Westigard et a. (1975) found differential mortality in eggs and first-instar larvae in the three pear varieties that was related to antibiosis and the degree of lignification and stone-cell formation in the fruit. Nel (1985) described that in apricot in South Africa only one generation developed in one season, whereas two generations developed on apple and pear. In addition to the food supply, apple density in relation to moth density is an important factor regulating voltinism in the codling moth (Riedl, 1983). Apple is the preferred host of the codling moth. This is the reason that the codling moth occurs where apples are grown throughout the temperate regions of the world, except in Japan and on the mainland of Asia (Chapman and Lienk, 1971). The apple population displayed ovipositional preference for apple while the walnut and plum populations preferred walnut (Riedl, 1983). Preference of a certain host was genetically based but was also influenced by host conditioning. Phillips and Barnes (1975; cited by Riedl, 1983) determined that the developmental heat requirement of the plum race was lower than in the other two races.
 

To summarize the main point, the quality of the food plant influences development and the preimaginal mortality of codling moth larvae. Apple is the preferred host of the codling moth. This is the reason that the codling moth occurs where apples are grown throughout the temperate regions of the world. The food supply, in relation to moth density, is an important factor regulating voltinism in the codling moth.