The Acroceridae (Diptera) of The Netherlands Herman de Jong, Aart P. Noordam & Theo Zeegers JONG. H. DE , A. P. NOORDAM & TH. ZEEGERS, 2000. THE ACROCERIDAE (DIPTERA) OF THE NETHER- LANDS. - ENT. BER., AMST. 60 (9): 171-179. , . j f thp Arrnreridae of The Netherlands. The current Dutch list contains 8 species of the swdv'of (he lectolype revealed that it is a female of P. orbiculus and the synonymy of P. boreal,s under P established Reticence considering the taxonomic status of other species names is expressed. A single ma e o . ƒ ttj^wafrearecHrornTsubadult female of Paräosa „Subns. which represents a new host record for this acroeend. H. de Jong. Afdeling Entomologie. Zoölogisch Museum. Plantage Middenlaan 64, 1018 DH Amsterdam, The A peNon„dlm. Afdeling Entomologie, Zoölogisch Museum, Plantage Middenlaan 64. 1018 DH Amsterdam, The Netherlands. Th. Zeegers, Weegschaalstraat 207, 7521 CH Enschede, The Netherlands. Acroceridae known from The Netherlands. Introduction The numbers of species of Acroceridae recorded from countries adjacent to The The recent rearing of a male of Ogeodes fuma- Netherlands are: Belgium: four (De Bruyn, tus (Erichson) by the second author and the 1991), Germany: 11 (Schumann, 1999; but see preparation of a new checklist of the Diptera the section on taxonomy), and Great Britain: occurring in The Netherlands induced this re¬ three (Chandler, 1998). The following collec¬ view of the Dutch records of Acroceridae. In tions with Dutch Acroceridae were studied in general, Acroceridae are seldom captured in the course of this project (abbreviations given the field and records are therefore scant. In his in parentheses): Nationaal Museum voor Na¬ checklist of Dutch Diptera, De Meijere (1939) tuurlijke Historie Naturalis, Leiden (NNM), recorded three species, viz. Oncodes gibbosus Wageningen Universiteit (WU), Zoölogisch (Linnaeus), O. zonatus Erichson, and Para- Museum, Amsterdam (ZMAN), and the pri¬ crocera orbiculus (Fabricius). Theowald vate collections of Bob van Aartsen, t Harde (1954) reported Oncodes varius Latreille as a (BvA), Laurens van der Leij, ’s-Hertogen- species new to the fauna. Van der Goot ( 1963) bosch (LvdL), Wouter van Steenis, Utrecht published a key to the then known four Dutch (WvS), Bastiaan Wakkie, Amsterdam (BW), species of Acroceridae, summarizing the lo¬ and Theo Zeegers, Enschede (ThZ). calities of capture from specimens studied and literature records. Van Aartsen (1997) added Acrocera trigramma Loew and Paracrocera Biology manevali Séguy to the Dutch list. In the pre¬ Although adult Acroceridae usually are sel¬ sent paper the published records are reviewed dom encountered in Northwest Europe, some and checked against material in Dutch collec¬ mass aggregations have been observed. In tions. As a result of this study we are able to England, Edwards (1983) recorded mating report the occurrence of Acrocera sanguinea clusters of Paracrocera orbiculus on the tips Meigen, Ogeodes fumatus, and O. reginae of dead elder twigs, a swarm of this species (Trojan) as new to the Dutch fauna. Paracro¬ flying about a group of elder leaves, and many cera manevali has to be deleted fiom the individuals of both sexes perched under termi- Dutch list, resulting in a total of 8 species of I 172 Ent. Ber., Amst. 60 (2000) Fig. 1. Eggs of Ogcodes gib- bosus (Linnaeus) on a stem of Equisetum fluviatile L. (photo A. P. Noordam). nal leaflets. Edwards (1984) observed several of true spiders (Araneae) and show hyperme¬ clusters of P. orbiculus, primarily consisting tamorphosis, i.e. the successive larval stages of males, on fence posts along a stretch of have a strikingly different morphology. about two hundred meters. A mass occurrence Usually a single parasitoid developes within a of Ogcodes reginae in a Molinia vegetation host specimen, but records are available of has been observed in the province of Noord two or more larvae reaching maturity in a sin¬ Brabant in The Netherlands (Van der Leij, gle spider. As the eggs are not deposited on 1999; as O. varius). According to the litera¬ the host, the first stage larvae must actively lo¬ ture, females of certain species tend to congre¬ cate their victim. The first instar larvae are of gate during oviposition, a phenomenon which the planidial type, i.e. they are flattened and is corroborated by some of the Dutch captures free-living. The first instar larvae move about of Ogcodes gibbosus (see under that species, by crawling, looping, or jumping. It is gener¬ below). Upon copulation, females deposit ally recorded that once a spider makes contact their eggs on dead twigs or branches (Ogco¬ with a planidial larva, the larva sticks to one of des) or on stems of grasses (Acrocera). A sin¬ its legs and climbs upward until it reaches the gle female may lay up to 5000 eggs. Figure 1 dorsal base of the spiders abdomen. This spot illustrates a stem of