Wax moth larvae (Galleria mellonella L.) and yellow mealworm larvae (Tenebrio molitor L.) were reared on five different diets respectively, to determine which diet resulted in the highest increase in insect larval weight. Wax moth eggs were placed on each diet and larvae that developed therefrom were weighed after 51 days. A diet containing 118 g wheat flour, 206 g wheat bran, 118 g milk powder, 88 g brewer's yeast, 24 g wax powder, 175 ml honey and 175 ml glycerol, produced the heaviest larvae, with an average weight of 0.19 g per larva. Mealworms were weighed 62 days after adult beetles were placed on the various diets. The heaviest larvae were produced on a diet consisting of wheat bran only, with each larva weighing, on average, 0.0154 g. Nematode production of Heterorhabditis zealandica and H. bacteriophora using wax moth, mealworm, codling moth (Cydia pomonella) and false codling moth (Thaumatotibia leucotreta) larvae were determined, as well as was the correlation between the weight of the host larvae and that of the nematode progeny produced. Wax moth larvae produced the highest number of H. zealandica and H. bacteriophora per g of host. The mean number of H. zealandica and H. bacteriophora infective juveniles produced were 1 459 205 and 1 898 512, respectively, per g of host. The mean number of H. zealandica produced per g of codling moth and false codling moth larvae was 57 582 and 192 867, respectively. Lower mean numbers were produced for codling moth and false codling moth larvae when using H. bacteriophora, with 39 653 and 97 652 nematodes produced per g of the respective hosts. A significant positive linear relationship existed between weight of wax moth larvae and that of mealworm and the number of nematodes produced. Using frozen hosts of wax moth larvae and mealworm, comparable reproduction of nematodes was only found with mealworm.