Effects of nitidulid beetles on pollination and fruit set of Annona spp. hybrids

Self, wind and insect pollination mechanisms were evaluated in Annona spp. hybrids in subtropical Australia (Lat. 27°S). Natural fruit set increased linearly (r = 0.90, P < 0.01) with increasing numbers of nitidulid beetles (Carpophilus hemipterus L.) per flower. These beetles are capable of transferring pollen from the stamens to the stigmas in the same flower or to other flowers at the time of anther dehiscence. Compared with insect pollination, wind and self pollination were low (< 2.0%).

The natural occurrence of nitidulid beetles in Annona flowers increased with increasing soil temperatures (range: 20-30°C) but were adversely affected by rainfall greater than 5 mm day^-1. The movement of beetles into the flowers may be low if more attractive food sources such as rotting fruit are continually available. Fruit set was also shown to be adversely affected by strong vegetative flushing.