A new Uropodina mite was collected from cocoons and the body of the African palm weevil (Rhynchophorus phoenicis Fabricius, 1801) in Cameroon. The new species belongs to the Uroobovella minima species-group; it differs from the previously described species in the dorsal and ventral setation in both sexes, and in the shape and sculptural pattern of the genital shield of the female. Original drawings and a description are given, accompanied by notes on the presumed biology and possible role in the biological control of African palm weevils.
INTRODUCTION
Uropodina mites are well-known members of the soil fauna. They reach maximum diversity in the tropics (Lindquist et al. 2009), but currently only 10% of the species are known from these regions. Cameroon, with 39 listed species (Wiśniewski 1993), is one of the better studied countries in the West Afrotropical subregion, but this number is very low compared with the well studied European countries.
The association of mesostigmatid mites with other invertebrates is a well-known phenomenon in acarology (Lindquist et al. 2009). Several groups of mesostigmatid mites have been found on the body of insects, especially on beetles. These mites do not parasitise their beetle hosts but use them as a means of transport only, otherwise known as phoresy (Szymkowiak et al. 2007). A good number of Uropodina mites constitute a characteristic group of phoretic mites, with their second nymphs (deutonymphs) often attached to their host by the anal pedicel. Nymphs of other phoretic groups attach to the host with their chelicerae (Macrochelidae) or leg claws (Parasitidae) (Szymkowiak et al. 2007). During the past hundred years, several new Uropodina species have been described from deutonymphal instars found on the body of beetles (Wiśniewski & Hirschmann 1993). Unfortunately, the described immature stages have fewer characters than the adults; hence exact identification of species based only on nymphs is more difficult or sometimes impossible.
MATERIAL AND METHODS
Specimens were cleared in lactic acid and drawings were made with the aid of a drawing tube. All specimens are stored in alcohol and on slides. The material has been deposited in the Soil Zoology Collections of the Hungarian Natural History Museum, Budapest (HNHM) and in the Natural History Museum, Geneva (NHMG). Abbreviations: h — hypostomal setae, St — sternal setae, V — ventral setae. All measurements and scale bars are given in micrometres (µm).
TAXONOMY
Genus Uroobovella Berlese, 1903
Uroobovella phoenicicola sp. n.
Figs 1–17
Etymology: The name of the new species refers to the name of the host species on which the specimens were found.
Description:
Female.
Length of idiosoma 460–490 µm, width 370–400 µm (n=4). Body shape oval, colour reddish brown.
Dorsal idiosoma (Fig. 1): Dorsal and marginal shields fused anteriorly. All dorsal setae smooth and needle-like, but differ in size; most setae long (ca 30–40 µm), but several central setae short (ca 14–15 µm). Marginal shield smooth and bearing long (ca 30–35 µm) and needle-like setae (Fig. 2). Dorsal shield smooth, muscle scars present on caudal part of central area.
Ventral idiosoma (Fig. 3): Sternal shield smooth, all sternal setae needle-like, St1–St7 short (ca 11–12 µm), St8 long (ca 22 µm). St1–St3 situated near anterior margin of genital shield, St4 at level of posterior margin of coxae II, St5 at level of anterior margin of coxae III, St6 at level of central area of coxae III, St7 at level of anterior margin of coxae IV, St8 placed near basal edges of genital shield (Fig. 4). Ventral shield smooth, several oval pits situated at level of anal opening. Ventral setae smooth and needle-like, V1, V3 and setae around anal opening short (ca 13–17µm), other setae on ventral idiosoma long, postanal (ca 41 µm) and two posterior setae (ca 50–55 µm) longer than other ventral setae (ca 35–40 µm). Two pairs of lyriform fissures present near pedofossae of leg IV. Stigmata situated between coxae II and III. Peritremes hook-shaped, poststigmatid part short (Fig. 5). Genital shield of female scutiform, placed between coxae II and IV, without sculptural pattern and anterior process (Fig. 4). Pedofossae deep, their surface smooth, with separate furrows for tarsi IV, metapodal lines absent. Base of tritosternum narrow, its laciniae marginally serrate and apically divided into four branches (Fig. 6).
Gnathosoma (Fig. 7): Corniculi horn-like, internal malae smooth and as long as corniculi. Labrum marginally pilose. Hypostomal setae: h1 long (ca 61 µm), smooth and setiform; h2 short (ca 39 µm), robust and marginally serrate; h3 long (ca 57 µm) and basally serrate; h4 short (ca 20 µm), robust and marginally serrate. Epistome basally serrate and apically pilose (Fig. 8). Chelicerae with internal sclerotised nodes, fixed digit with apical sensory organ and longer than movable digit, both digits bearing a single tooth (Fig. 9).
Legs (Figs 10–13): All legs bear claws on tip of tarsi and have needle-like setae.
Male.
Length of idiosoma 460–470 µm, width 340–360 µm (n=4). Shape of idiosoma, ornamentation and chaetotaxy of dorsal parts as in female. Sternal setae short (ca 12–13 µm) and needle-like, St1–St4 situated around margins of genital opening, St5 at level of anterior margin of coxae III, St6 posteriorly to St4 and at level of central area of coxae III, St7 at level of central area of coxae III, St8 at level of anterior margin of coxae IV, St9 at level of central area of coxae IV Sternal shield smooth and bearing one pair of lyriform fissures near base of St1. Genital shield oval and located between coxae II (Fig. 14). Ventral setae and ornamentation similar to those of female.
