Tachinids as parasites of injurious insects.
This a general review of the biology of the family Tachinidae, which includes about 5000 species and is distributed throughout the world. They are parasitic on insects and myriapods and among insects, their hosts belong to many orders and families. Some species are host specific, such as Cyzenis albicans (Fall.), which is restricted to Operophtera spp., while others are polyphagous, like Compsilura concinnata (Mg.) which is known to parasitise 98 species of Lepidoptera in 5 families and 5 sawflies in 3. Their importance can be great, as in Hyperecteina aldrichi Mesnil, which destroys some 90% of the adults of Popillia japonica Newm. in outbreak years in northern Japan and Urophyllina ussuriensis (Rod.), which infests an average of 20-25% of other cockchafer adults in the Maritime Province of the Soviet Union. The adults require supplementary feeding after emergence, pair usually in the morning, one male fertilising several females, and the females oviposit between 4 days and 2-4 weeks later. According to the mode of oviposition, tachinids fall into two groups. One lays eggs on or in the host insect, and such species usually lay only few eggs (100-200/female). Examples are given. The larvae usually hatch in 2-7 days and enter their hosts. The other group lays eggs containing larvae ready to hatch near prospective hosts or on their food-plants, and the newly hatched larvae seek hosts by active movements or the eggs are swallowed by them in feeding. The larvae are planidium-like in some species of this group that seek hosts, while the eggs of those that are swallowed are very small. Again, examples are cited. The larvae of tachinids develop internally in their hosts, with few exceptions. They feed only on the haemolymph or fat-body cells in their early stages but later attack the internal organs by means of digestive enzymes. However, Phasiines feed only on haemolymph or fat cells and their hosts therefore survive after the larvae have left them, though their ovaries become completely reduced and death follows through exhaustion and bacterial infection. Breathing is via the body surface or the tracheae of the host. Pupation is usually among host remains or in the cocoon of the host or in the soil. Various stages overwinter.