Metoecus paradoxus in The Netherlands (Coleoptera: Rhipiphoridae) Wijn and R.B. Heitmans & Theo M.J. Peeters HEITMANS, W.R.B. & T.MJ. PEETERS, 1996. METOECUS PARADOXUS IN THE NETHERLANDS (COLEO¬ PTERA: RHIPIPHORIDAE). - ENT. BER., AMST. 56 (7): 109-117. Abstract: Metoecus paradoxus is predominantly a parasitoid of Vespula vulgaris, but has a wide range of host species. Before 1966 there were only three records of this northern Palaearctic species from The Netherlands, but during the last three decades the beetle was present in ten of the twelve Dutch provinces. The beetle occurs in various rural and urban environments. In this paper we summarize the beetle’s complex life history and discuss the recent increase of records. Possible mechanisms for differential parasitism and coexistence of different Metoecus species are also discussed. W.R.B. Heitmans, Institute of Evolutionary and Ecological Sciences, University of Leiden, P.O. Box 9516, 2300 RA Leiden, The Netherlands. T.MJ. Peeters, Bachlaan 752, 5011 BR Tilburg, The Netherlands. Introduction Ramdohr (1813) first found the species emer¬ ging from a Vespula nest in Germany, but the Metoecus paradoxus (Linnaeus) belongs to biology and much of the beetle’s complex life- the subfamily Rhipiphorinae of which all spe¬ history was unravelled by Chapman (1870, cies are solitary, idiobiont parasitoids of the 1891, 1897). The more recent studies by fullgrown larvae of various taxa of solitary Spradbery (1973), Carl & Wagner (1982) and and social aculeate Hymenoptera. Species of Svâcha (1994) greatly contribute to the under¬ the genus Metoecus are exclusively found on standing of the general ecology and the host the eusocial Vespidae. relationships of M. paradoxus. These studies The Rhipiphorinae are widely distributed in may have stimulated entomologists to pay mo¬ tropical and subtropical areas. Only a few spe¬ re attention to the presence and habits of the cies occur in regions with temperate climates. species. In this paper we shall give a brief de¬ Metoecus paradoxus is found throughout the scription of the adult beetle and summarize its Palaearctic region, including almost all nor¬ life-history. The new localities and the former thern European countries, the northern parts of and present distribution are given for The the Mediterranean area and northern Asia as Netherlands. We also discuss the beetle’s far as Hokkaido, northern Japan (Csiki, 1913; abundance in wasp colonies, the possible me¬ Hattori & Yamane, 1975; Yablokhov-Khnzo- chanisms of host selection and the occurrence ryan, 1976; Lucht, 1987; Heitmans et al., of differential parasitism in different Metoe¬ 1994). The species was possibly introduced in cus species. the USA (Missouri) and in Brazil (Schilder, 1924), but recent records could not be found. Description and life-history In the most recent overviews only a few re¬ cords of the beetle are given from The The adult Metoecus paradoxus beetle can Netherlands (Everts, 1922; Brakman, 1966), easily be recognized by its relatively small but in the last decades the species is increa¬ head (fig. 1) with the eyes moderate in size, singly observed (Peeters, 1990; Langeveld, antennae pectinate with the third to tenth joint 1992; Knotters, 1994). The scarce findings of subequal in length bearing very long and slen¬ M. paradoxus may be closely connected with der thread-like prolongations in the male, an¬ its parasitic and largely cryptic way of life. tennae subpectinate in the female, prothorax 110 Ent. Ber., Amst. 56 (1996) \ Fig. 1. Metoecus paradoxus, male, head. Fig. 2. Metoecus paradoxus, female, dorsal side. as wide as long with a median furrow, elytra October. The adult insects do probably not 2.5-3.0 times as long as the prothorax, gradu¬ feed and are short-lived. Rouget (1873) repor¬ ally tapered and acuminate posteriorly, sur¬ ted 12 days for an extremely large female. Carl face closely and finely punctured (fig. 2). The & Wagner (1982) noted an average longevity colour patterns are remarkably variable: Rou¬ of seven days for females and eight days for get (1873) and Schilder (1924) distinguish 21 males. H. Vogel (personal communication) different colour varieties of which many com¬ kept five adult beetles (four non-reproducing binations are fairly well related to sex and the females, one male) alive for six days. The spe¬ host species. cies is univoltine. Metoecus paradoxus is often found in the Several authors observed that M. paradoxus nests of the common yellow jacket wasps of can lay hundreds of eggs in small (10-50) to lar¬ the genus Vespula (Hoffer, 1883; Newstead, ge clusters (500) (Rouget, 1873; Chapman, 1891; Tuck, 1897; Spradbery, 1973; Carl & 1897; Carl & Wagner, 1982). Usually the ova- Wagner, 1982). The beetle probably mates and rioles contain 600 to 700 mature eggs (Carl & always lays the eggs outside the nest. The fe¬ Wagner, 1982). The number of eggs may in¬ male deposits her