ones are of critical importance. The examples chosen illustrate
the roles of chemicals as directing stimuli and as stimuli which release
innate behavior patterns. Those stimuli which we usually think of as
odors may act in both capacities, while those we are accustomed to
call tastes or contact chemical stimuli act principally as releasers. Chemical cues are no less important than are visual cues for microsmatic animals. Like visual cues they may exert a predominating influence but
nontheless sum with other modalities of stimulation and may substitute
for or be substituted by other stimuli. Much of the confused understanding of various complicated insect behavior patterns can be attributed directly to a failure to appreciate the law of heterogeneous
summation. Elucidation has come also with a more subtle understanding of the potentialities and limitations of chemoreceptors. Thus has