In the British Solomon Islands Protectorate, the incidence of the immature nutfall of coconuts that is caused by species of Amblypelta depends upon the distribution of (1) the species that are concerned, which determines on what islands nutfall occurs, and (2) certain species of ants, which affects the local distribution of nutfall on those islands. A. cocophaga China is the most important member of the genus as regards responsibility for nutfall; A. cristobalensis Brown and to a less extent A. costalis Van Duzee also frequent the coconut palm and cause nutfall, but not on a serious scale; A. gallegonis Lever rarely, if ever, attacks coconut.

The current view that Oecophylla smaragdina (F.) protects coconuts against Amblypelta, and that Pheidole megacephala (F.) and Iridomyrmex myrmecodiae Emery give little or no protection, is accepted, but evidence is brought forward showing that Iridomyrmex appears to give some protection against A. cristobalensis on San Cristobal. Most attention has been given to a fourth species of ant, Anoplolepis longipes (Jerd.), the relation of which to nutfall has hitherto been in some doubt; evidence from various sources shows that, at least on Guadalcanal and Malaita, it gives nearly, if not quite, as much protection against Amblypelta as Oecophylla does.

A method based on crop estimation is used to give some indication of the losses due to nutfall in the European plantations that have been surveyed. The accuracy of the method is discussed in an Appendix. Varying numbers of nuts survive to maturity in nutfall areas, depending on the intensity of attack. In addition to the loss caused by the failure of nuts to survive to maturity, Amblypelta attack causes further losses by reducing the amount of copra obtainable from surviving nuts, and by rendering plantations where the attack is sufficiently severe unprofitable to work, so that they become, in effect, a total loss, even though a proportion of the nuts may survive attack.

An attempt is made to evaluate and compare the fraction of the crop lost on some of the principal islands, but it is impossible to give an even approximately accurate figure for the losses due to nutfall in the islands as a whole, because essential data, comprising the planted acreage of each plantation and island, and, except for a very few plantations, details of annual production figures over a period of years, are often lacking; also, limited time has made it impossible to survey many of the plantations in sufficient detail for an accurate assessment of nutfall.

A list is given of the species of ants recorded from coconut plantations during the present work.