Gnathosoma (Fig. 15): Corniculi horn-like, internal malae smooth and as long as corniculi. Hypostomal setae: h1 long (ca 74 µm), smooth and setiform; h2 (ca 50 µm) robust and marginally serrate; h3 (ca 46 µm) and h4 (ca 43 µm) marginally serrate. Other parts and processes similar to those of female.
Deutonymph.
Length of idiosoma 370–380 µm, width 270–280 µm (n=2). Dorsal idiosoma (Fig. 16): All dorsal setae smooth and needle-like, but differing in size: most setae long (ca 17– 20 µm), but several setae in central area short (ca 9–10 µm). Dorsal shield without sculptural pattern, several muscle scars present on caudal part of central area.
Ventral idiosoma (Fig. 17): Sternal setae short (ca 5–6 µm) and needle-like, St1 situated near anterior margin of sternal shield, St2 at level of anterior margin of coxae II, St3 at level of posterior margin of coxae II, St4 in central area of sternal shield, St5 at level of anterior margin of coxae III, St6 at level of posterior margin of coxae III, St7 at level of central area of coxae IV, St8 near posterior margin of sternal shield. Sternal shield smooth, without sculptural pattern. Ventrianal shield smooth, with two pairs of setae (ca 5–8 µm). Peritremes long and S-shaped.
Larva and protonymph. Unknown.
Holotype: ♀ REPUBLIC OF CAMEROON: South West Region, Manyu Division, Ashum Village, from cocoons formed by Rhynchophorus phoenicis weevils, 25.iv.2011, J. Tanyi Tambe (HNHM, in alcohol).
Paratypes: All with same data as holotype: 1♀ 1♂ 1 nymph (NHMG, in alcohol); 2♀ 3♂ 1 nymph (HNHM, in alcohol); 1♀ (HNHM, on slide).
Note: The adults are from one Rh. phoenicis cocoon, and nymphs are from the body of the weevil.
Remarks: The new species is placed in the Uroobovella minima-group (Hirschmann 1989) on the basis of the shape of the idiosoma and peritremes, number of sternal setae, and the presence of claws on the tip of leg I. Up until now, 23 species have been described in this group, one of which is known only from the deutonymph stage (U. inhaerens (Vitzthum, 1921)). The sternal shield of this species is ornamented by oval pits, but it is smooth in the new species. Only male specimens of U. vietnamvarians Hirschmann, 1981 are known. The genital shield of this species is situated between coxae III and IV, whereas that of the male of the new species is between coxae II. The characteristic differences between the new species and females of the Uroobovella minima-group are given in Table 1.
Biology: Adult mites were obtained from cocoons formed by Rhynchophorus phoe-nicis Fabricius, 1801 weevils, while deutonymphs were collected from the body of this weevil. The deutonymphs are either attached to the body of the weevils or move freely under their elytra. Not much is known about the biology of the mite, but since the adults were collected in cocoons, we assume that the species is a predator and feeds on the eggs and/or other life stages of the weevils. It is also possible that the mites prey on nematodes, maggots, juvenile slugs, fungi and/or organic matter that clusters on and around the cocoons, and use the weevils as a means of transportation only.
Figs 1–3.
Uroobovella phoenicicola sp. n. female, holotype (Cameroon): (1) body, dorsal view; (2) ventral view; (3) lateral view.
NOTES ON POSSIBLE ROLE IN BIOLOGICAL CONTROL
The African palm weevil is a large, reddish brown to black weevil that is distributed throughout tropical Africa and is a true pest of members of Arecaceae (= Palmae) (Gries et al. 1994) and Poaceae (= Gramineae). In Cameroon, where the study was carried out, the larvae are commonly known as ‘tumbu’ or ‘tumbu for palm tree’ in pidgin English, but have different appellations according to the 270 spoken dialects. These larvae are eaten as a delicacy when seasonally available. They have a high fatty acid content, and are a source of proteins and carbohydrates (Ekpo & Onigbinde 2005) as well as essential amino acids. Moreover, medicinal value has been ascribed to the larvae (Nzikou et al. 2010; Zaid 1999). The pest status of the African palm weevil has already been established (Bong et al. 2008). The weevils cause severe damage as a result of active feeding on the palms but also serve as a vector for plant parasitic nematodes (Kanzaki et al. 2009). They therefore play a major role in crop damage and yield loss. Several strategies have been tried and implemented for the control of these weevils, such as felling of diseased palms, and the use of pheromone baits and traps. However, the only natural method in trial so far is the use of entomopathogenic nematodes (Zaid et al. 2002). If the new mite species is indeed an obligate predator on the eggs and of developmental instars of this beetle, it will be interesting to determine if in the future the mite can be used as a biological control agent.
Figs 14–17.
Uroobovella phoenicicola sp. n. male and deutonymph, paratypes (Cameroon): (14) intercoxal area of male; (15) ventral view of gnathosoma in male; (16) dorsal idisoma of deutonymph; (17) ventral idiosoma of deutonymph.
TABLE 1
Characteristic differences between the new species and females of the Uroobovella minima-group.
ACKNOWLEDGEMENTS
We thank the two anonymous reviewers for their constructive suggestions towards the improvement of this manuscript.
