Oviposition of frit fly (Oscinella frit L.) on oat seedlings and subsequent larval development.
The following is virtually the author's summary of this account of observations in southern England. When undisturbed in a breeding chamber, females of Oscinella frit (L.) may lay many eggs behind a single coleoptile of the two- to four-leaf oat seedling. In the field, this happens only on plots free from predators or when fine weather at the end of May coincides with the two- to four-leaf stage. In other conditions, with predators active and other disturbing factors operating, 60% of all eggs are laid singly. When more than one larva penetrates the shoot, there is competition between them for food, and some fail to survive to pupation. Larvae can move between plants or tillers, but most that move in the field are probably killed by the predators Bembidian lampros (Hbst.), Agonum dorsale (Pontoppidan), Notiophilus biguttatus (F.) and Trechus quadristriatus (Schr.). These may also-prevent larvae that hatch from eggs laid on the soil from penetrating an oat seedling nearby. Dense stands of cereal are less favourable than sparse stands to the ovipositing female, probably because it is more difficult in the latter for the fly to position itself and there are fewer acceptable crevices. Counting eggs on plants in May is a better and simpler method of assessing populations than sampling by the small soil grab described by D. Webley (1957) or by assessing damaged shoots in June.