Stridulation and associated behaviour in certain orthoptera. 2. Stridulation of females and their behaviour with males

1. The stridulation of females and their behaviour in relation to males was studied comparatively in the following species of Truxalinae: Stenobothrus lineatus (Panzer); Omocestus viridulus (Linnaeus); Chorthippus parallelus (Zetterstedt); and Chorthippus brunneus (Thunberg) (= C. bicolor Charp.).

2. Descriptions of the “typical behaviour” of females in response to normal song are given. This behaviour is similar in all species and consists of three phases: response stridulation, orientation towards and locomotion to the male. Arrived near the male, the female stridulates in response to mate song; the male, on noticing the female, sings the courtship song, engages the genitalia and copulation ensues. Females showing such typical behaviour are said to be in the “responsive state”.

3. This responsive state in females of the four species appears at maturation, is inhibited for periods up to 24 hours prior to oviposition, is regained shortly afterwards and is lost some days prior to death. Complete copulation involving the transfer of a spermatophore also inhibits the responsive state in the females; if the latter are isolated after copulation, they regain their responsiveness in a period of from 6–20 days dependent on the species. This recovery is delayed or prevented if the females are kept after copulation with males or within the sound of male normal song.

4. The responsive state is characterised in most females of all four species by the emission of stridulation in response to male normal song. In all cases, the movements of the hind femora of a female emitting this stridulation are very similar to those of a male of the same species singing the normal song. In the case of S. lineatus, O. viridulus and C. brunneus, audible sounds are emitted by the females, which in the case of the latter two species show marked affinity to male normal song. Physical analyses of these sounds are presented. Females of C. parallelus, being brachypterous, emit no sound while making stridulation movements of the hind femora.

5. It is postulated that the discrimination mechanism responsible for distinguishing between various specific songs is closely linked to the inherited motor mechanism which causes typical stridulation in both sexes. It is further suggested that the basic behaviour reactions of males and females to male normal song are the same, consisting of stridulation response movements, orientation and locomotion towards the male. Normally in the field, the last two phases are suppressed in males, the whole sequence in females. Isolation restores full typical behaviour in both males and females and, in the latter, stridulation is always an indicator of the return of the responsive state.

6. The observations are used to construct a possible picture of events in the field concerned with courtship and mating in the present species.