Larval morphology ofMetaphycus flavusand its role in host attachment and larval cannibalism

Abstract

Metaphycus flavus (Howard) (Hymenoptera: Encyrtidae) is a facultatively gregarious endoparasitoid of soft scales (Hemiptera: Coccidae). When it develops in superparasitised hosts, the larvae often attack and consume brood mates six or more days post oviposition. Under our laboratory conditions (25 ± 1°C and 14 hours of light followed by 18 ± 1°C and ten hours of darkness in 50-70% R.H.), M. flavus eggs hatched three days after oviposition. Measurements of the mandibles and tentorium indicate there are four larval instars, and M. flavus reaches the fourth instar by day six post oviposition, and pupates on day eight. Thus, cannibalism among M. flavus larvae occurs during the fourth instar. During this instar, M. flavus larvae separate from their attachment to the scale cuticle, to which they were tethered by a respiratory structure during the previous three larval instars. Once detached, they are free to move within the scale, which increases the probability of larval encounters and aggressive behaviours. Moreover, the mandibles of the fourth instar are better adapted for fighting than are those of the first three larval instars, since they are larger and more sclerotized. The cranium and mouthparts of M. flavus have four different types of sensory organs, some of which are almost certainly olfactory, an unexpected function for a larva that presumably is surrounded by an aqueous medium where gustatory sensilla would seem to be more appropriate. The cranium also bears two pairs of what appear to be secretory pores.

Reproductive strategy as a major factor determining female body size and fertility of a gregarious parasitoid

“…The females of "gregarious" parasitoids determine how many eggs they will lay in a single host (Godfray et al, ). Although some of gregarious parasitoids are known to have sclerotized mandibles and can occasionally kill their intraspecific competitors (Tena, Kapranas, Walker, Garcia‐Marí, & Luck, ), one or more parasitoid larvae may complete development in one host (Boivin & Baaren, ). The quantity of food sources may even be excessive for one larva; however, there might be a lack of food sources for several larvae (Carbone‐Santolamazza, Nieto, & Rivera, ; Klomp & Teerink, ) Adult size of gregarious parasitoids decrease as the number of developing offspring increases in similar‐sized hosts (Kazmer & Luck, ).…”

Description and Biological Studies of a New Species ofMetaphycusMercet, 1917 (Hymenoptera: Encyrtidae), A Parasitoid ofCapulinia linarosaeKondo & Gullan

“…28,29 Among the factors that affect female: male ratios are the population density of the host and the parasitoid, mortality of immature parasitoid stages, and quality, age and size of the host, among others. 18,27,29,30…”