Bulletin of Insectology 73 (2): 193-200, 2020 ISSN 1721-8861 eISSN 2283-0332 The ant host of Razorfemora zaragozae and some observations of their relationships under natural conditions Juan A. DELGADO1, R. Henry L. DISNEY2, Ricardo L. PALMA3 1Departamento de Zoología, Facultad de Biología, Universidad de Murcia, Spain 2Department of Zoology, University of Cambridge, United Kingdom 3Museum of New Zealand Te Papa Tongarewa, Wellington, New Zealand Abstract The biology of the scuttle fly Razorfemora zaragozae Disney (Diptera Phoridae) was previously unknown, but our observations in southern Spain indicate that this phorid fly is a parasitoid of the seed harvester ant Messor barbarus (L.) (Hymenoptera Formicidae). We report some aspects of the host location, host selection and oviposition behaviour of Razorfemora flies, as well as a potential defensive response of its host ant. Key words: Diptera, Phoridae, Razorfemora, scuttle flies, parasitoid, Hymenoptera, Formicidae, Messor, ants, behaviour, Spain. Introduction the species Razorfemora nussbaumi Disney from Israel, described from a single male (Disney, 1990). Disney Species of the dipteran family Phoridae are the most im- (1994) identified a female from Spain as R. nussbaumi portant parasitoids of members of the ant family Formi- but, when a large series of R. nussbaumi, including both cidae (Johnson, 2001). Since the review by Disney sexes, became available from Yemen, it was evident that (1994), many papers have focused on relationships be- the single female from Spain belonged to a second spe- tween parasitoid scuttle flies and ants (e.g. Hsieh and Per- cies (Disney, 2006). Since their description, nothing fecto, 2012; Mathis and Philpott, 2012; Elizalde et al., about the biology of the two species of Razorfemora has 2018). These publications contain descriptions of new been published. and interesting biological strategies and coevolutionary Because our initial observations during 2018 coincided relationships between both insect groups (Lachaud et al., with the beginning of the hottest season in southern 2012), including the role of phorid parasitoids in the bio- Spain, we obtained limited data. However, the discovery control of populations of ants of economic importance of what appeared to be a new host-parasitoid system be- (Bragança et al., 2017) and of invasive species (Chen and tween M. barbarus and R. zaragozae encouraged us to Fadamiro, 2018). continue our field observations during 2019. Therefore, Some ant communities, especially in the Neotropics, we decided to observe the temporal pattern of parasitoid appear to be heavily parasitised by phorids: army ants of activity of R. zaragozae towards M. barbarus during a the genus Eciton Latreille (Brown and Feener, 1998), complete annual cycle (figure 1). With some logistical leaf-cutting ants of the genera Atta F. and Acromyrmex constraints, we attempted (1) to gather data on the fly Mayr (Elizalde and Folgarait, 2012) and fire ants of the strategy to locate host colonies and select host individu- genus Solenopsis Westwood (Porter, 1998). However, als, (2) to describe the fly strategy to oviposit on a host, data from other type of ant communities or from other and (3) to analyse and interpret the putative correlation geographic regions are scarce (Disney, 1994). In the large between an observed posture taken by numerous ant arid and semiarid areas of the planet, harvester ants (seed workers of M. barbarus with a defensive mechanism. consumers) are of great ecological significance (Hölldobler and Wilson, 1990; Johnson, 2001). Regard- ing harvester ants, Disney (1994) cited some examples of Materials and methods the genus Pheidole Westwood, but Johnson (2001) stated that there were no records of phorid parasitoids associ- Material examined ated with species of the two most important genera in- Three specimens collected in 2018 were preserved in eth- habiting arid and semiarid areas: Messor Forel and Pogo- anol and sent to RHLD for their identification, who slide nomyrmex Mayr. Although Johnson (2001) referred to mounted them in Berlese Fluid (Disney, 2001). These the species of Messor from North America - now placed specimens are stored in the Department of Zoology at the in the genus Veromessor Forel - data are still lacking University of Cambridge, UK. Several additional females about species of Messor in the Palearctic Region. are stored in alcohol in the insect collections of the De- In a semiarid area of southeastern Spain, at the begin- partment of Zoology at the University of Murcia with the ning of the northern 2018 summer, we found a species of following data: 3 ♀ “SPAIN, Murcia, Near Molina de Se- phorid fly interacting with trunk trails of the harvester ant gura, 38.086650, -1.168354, 16/6/2018, J.A. Delgado Messor barbarus (L.), which appeared to be a host-para- leg.”, 2 ♀ same data except: 29/6/2018, 3 ♀ same data sitoid association. The phorid fly was