Insect pests of fruit: fruit flies

The arrival of D. suzukii in Europe and America from Asia caused extensive damage to cherry and soft fruit strongly affecting their cultivation. Currently, to control the pest, there is an increase in the number of insecticide applications that are sprayed from fruit changing colour until the harvest period. This increase in use of chemicals has resulted in higher production costs, greater risk to consumers and the environment, compromise of current IPM strategies for other pests and may hasten the development of pesticide resistance. It is clear that an integrated approach to managing D. suzukii is required, as no one control option is sufficiently effective. Knowledge on the biology and ecology of any pest is a prerequisite to developing and/or improving an IPM strategy and consequently reducing the use of insecticides, and these have been extensively studied for D. suzukii since its invasion of North America and Europe. The numbers of D. suzukii trapped and the damage caused on different crops are highly variable between areas and location of orchards and the surrounding environment. Temperature, landscape composition and host plant abundance all play an important role on pest abundance and population dynamics. Studies show that catches and damage on fruit are higher at the margins of the orchards, close to hedges and forest, due to the presence of numerous host plants that provide food and refuge areas . Semi-natural areas have an important role providing alternative host resources, overwintering habitats, or refuge areas when crops are sprayed with insecticides, with implication on distribution and population dynamics inside the orchards. When the host plant was not suitable for reproduction, D. suzukii preferred to fly closer to the forest margin and near the grass. Differently, when the host plant was suitable, D. suzukii dispersed further into the orchards both horizontally and vertically. These gradients must be considered in the design of new orchards and in insecticide applications. In addition, catches and damage of D. suzukii are not uniform but vary widely depending between years. Years characterized by mild and humid winters, springs and summers are favourable for the development of pest, in contrast with cold, dry winters and hot summers. These considerations indicate the need for a management at agroecosystem level and not just limited to the orchard. All cultural and agronomical practices, in order to disadvantage the development of the pest, should be adopted in the orchard as pruning, mowing, borders management and ripe abandoned fruit destruction. Problems related with residues and side effects on the environment require careful management of chemical treatments, to be limited to the most sensitive fruit stages. It is of crucial importance that a rapid and timely harvesting of all fruits and proper management of discarded fruits . The wide-host range and natural habitats that harbour D. suzukii has led to the conclusion that an area-wide strategy is required to reduce populations of D. suzukii. Hence, biocontrol using natural enemies may play an important role in managing D. suzukii as part of an integrated pest management strategy. An area wide strategy which can suppress D. suzukii populations in the natural environment, where chemical pesticides cannot be applied, is required as part of an IPM programme. One such option would be biological control using natural enemies, and an Asian parasitoid (Ganapsis sp), which specifically attacks D. suzukii pupae, has the potential to fulfil this role. However, the release of non-native species in Europe is tightly regulated, and a risk assessment, including non-target impacts, must be undertaken as part of obtaining a licence for import and release of such parasitoids. Until such time, it may be worth pursuing the augmentative release of native natural enemies, and implementing attract and infect strategies using entomopathogenic fungi as tools in IPM strategies.