Young bolls may be shed owing to the mechanical action of stainer puncturing, apart from the introduction of any specific internal boll disease. One puncture is sufficient to obtain this effect.

Unless the carpel wall is pierced, no injury to the boll from insect attack results, and it is highly probable that the piercing of the carpel wall is essential for the introduction of internal boll disease.

Internal proliferation does not take place unless the carpel wall is pierced, and is not an essential factor in the shedding of young bolls, but rather an indication of injury from an external source.

Puncturing by stainers of the buds and flowers, before the flower petals have fallen off, may cause the shedding of the boll and the introduction of internal boll disease.

The surest superficial diagnosis of stainer injury to bolls, as compared with other insect injuries, is the finding of a bead of moisture exuding from the single minute orifice, in the case of a fresh puncture, and of a minute canal in the centre of the corked area of an injury some days old. The regularity of the rim of the corked area is a strong indication of stainer injury, the periphery of the corked area produced by the nibbling of young Lepidopterous larvae being irregular, owing to the action of the mandibles.