New Muscidae (Diptera) Hosts of Stylogaster Macquart (Diptera: Conopidae) from the Afrotropical Region

ABSTRACT An extensive collection of Muscidae, amassed through recent expeditions to Burundi, the Democratic Republic of the Congo, Kenya, Namibia and South Africa, is now deposited at the National Museum, Bloemfontein, South Africa. Twenty-five specimens of 14 species impaled with the eggs of Stylogaster Macquart (Diptera: Conopidae) were discovered among this material. New records of Stylogaster eggs are presented for four muscid genera: Afromydaea Malloch, 1930, Coenosia Meigen, 1826, Hebecnema Schnabl, 1889 and Pseudohelina Vockeroth, 1972, and for eight species: Afromydaea debilis (Stein, 1913), Coenosia ruwenzorica (Emden, 1940), Hebecnema semiflava Stein, 1913, Limnophora obsignata (Rondani, 1866), Pseudohelina nigritarsis (Jaennicke, 1867), Pseudohelina phaeoxantha (Emden, 1951), Pyrellina abdominalis Zielke, 1971 and Pyrellina versatilis (Villeneuve, 1916). A brief discussion of these associations is presented.


INTRODUCTION
Stylogaster Macquart, 1835 is a very peculiar genus of thick-headed flies, with an interesting and unique biology. The larvae are internal parasites and adult females have cha racteristic elongated ovipositors that are used to flick the eggs like darts into the host's cuticle. Hosts are predominantly cockroaches, crickets and calyptrate Diptera, and Stylogaster flies often target hosts attempting to escape columns of army ants (Hyme noptera: Dorylinae). Although commonly referred to as "hosts", it is believed that ca lyptrate flies are not the usual larval hosts, as larvae are infrequently found internally (Stuke 2012). Stuckenberg (1963) also questioned whether impaled flies are the final hosts or whether they transport eggs to their true hosts phoretically.
Stylogaster occurs in the New World, the Afrotropical Region (including Madagascar), parts of Asia, the Philippines, New Guinea, Eastern Australia, Tasmania and New Caledonia, but mainly in the Neotropical and Afrotropical regions (Smith 1967;Schneider 2010;Stuke 2012).
Afrotropical species were recently revised by Stuke (2012), who added 21 new spe cies, making a total of 34 valid species in the Afrotropical Region. Stuke also pre sented new faunistic records for nine previously described species, an identification key to Af rotropical species and a checklist with the revised and currently known dis tri bu tions.
Muscid flies (Diptera: Muscidae) have been recorded as frequent Stylogaster hosts and this association in the Afrotropical Region has been recently treated. Couri and Pont (2006) studied material from "An Arthropod Survey of Madagascar's Protected Areas (1998-2009" (housed in the California Academy of Sciences, San Francisco, USA) and recorded seven additional Madagascan muscid hosts, two for the first time. Couri and Barros (2010) recorded 15 specimens of Muscidae impaled with Stylogaster eggs, 14 from Madagascar and one from South Africa, belonging to 10 species, three of which were new records. These authors summarised records of Stylogaster Diptera hosts in Africa. The aim of the current paper is to record new African muscid hosts of Stylogaster with a brief discussion of this association.

MATERIAL AND METHODS
All material included in this study was sampled during recent expeditions to Burundi (2010), Kenya (2011) and three provinces of South Africa (2009)(2010)(2011)(2012) and is deposi ted at the National Museum (BMSA), Bloemfontein, South Africa.
Eggs were extracted from one specimen from Burundi (Pyrellina abdominalis), one from South Africa (Dimorphia tristis) and one from Kenya (Pseudohelina sp. 2). Infested flies were relaxed in a moist chamber for 24 hours, after which the egg was removed using entomological pins. It was macerated in 10 % potassium hydroxide for 24 hours, rinsed, dehydrated in alcohol and was stored in a microvial of glycerol pinned beneath the specimen.
Colour images were captured using Syncroscopy Auto-Montage with Leica MZ16 optical microscope.
New genus and species records are indicated with an asterisk (*), new species records alone with two asterisks (**).

RESULTS
Twenty-five specimens in 14 species impaled with Stylogaster eggs were discovered in the material (Table 1), from about 6,550 specimens examined in total. Four new generic records and eight new species records are noted.
Some eggs were situated in unusual body parts, difficult to access, such as the ventral part of the abdomen and between the two calypters (Figs 5-7).

Morphology of the eggs
Stylogaster eggs are yellow, elongate, with the anterior tip pointed, and possess one or two pairs of projecting barb-like spines. Some eggs have an eversible sac-like structure at the pointed apex, which is highly variable in shape and length among species (Stuckenberg 1963). All dissected eggs exhibited the same general morphology, with two pairs of short and closely-approximated lateral barbs (the dorsal a little shorter than the ventral), a short sculptured area behind the pointed apex and a short eversible sac (Figs 9-12). These are very similar to structures illustrated for an unidentified species of Stylogaster ex. Dichaetomyia sp. (Smith 1967 : fig. 17). Larvae may be observed in two of the dissected eggs.

DISCUSSION
Much remains to be discovered regarding the morphology of eggs and their associations with adult flies, a topic treated in a few papers, such as Stuckenberg (1963) and Smith (1967). Recently, the egg of S. hauseri Stuke, 2012, a Madagascan endemic, has been described (Stuke 2012). Couri and Barros (2010) attempted to identify eggs found in some muscid hosts by removing these from impaled pinned adults, but were unsuccessful, given that available information in the literature was insufficient and the key for identifying eggs (Smith 1967) only partial. Stuke (2012) noted that Afrotropical Stylogaster represent 30 % of the world fauna of this genus, with 68 % apparently restricted to Madagascar.
A brief discussion of the speculation on the association between muscid flies, Stylogaster and army ants was provided by Couri and Pont (2006). Since army ants are not found in some parts of Africa and Madagascar, it is clear that at least some species of Stylogaster are not associated with them (Stuckenberg 1963;Couri & Pont 2006).
As most of the muscid specimens attacked are females (72.6 %) (Couri and Barros 2010) and represent species attracted to faeces, it has been suggested that Stylogaster spp. may actively seek hosts in the vicinity of dung, where female flies are less active due to feeding or oviposition behaviour (Stuckenberg 1963;Smith 1969;Couri & Pont 2006). The current study confirms sex preference, with 88 % of attacked flies being female.
As regards the biology of the genera newly recorded here, Coenosia adults prey on other insects, both at the larval and adult stages; Pseudohelina lar vae occur in decaying vegetables and fruit, in which they are predaceous feeders; He becnema larvae are pre dators in ungulate dung (Skidmore 1985). Nothing is known about the biology of Af romydaea or Limnophora obsignata, although the larva of the latter probably occurs in dung.
It is intriguing to find eggs on the ventral parts of the host's body. It could be suggested that Stylogaster females hover below muscids while in flight and flick their eggs directly into the cuticle from beneath. This appears improbable, however, at least in the case of L. obsignata, which is a poor flier, occurring in the vicinity of streams and ge nerally flying from stone to stone.
Here, as recorded earlier by Couri and Pont (2006), the maximum number of eggs per specimen is three. Stuckenberg (1963) recorded a maximum of four and Smith (1967) five.