Equisetum fluviatile L. is unattainable for the spider’s preening legs. covered with eggs of O. gibbosus (material de¬ Here it cuts a hole and enters the abdomen posited in ZMAN). where it ends up in the booklung area. In a po¬ Primarily based on Schlinger (1987), the sition where it is able to breathe outside air, following information can be given on the bi¬ the larva goes into a phase of diapause which ology of immature Acroceridae. Larvae of lasts from five to nine months. The next two Acroceridae are obligatory internal parasitoids larval stages are rather little-known. A dif- 173 Ent. Ber., Amst. 60 (2000) ferent strategy was recently observed during consequence of the active search for a host by laboratory experiments by Overgaard Nielsen the first instar larva of the Acroceridae; active et al. (1999), who studied larvae of Paracro- search is hardly possible along sticky spider cera orbiculus invading Pardosa prativaga snares. The webbuilders on Schlinger s list (Koch). Here the planidial larvae attached frequently come into contact with the sub¬ themselves to the legs of the spiders, especial¬ strate (e.g. Zygiella in its retreat), or have the ly to the tibiae and femora, by cutting a small horizontal agelenoid web type. The last cate¬ hole through the integument. The spiders tried gory seems to be primarily parasitized by spe¬ to remove the ectoparasitic larvae, but often cialized New World acrocerids dropping their failed to kill them all. After about a week the eggs on these dense horizontal mats. Surpri¬ surviving larvae moulted and a small and flex¬ singly, there are no records of acrocerid para¬ ible second instar larva entered the host sitism in the Linyphiidae, which is by far the through the attachment hole made by the first most species-rich spider family in the temper¬ instar larva, leaving the entrance hole plugged ate regions. Linyphiidae are on average rather by the exuviae. The fourth and final larval small, but they make horizontal mats, while stage lasts only up to two days in the northern many linyphiids have frequent contact with European Acroceridae. During this stage the the substrate, and some have even evolved in¬ larva voraciously feeds on the internal tissues to hunting spiders and abandoned webbuild¬ of the spider and eventually emerges from the ing altogether. host. Ogcodes larvae emerge in the area of the epigastric furrow, Acrocera larvae leave the Hints for finding parasitized spiders host through the abdominal dorsum. About 24 hours before the acrocerid larva leaves its Several authors noticed the unchanged be¬ host, it apparently induces the spider to spin a haviour of the victim spider till the very end, small web reminiscent of a moulting web. The when it begins to build a web in which the spider will never use the web as it dies shortly acrocerid pupa will be suspended. Parasitism after completing it, but the parasitoid occupies in webbuilding spiders can perhaps be diag¬ the web in order to pupate in a protective en¬ nosed by disorders in the web many days be¬ veloppe. The adult fly emerges about two to fore the death of the spider. For Agelenidae, three weeks after pupation; adults live up to Cady et al. (1993) mentioned “poorly struc¬ six weeks. Rearing records indicate that spe¬ tured webs” which are not maintained. Holl et cific host-parasitoid relationships are rare. al. (1983) described one parasitized specimen of the orb web builder Zygiella x-notata (Clerck), of which the web consisted of only a Host spectrum few snares without an orb structure. However, Schlinger (1987) gave a world list of all this spider was detected only three hours be¬ known hosts of Acroceridae. On this list 22 of fore it started spinning the ultimate moulting a total of about 100 spider families are repre¬ web mentioned above. sented. Small spider species with an adult size In parasitized hunting spiders the retarded of less than 3 mm are lacking, apparently be¬ development can be a useful clue for detec¬ cause they do not offer enough nutriment for a tion. In the rearing of the Dutch specimen of parasitoid acrocerid to complete its develop¬ Ogcodes fumatus by the second author, the ment. Schlinger’s host list is dominated by parasitized spider was the most retarded of a hunting spiders, mostly Lycosidae and Sal- group of 25 specimens of Pardosa lugubris ticidae. The web building Agelenidae and (Walckenaer) collected simultaneously as Amaurobiidae are well represented, especially subadults and kept alive in order to record the in the New World, but other webbuilders are courtship. Dr D. Cordes (pers. comm.) had a nearly absent. The dominance of hunting spi¬ similar experience when rearing his only acro¬ ders and scarcity of webbuilders must be the cerid thus far. From a series of immature 174 Ent. Ber., Amst. 60 (2000) Alopecosa barbipes (Sundevall) all spiders tes for a possible synonymy are O.