The relation between shoot density and attack hi infestations of barley by a shoot fly larva.
The following is based largely on the author's summary of this account of investigations in Kenya. The percentage of barley shoots attacked by larvae of Hylemya arambourgi Séguy [cf. RAE A 53 264] was found to vary between samples taken at one time from replicates of plants grown from unprotected seeds and seeds protected by a dieldrin dressing. The number of shoots on a plant did not affect the level of infestation, but shoots of different lengths varied in susceptibility to attack, those 13-17 cm long being the most susceptible. Variation in the numbers of shoots of different lengths between samples is shown to be closely related to the number of attacked shoots, especially in plants protected by insecticide treatments. In unprotected plants, the pattern of shoot production is disrupted by a traumatic response to attack, which, it is suggested, would result in different growth rates in shoots, leading to a partial breakdown of the relation between length and susceptibility. It is suggested that failure to appreciate this variation could lead to difficulties in interpreting series of experiments on control and that the variable shoot production would lead to a poor correlation between yield and attack.