The general biology and phenology of swarming in the East African tettigoniidRuspolia differens(Serville) (Orthoptera)

Summary (1) The taxonomic status of Homorocoryphus nitidulus vicinus Walker is restated following the revision of this genus (Bailey, 1975).(2) R. differens is sympatric with at least two other species in the area studied in this work, notably R. flavovirens and R. fuscopunctata.(3) Courtship is primarily based on song. The role of the song in courtship and swarm formation is discussed.(4) Oviposition is in the haulms of grasses and it is considered that the oviposition site of this species has a direct bearing on the synchrony of development and eventual synchrony of swarming. It is suggested that the development of the grass is linked with the development of R. differens. (5) The development of R. differens from anatrepsis is discussed in relation to the availability of water and the expected times of the ‘first rain’ and the emergence of the first instar. Eclosion tends to be synchronous.(6) The relationship between the fat reserves of R. differens and its total flight activity is discussed; comparison is made with the non-swarming sympatric species R. flavovirens. The state of the mitochondrial christae of the flight muscles in relation to swarming and age of the insect is considered.(7) R. differens exhibits six colour forms of which green and brown are the most common. Females have a higher incidence of green than males.(8) The sex ratio within the swarm is discussed and results of sampling under varying conditions are compared with those of previous workers.(9) The parasites of R. differens consist mainly of a tachinid fly. Comments are made on a species of mite infecting the sympatric species R. flavovirens.(10) Predators of R. differens are mainly birds; a list is given of birds observed eating this insect. Mammals including man use R. differens as a food source; a list of observed mammals is also given.(11) The pest status of R. differens based mainly on the observations of previous workers is summarized.(12) A detailed account is presented of the behaviour of swarms in both rural and urban environments. It is stated that the most important evidence for the total phenology of swarming would be from direct observations in a rural situation. Analyses of two principal swarming periods in 1961–1962 and 1964 are given and an attempt is made to correlate the various sightings of these swarms throughout East Africa.(13) Details are provided of the sequential and possibly concurrent diversion of numerous swarms to the lights of Kampala. Such accumulation of small swarms could lead by a snowball effect to the build-up of massive swarms. The subsequent effect of predators is discussed.(14) The seasonality of swarming is presented and discussed with relation to seasonal rainfall, changes in lake levels and changes in grassland and diet. It is concluded that swarming is governed both by favourable rainfall and unfavourable drought, operating through changes in grasslands.(15) The phenology of swarming in R. differens is finally discussed within the frame of general theory.