CHEMORECEPTION AND THE BEHAVIOR OF INSECTS
173
attempt to ascertain more about the nature of the stimulus and response
involving the legs, Spieth tested the effect of amputation of the foretarsi
on mating in two strains of D. virilis. For example, normal males of the
Texmelucan strain fecundated only homogamic females, whereas males
lacking foretarsi fecundated homogamic just as readily as before and
heterogamic females to the extent of 37%. On the contrary, while normal
males of the Pasadena strain fecundated only homogamic females, the
operated males failed to fecundate heterogamic females but at the same
time failed to fecundate many of the homogamic females. Although the
operation resulted in a loss of the ability to discriminate in the case of
Texmelucan males, it reduced altogether the fecundation in the Pasadena
strain. The last result could be explained by assuming that no appropriate stimuli whatsoever were received, so courtship was terminated.
Results of this sort, i.e., failure of action in the absence of stimuli, are
not uncommon. In feeding, for example, some insects deprived of the
ability to discriminate between different foods tend to become omnivorous, while other species deprived of the stimuli necessary to initiate
feeding cease altogether. Similarly, some ants (Myrmicinae) when deprived of their antennae, by which friends and foes are discriminated,
attack friend and foe alike, while others (Fornicinae) feed and tend
friend and foe alike (Forel, 1928). In any event, the experiments performed by Spieth show conclusively that the foretarsi of the males of
D. virilis receive stimuli which aid in distinguishing strains of females
and in some cases serve also for sex discrimination. It is well known, of
course, that the tarsi of all legs of Drosophila bear chemoreceptors by
means of which the fly can distinguish between sugars and water and
between water and many repellent compounds such as salts, acids, etc.
All of the tarsi bear these receptors. For species-discrimination and for
sex-discrimination apparently only the foretarsi are effective. Several explanations could be offered. The difference in tarsi could be a result of
threshold levels, of a specificity of receptors, or of some mechanical
impediment to tapping effectively with mesothoracic or metathoracic
tarsi. But it is clear that in any event chemoreception is concerned and
is of great importance at this stage in strain and species isolation.
According to Spieth, the reception of specific stimuli is mutual; the
females in some instances apparently can determine who is doing the
tapping. Just how this information is received is unclear. In any event,
the tapping male responds according to the nature of the stimulus
received. If the female is of the correct species, the male now postures.
The complexity of posturing varies from species to species. The female
may either accept or reject the male at this point. Apparently the judgment of the female is made primarily on the basis of sensory informa-
173
attempt to ascertain more about the nature of the stimulus and response
involving the legs, Spieth tested the effect of amputation of the foretarsi
on mating in two strains of D. virilis. For example, normal males of the
Texmelucan strain fecundated only homogamic females, whereas males
lacking foretarsi fecundated homogamic just as readily as before and
heterogamic females to the extent of 37%. On the contrary, while normal
males of the Pasadena strain fecundated only homogamic females, the
operated males failed to fecundate heterogamic females but at the same
time failed to fecundate many of the homogamic females. Although the
operation resulted in a loss of the ability to discriminate in the case of
Texmelucan males, it reduced altogether the fecundation in the Pasadena
strain. The last result could be explained by assuming that no appropriate stimuli whatsoever were received, so courtship was terminated.
Results of this sort, i.e., failure of action in the absence of stimuli, are
not uncommon. In feeding, for example, some insects deprived of the
ability to discriminate between different foods tend to become omnivorous, while other species deprived of the stimuli necessary to initiate
feeding cease altogether. Similarly, some ants (Myrmicinae) when deprived of their antennae, by which friends and foes are discriminated,
attack friend and foe alike, while others (Fornicinae) feed and tend
friend and foe alike (Forel, 1928). In any event, the experiments performed by Spieth show conclusively that the foretarsi of the males of
D. virilis receive stimuli which aid in distinguishing strains of females
and in some cases serve also for sex discrimination. It is well known, of
course, that the tarsi of all legs of Drosophila bear chemoreceptors by
means of which the fly can distinguish between sugars and water and
between water and many repellent compounds such as salts, acids, etc.
All of the tarsi bear these receptors. For species-discrimination and for
sex-discrimination apparently only the foretarsi are effective. Several explanations could be offered. The difference in tarsi could be a result of
threshold levels, of a specificity of receptors, or of some mechanical
impediment to tapping effectively with mesothoracic or metathoracic
tarsi. But it is clear that in any event chemoreception is concerned and
is of great importance at this stage in strain and species isolation.
According to Spieth, the reception of specific stimuli is mutual; the
females in some instances apparently can determine who is doing the
tapping. Just how this information is received is unclear. In any event,
the tapping male responds according to the nature of the stimulus
received. If the female is of the correct species, the male now postures.
The complexity of posturing varies from species to species. The female
may either accept or reject the male at this point. Apparently the judgment of the female is made primarily on the basis of sensory informa-