FNZ 13 - Encyrtidae (Insecta: Hymenoptera) - Biology and Life History
Noyes, JS 1988. Encyrtidae (Insecta: Hymenoptera). Fauna of New Zealand 13, 192 pages.
( ISSN 0111-5383 (print), ; no. 13. ISBN 0-477-02517-X (print), ). Published 09 May 1988
Biology and Life History
A review of encyrtid biology is given by Clausen (1940), and surveys of the hosts of encyrtids are presented by Trjapitzin (1972) and Tachikawa (1981). With but a few exceptions - Microterys species, predators of the eggs of Coccidae; see Silvestri (1919b), DeBach (1939), and Sugonjaev (1934) - all species of Encyrtidae for which the biology is known are internal parasites or hyperparasites of holometabolous insects, spiders, ticks, and mites. They are most commonly associated with species of the superfamily Coccoidea (Homoptera). Encyrtids may be solitary, or gregarious (several parasites living within a single host, e.g., some Metaphycus species), or polyembryonic (more than one individual developing from a single egg, e.g., Copidosoma species).
Species of encyrtid may be either arrhenotokous (biparental reproduction) or thelytokous (males not known, or rare). Sometimes a single species can exhibit both types of reproduction depending on the location of the population. A species that is normally arrhenotokous may become thelytokous at the natural limits of its range or if its range becomes accidentally extended, e.g., Protyndarichoides cinctiventris, which is biparental in Australia but apparently uniparental in New Zealand. Conversely, species which are normally thelytokous may produce males if the ovipositing female is exposed to high temperatures during its development (Wilson & Woolcock 1960a, b; Gordh & Lacey 1976; Laraichi 1978) or a combination of high temperature and unfavourable host (Flanders 1942a). Biparental species may produce an abnormally high proportion of males if reared on an unusual host (Teran & DeBach 1963). The food plant, or the condition of the food plant fed upon by the host, may also affect the sex ratio of the parasite (Flanders 1942b).
The encyrtid egg is dumbell-shaped. The swollen part of the egg which contains the embryo is connected to a second swollen part (the bulb) via a narrow tube (the neck). The bulb may be larger or smaller than the part containing the embryo. Parts of the connecting tube and the egg proper may have a conspicuously sculptured appearance, this area most commonly being called the aeroscopic plate. Eggs without an aeroscopic plate are generally deposited free within the host, but those with an aeroscopic plate are deposited so that the neck of the egg passes through the host's body wall and the bulb is external. The aeroscopic plate aids the respiration of early-instar larvae which possess an open (metapneustic) tracheal system by conveying atmospheric air to them. Such larvae stay attached to the remains of the egg after hatching, whereas early-instar larvae without open tracheal systems become detached from the egg after hatching. The different types of egg found in the Encyrtidae have been described by Silvestri (1919a, b), Parker (1924), and Maple (1947).
The larvae of encyrtids vary from almost spherical to oval or broad at the head end and tapering towards the tail, which may be bifurcate. The first-instar larva may be apneustic (without spiracles), obtaining oxygen by diffusion from the body fluids of the host, or it may be metapneustic (possessing a pair of functioning terminal spiracles), having access to atmospheric oxygen by means of the aeroscopic plate of the egg. So far as is known there are either three or four larval instars, depending on the species. The final-instar larva has been reported as having between eleven and fourteen segments. Nine pairs of spiracles are present, on segments 3-11 or 4-12. The larvae of various encyrtid species have been described and figured by Silvestri (1919a, b), Parker (1924), Chumakova (1961), Kfir & Rosen (1980), and Rosen & Alon (1983).
The encyrtid pupa is formed within the integument of the host (except probably in Microterys sylvius (Dalman)), after the entire body contents have been consumed and waste materials (meconium) have been voided into the cavity thus formed. Some species even pupate within the living host, killing it only when the adult parasite emerges; e.g., Encyrtus infelix (Embleton) (Embleton 1904). The pupa is exarate, i.e., has the appendages free and visible externally. Pupae of various encyrtids have been figured by Taylor (1935), Kfir & Rosen (1980), and Rosen & Alon (1983).