FNZ 17 - Mymaridae (Insecta: Hymenoptera) - Biology and Life History
Noyes, JS; Valentine, EW 1989. Mymaridae (Insecta: Hymenoptera). Fauna of New Zealand 17, 100 pages.
(
ISSN 0111-5383 (print),
;
no.
17.
ISBN 0-477-02542-0 (print),
).
Published 28 Apr 1989
ZooBank: http://zoobank.org/References/1D0A405D-6643-42DB-B911-80664BC6F853
Biology and Life History
All Mymaridae are believed to be internal parasitoids of the eggs of other insects, and records of other hosts are almost certainly erroneous. For example, Lampel (1959) documented the supposed development of Polynema schmitzi Soyka in the nymphal and adult stages of the aphid Pemphigus populi-nigrae Schrank. However, his figures and description of the immature stages of the parasitoid are probably those of an aphidiine braconid. Most mymarids are solitary parasitoids, but gregarious parasitism does occur in some species, up to fifty individuals developing in a single host egg (Jackson 1956). Several species are known to be thelytokously parthenogenetic, that is females lay eggs that develop only into females, and males are unknown.
The majority of recorded hosts are the eggs of species of Sternorrhyncha (Hemiptera), but the eggs of other Hemiptera, Coleoptera, and Psocoptera are also commonly attacked (Huber 1986). Mymarids most commonly seem to parasitise eggs that are laid in concealed situations, such as those that are embedded in plant stems, placed under bracts, or hidden in the ground. Females seem to prefer eggs that have not undergone much development. After oviposition further development of the host egg normally ceases, but it is not known whether mymarids inject an arrestment venom during oviposition, as do many other egg parasitoids (Strand l986).
The mymarid egg is elongate-oval with a short pedicel at one end (Jackson 1961). The number of larval instars is difficult to ascertain, but from two to four have been recorded (Balduf 1928, Bakkendorf 1934, Sahad 1982).
The first-instar larva is generally either sacciform (a simple sac with few processes and no hairs) or mymariform (body curved, with a cephalic process, long caudal appendage, and long cuticular hairs).
The second larval instar of some species with a sacciform first-instar larva is very distinctive and is known as a histriobdellid larva. It is cylindrical and divided into 6 segments, the first and last segments largest, and often bearing paired fleshy processes (see Dumbleton 1934, Jackson 1961). The second-instar larva of other species is often without segmentation, spines, or setae. There appear to be no functional tracheae or spiracles in any larval instar.
Overwintering is normally as a mature larva in the host egg. Pupation normally takes place within the host eggshell.
Several extralimital species of mymarid are known to parasitise the submerged eggs of aquatic insects, e.g., Caraphractus cinctus Walker, a parasitoid of dytiscid (Coleoptera) eggs in Britain. To do this they are capable of swimming under water, using their wings as paddles (Jackson 1966; see also Matheson & Cosby 1912). Females need not leave the water immediately after emergence, and mating may also take place under water. Individuals are capable of remaining under water for 15 consecutive days (Rimsky-Korsakov 1933). The mymarid may leave the water by climbing the stem of a plant that breaks the surface.