Ethiopian muscids (Diptera, Muscidae) egg-carriers of Stylogaster Macquart (Diptera, Conopidae)

Abstract

We here report for the first time on the presence of three species of the conopid genus Stylogaster Macquart (Diptera, Conopidae) in Ethiopia, viz. S. nitens Brunetti, S. westwoodi Smith and Stylogaster sp.. We further screened 908 muscid flies (Diptera, Muscidae) for the presence of impaled eggs of Stylogaster and recorded eggs on 89 individuals (9.8%). Eggs were impaled on eight species, viz. Limnophora translucida Stein, Musca lusoria Wiedemann, Musca splendens Pont, Neomyia chrysopyga (Emden), Pseudohelina nigritarsis (Jaennicke), Stomoxys omega Newstead, Stomoxys taeniatus Bigot and Stomoxys varipes (Bezzi). the maximum number of eggs found on a single muscid was six. We illustrated the dissected eggs. L. translucida, M. lusoria, M. splendens, N. chrysopyga and S. varipes are reported as new muscid hosts species for Stylogaster.

Oecanthus nigricornis(Orthoptera: Gryllidae) as the first known host ofStylogaster neglecta(Diptera: Conopidae)

“…Stylogaster species target nymphs and adult Gryllidae (Orthoptera) and Blattodea, whereas other conopid genera use adult aculeate Hymenoptera (Freeman 1966;Kotrba 1997;Woodley and Judd 1998;Schmid-Hempel 2001;Rasmussen and Cameron 2004;Marshall 2012;. Stylogaster eggs have been found on other species, such as other Diptera, but the lack of egg development indicates that these may be accidental ovipositions (Couri and Barros 2010;Stuke 2012;Couri et al 2019).…”

Stylogaster eggs on blow flies attracted to millipede defence secretions in Tanzania, with a stab at summarising their biology (Diptera: Conopidae & Calliphoridae)

“…This is further supported by records of larvae inside attached eggs, placed with their head towards the blunt micropylar end of the egg (Fig. 3D, Smith and Cunningham-Van Someren 1985, Couri et al 2013), and Stuckenberg (1963 found an empty egg attached to Dichaetomyia quadrata (Wiedemann) with the micropylar end "irregularly broken open" and interpreted this as a hatched egg. If the larva hatches from the egg through the end facing away from the host, especially for eggs that are attached to the ventral part of the host, it would appear that there is a high risk that the emerging larva would fall off the host.…”

“…Therefore, there is no firm evidence that these flies are regular or occasional hosts or even if they are hosts at all. It has been speculated that the calyptrate flies instead are used to transport the eggs to the final host or food source or that the flies just happen to share the same appearance or habitat as the host of Stylogaster and, therefore, accidentally become impaled with eggs (Smith 1967, Ferrar 1987, Couri and Pont 2006, Couri and Barros 2010, Stuke 2012, Couri et al 2013), but the evidence to support this remains circumstantial.…”

“…Many Stylogaster species are facultative army ant and driver ant followers (Carpenter 1914, Bequaert 1922, Bequaert 1930, Aldrich 1930, Lopes 1937, Cohic 1948, Rettenmeyer 1961a, Rettenmeyer 1961b. The females search for potential hosts in front of the leading edge of the advancing raids, looking for potential hosts fleeing from the ants (Stuckenberg 1963, Smith 1967, Smith 1969, Smith and Cunningham-Van Someren 1985, Kotrba 1997, Couri and Pont 2006, Couri and Barros 2010. When not following army ants, adults of Stylogaster can be found hovering over sunlit paths in the forest understorey or feeding off the nectar on small white or yellow flowers (Rettenmeyer 1961a, Burt et al 2014.…”

“…Firm evidence of actual parasitisation is still restricted to Smith and Cunningham-Van Someren (1985), who dissected larvae of Stylogaster from immature cockroaches, as well as from one cricket in Kenya; Woodley and Judd (1998), who reported Stylogaster biannulata (Say) as reared repeatedly from Gryllus rubens Scudder in USA, Florida;and Etzler et al (2020), who reared Stylogaster neglecta Williston from the cricket Oecanthus nigricornis (Walker) sampled from Canada (southern Ontario) and USA (New York State). The presence of Stylogaster eggs on various calyptrate flies has led to speculation about possible dipteran hosts, but as no larvae of Stylogaster have been found within any fly and no adults have been reared, this is still uncertain (Rettenmeyer 1961a, Rettenmeyer 1961b, Smith 1967, Smith 1969, Smith 1974, Smith and Cunningham-Van Someren 1985, Couri and Pont 2006, Couri and Barros 2010, Couri et al 2013, Couri et al 2019.…”