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Introduction

This paper is the third in a series of biological and systematic investigations of developmental characteristics in the genus Aphytis Howard (Hymenoptera: Aphelinidae).

The systematics of Aphytis has been based almost entirely on imaginal morphology, which often does not show strong interspecific differences. Other than pupal pigmentation, which has proved useful in certain cases (DeBach, 1959), characteristics of developmental stages have not been utilized as systematic tools in this genus. The first paper in this series (Rosen and Eliraz, 1978) presented the developmental history of the generotype of Aphytis, A. chilensis Howard, as a basic background study, and included detailed descriptions of the various developmental stages. The second paper (Eliraz and Rosen, 1978) presented a comparative study of larval characteristics of several species in five species-groups, and the present paper reports the results of a comparative investigation of meconial pellets in several species of Aphytis.

In most parasitic Hymenoptera, fecal material accumulates in the midgut throughout the larval feeding period, and is expelled, in the form of a meconium or meconial pellets, only when the blind midgut becomes linked with the proctodaeum prior to pupation (Hagen, 1964). The meconia of numerous parasitic Hymenoptera have been occasionally described, but have not been used much as a diagnostic character for identification or classification. (Flanders (1942)) briefly discussed the meconia of several species, and concluded that “although larval meconium is of little, if any, value in identifying the species of a genus, it may be of value in the recognition of the species which compose the parasitic fauna of a host in the field.” More recently, Viggiani (1969) has shown that the shape of the meconia may be used to separate certain eulophid parasites of leaf-mining insects.

All the known species of Aphytis are ectoparasites of armored scale insects, developing externally on the bodies of their hosts beneath the covering scale (Rosen and DeBach, 1976). Their distinctive meconial pellets are very conspicuous under the scale, and have been noted by some of the early workers. (Quayle (1910)), for instance, described the meconia of A. chrysomphali (Mercet) [erroneously recorded by him as A. diaspidis (Howard)] as follows:

“Always accompanying the pupa are from six to ten black or dark brown torpedo like bodies .125 mm. long and .055 mm. broad, which are evacuations from the digestive tract and are expelled by the larva preliminary to pupation.”

Similarly, (Taylor (1935)), in his description of (presumably) the same species, wrote:

“No excretion occurs until the larva is ready to pupate. The excrement is in the form of small, shiny, black or brown bodies, bluntly pointed at each end—and usually 5 or 6 in number, and uniform in shape. They are deposited inside the scale, round the posterior end of the larva, and are so conspicuous in Aspidiotus destructor that they are very useful as a means of detecting the full-grown larvae or pupae in situ.”