small eggs (0.5 mm) in cre¬ crease with increasing body size, which is, in vices of decaying wood. The egg hibernates. turn, probably dependent on host size. Gradl The first larval instar is of the triungulinid (1879b) and Hattori & Yamane (1975) found form, which hatches the following spring or that beetles from host larvae in queen cells are summer. Vespula wasp workers that collect significantly larger than those from worker wood to build the nest may coincidently visit cells. In Dutch museums and private collec¬ natal sites of triungulinids. The phoretic first- tions the total body length of adult females va¬ larval instar clings to the body of the wasp and ries from 8.1 to 13.3 mm (n= 49). is carried to the wasp’s nest. After arriving in In contrast with the short life expectancy of the nest, the larva leaves the wasp and searches the adult beetles the triungulinids were obser¬ for a suitable host in the comb. The beetle lar¬ ved to survive at least two months without va uses one fullgrown wasp larva for its deve¬ food waiting for a carrier (Carl & Wagner, lopment and pupates in the cell that is closed 1982). Observations of emerging beetles du¬ by the wasp larva before it is almost complete¬ ring a period of about 12 weeks reflect the idea ly consumed by the parasitoid. Summaries of that triungulinids have gradually entered the the successive feeding processes of the larva nest during most of the summer period and its development to adult beetle are given in (Rouget, 1873; Hoffer, 1883; Tuck, 1897; Clausen (1940), Edwards (1980) and Svâcha Langeveld, 1992; Drees, 1994; Svâcha, per¬ (1994). The development from triungulinid to sonal communication). adult beetle is completed within 3.5 weeks. The beetles emerge from late July until early Ent. Ber., Amst. 56 (1996) 111 Localities and distribution patterns hern district of the province of Limburg. Records from the West Frisian Islands and The first beetle was recorded in The Nether¬ also from the provinces of Flevoland and lands in Soest in the province of Utrecht in Drenthe are still lacking. 1875 and several specimens were collected in Unlike former articles by Gradl (1879a, 1895 in Roermond (province of Limburg) 1879b) and Reineck (1909) and reference (Everts, 1876; van der Hoop, 1896). These re¬ books by Spradbery (1973) and Edwards cords from the nineteenth century are repre¬ (1980) that report Metoecus paradoxus espe¬ sented by specimens in the collections of the cially to occur in underground nests, we also National Natural History Museum (NNM, recorded specimens from nests in buildings. Leiden) and in the Zoological Museum of Many authors did not take into account that Amsterdam (ZMA). A third finding from subterranean nests were more frequently exa¬ Hulsberg (province of Limburg) was reported mined than ‘aerial’ nests (Hoffer, 1883; Tuck, by Schmitz (1936); this specimen is kept in 1897; Carl & Wagner, 1982). Ten of our 22 re¬ the Natural History Museum of Maastricht cent records came from pest control operators (NHMM). Riischkamp (1919) considered a (PCOs) who destroyed wasp colonies under previous record of one (male) beetle from roofs, in chimneys and in cavity walls. The Valkenburg (also from the southern part of beetle was also captured twice by light traps in Limburg) as erroneous and no such specimen Zuid-Limburg and also once in Rhoon and is present in the NHMM (F.N. Dingemans- The Staelduinse Bosch (province of Zuid- Bakels, personal communication). We do not Holland). Both male and female beetles are at¬ know why Everts (1922) still mentioned a new tracted to light. Single beetles were collected record from Valkenburg, but it is possible that in quite different localities: two specimens he pointed out another specimen that could not were found on a reed stem (.Phragmites aus¬ be traced by us. Brakman (1966) only refered tralis (Cav.) Steudel) in Zeist (province of to records of provinces and did not specify any localities. In this paper we therefore map the O before 1900 records over three periods starting with the ni¬ neteenth century, followed by the period from 1900 until the publication of Brakman’s list (1966) and the more recent period starting from 1966. Faunistic data were checked from the material deposited in different museum and private collections, from the records regis¬ tered by The Inspectorate of the Environment (= Afdeling Bestrijding van Dierplagen (ABD), Ministerie VROM) and from a num¬ ber of field observations. Fig. 3 gives the former and present distribu¬ tion of M. paradoxus in The Netherlands in 10 X 10 km UTM-squares. Before 1966 M. para¬ doxus was considered to be rare, as it was on¬ ly known from 3 UTM-squares. Since then the number of records has increased to the present 22 UTM-squares. M. paradoxus is present in many regions of The Netherlands, including Fig. 3. Records of Metoecus paradoxus in The Nether¬ the dunes and the Holocene coastal districts, lands.