identified by except 4/5/2019, 1 ♀ same data except 19/5/2019, 3 ♀ RHLD as Razorfemora zaragozae Disney (Disney, same data except 25/5/2019, 1 ♀ same data except 2006). The genus Razorfemora Disney was erected for 8/6/2019 and 2 ♀ same data except 29/6/2019. Figure 1. Annual cycle of five ant nests during 2019, summarizing the presence of (1) Razorfemora females, (2) ant workers in “c” posture and (3) ant colony activity in trunk trails (see text for further explanation of this figure). A total of 46 dead ants were collected from the studied colonies, and 60 individuals displaying “c” posture were also collected from trunk trails, to be examined under mi- croscope in an attempt to detect parasitoid eggs, larvae o pupae. Ants were cleared with potassium hydroxide and then stained with chlorazol black, to search for any evi- dence of parasitism. During May and June 2019, about 120 isolated head capsules of M. barbarus workers were collected and ex- amined in the laboratory. All were found to be com- pletely hollow and most without mouthparts. We also searched for fly pupae around the ant nest entrances, over an area of about one meter radius, concentrating our ef- fort on refuse piles (kitchen middens), which were col- lected and examined under a stereo microscope, but with- out finding any pupa. Methods It should be noted that this research was not initially designed, but it was developed from casual field obser- vations, which were later organised more systematically. Nevertheless, we feel that the data presented here, to- gether with our comments, even if some maybe specula- tive, still provide novel information about a parasitoid- host relationship. M. barbarus forms foraging groups to harvest seeds as its main food source, and is known to construct trunk trails (figure 2), which are cleared paths freed of Figure 2. Trunk trail of M. barbarus in the study area. 194 obstacles, debris and vegetation, radiating a few meters and Brown, 1997; Mathis and Philpott, 2012) have fol- from the nest entrance (Plowes et al., 2013). In order to lowed Vinson’s (1976) classification to arrange their ob- obtain a picture of the temporal variation of the ant col- servations and we also use this classification to organise ony and the fly attacking behaviour, we selected six dif- our field observations. ferent ant colonies and visited them weekly during the year 2019 (observations summarized in figure 1). De- pending on the climatic conditions of the day, visits to ant Results and discussion nests were made between 15.00 and 22.00 hours, lasting from one to one and a half hours for all nests. Preferably, Host habitat location we visited the colonies just before sunset avoiding the In the studied area, the activity of R. zaragozae females hottest hours of the day, especially in the summer period. appeared to be concentrated around the entrance of the We tried to spend at least ten minutes per ant nest. During ant colony as well as in the first meters of the trunk trails each visit we recorded the presence of R. zaragozae fe- made by the ants. A frequently observed strategy began males, taking notes on their behaviour, but we did not with female flies perching or resting in the vicinity of an collect them in every visit to reduce our impact on the ant nest entrance. After several minutes, they approached host-parasitoid relationship. When we collected flies, we the nest entrance and chose a victim leaving from or ar- made sure there was only one species of scuttle fly in the riving to the nest. A second strategy involved females pa- study area, although our previous experience showed that trolling up and down the main ant trunk trails along sev- Razorfemora was the only scuttle fly recorded here. eral meters (to a maximum of 7-8 meters from the ant When we found scuttle fly females attacking ants, we entrance) trying to parasitise one or several ant workers prolonged the observation of that ant nest from 10 to 30 (figure 3). minutes, thus reducing our observations of other nests M. barbarus uses trunk trails during a great part of its during that visit. seasonal activity. Working trails appeared in late Febru- Both, ant nest entrances and trunk trails were examined. ary or early March and, by early May, all colonies had As these trails experienced a seasonal variation in forag- them well established (figure 1). R. zaragozae adults ing activity over the course of the year (figure 1), we cat- seemed to coordinate their activity with the ants using the egorized the presence and approximate number of work- trunk trails. Probably, this is a strategy to find suitable ers in these trails, using a code number from 0 to 4, as hosts in high quantities. In addition, during this activity, follows: ants absent, generally due to overwintering or ants had their mandibles occupied with a seed, hence they aestivating nocturnal activity (0); dispersed worker ants were considerably less able to defend themselves.