Helophorus are mostly species of wetland habitats but there are a few exceptions. Our three species of the subgenus Empleurus, usually known as mud beetles, have in the past been pests of various crops although damage is rare nowadays. These are yellow or brown species identified by the presence of a short 'intercallary' stria between the base of the first and second complete striae, a lack of elytral tubercles (see tuberculatus below) and the presence of short stiff hairs on the tarsal segments rather than the usual fine hairs seen in all other British subgenera.
Helophorus nubilus Fab., the Wheat Shoot beetle, is active from May to September. Eggs are laid in the autumn and larvae are active from November, often feeding on winter wheat during bitterly cold weather when most other pests are inactive. They bite small holes or slits below the first leaf node or sometimes a little higher up so causing the central shoot to yellow while lateral shoots remain green, somtimes whole plants turn yellow and die. Damage is usually patchy but whole fields have been known to fail (Jones and Jones). The species is most common on light soils overlying chalk in the eastern counties. Larvae also occur on old established grassland.
Helophorus porculus Bedel and H.rufipes (Bosc d'Antic) are commonly known as Turnip Mud beetles. Adults and larvae cause damage to white turnip (Brassica rapa), often destroying the growing point; they tunnel into roots and stems and both stages feed on leaf edges. Swedes, beans, Kale, cabbage and lettuce are also attacked. Damaged swedes and turnips often rot in the ground. Eggs are laid in July and August, the resulting larvae feed through the winter to March when they pupate within earthen cells some 5cm below the ground. Attacks are sporadic and have been reported throughout the country (Jones and Jones ibid) although H.porculus is thought to have a more northerly distribution (Angus, 1978). Both species are occasionally found on sand dunes. Our three Empleurus species are keyed by Angus (1978), Friday and Hansen
Helophorus tuberculatus Gyllengal, our only member of the subgenus Cyphelophonus Kuwert, is a very distinctive species; about 3mm long, entirely black and with three rows of shiny elongate tubercles on each elytron. Although widespread it is of rare and erratic occurence, it generaly occurs on peat moss after this has been burnt, and in the field closely resembles a small piece of charcoal. While the species has fine hairs to the meso and meta tarsi, it does not live in water. Adults occur in wet moss (mostly Sphagnum) from March to August. During the spring they may be netted in flight, often far from their natural habitat. It is thought that winter is passed in the adult stage (Hansen).
Three more British species are characterised by the presence of an abbreviated stria between the base of the first and second complete striae.
Our only member of the subgenus Trichohelophorus Kuwert, H.alternans Gene (4-5mm), is distinctive in that the terminal segment of the maxillary palp is longitudinally symmetrical when viewed from any angle and the last (visible) abdominal segment is smoothly rounded. A very widespread and mostly coastal species although it also occurs in the New Forest, it is more frequent in the southeast. Keyed by Friday and Angus (1978) but not by Hansen.
The subgenus Megalohelophorus Kuwert includes two species, H.aequalis Thomson C.G (4.5-6.5mm) and H.grandis Illiger (5.5-7mm), both of which have the terminal segment of the maxillary palps asymetrical (may need to be viewed from several angles) and the last (visible) abdominal segment denticulate. Both are widespread and common and they often occur together. Keyed by Angus (1978), Friday (1987) and Hansen (1987).
Our remaining species lack the abbreviated stria between the base of the first and second complete striae.
Species of the subgenus Atracthelophorus Kuwert are distinctive in having the terminal segment of the maxillary palpi symetrical; viewed from above the inner and outer edges are of equal curvature. in Helophorus s.str. the outer edge of this segment is much more strongly curved. Breifly, our two species of Atracthelophorus may be separated by the form of the side margin of the pronotum; in H.avernicus Mulsant (2.7-3.5mm) it is sinuate in the posterior half while in H.brevipalpis Bedel(1.9-3.5mm) it is more or less straight. They also differ in the form of the palps and the genitalia. H.brevipalpis is common throughout Britain while H.avernicus is a mostly northern and western species occuring along the margins of clean and fairly rapidly flowing streams.
Our eleven remaining species are included in the subgenus Helophorus Fabricius and , for those without extensive experience, often present fomidable difficulties with identification and in most cases dissection is absolutely essential. It is pointless and, in any case, inappropriate to try to outline the identification of the individual species in this brief overview but the group does present the opportunity to discuss some aspects of Helophorus determination.
In each species there is a Y shaped groove on the vertex of the head, the stem begins by the front margin of the pronotum and the apices lie in front of the eyes. In most cases the stem widens considerably from its base to its anterior limit and, at least in all the cases we have seen, this widening is very obvious, often to the extent that the entire stem appears triangular. In three of our species, however the stem is narrow and parallel-sided, in some cases may be very slightly broader anteriorly but to nothing like the extent of those just described. H.laticollis Thomson C.G. , H.nanus Sturm and H.strigifrons Thomson C.G. have this narrow and parallel sided stem, our remaing members of the subgenus have the dilated form. H.nanus is distinct in possessing small longitudinal impressions on the vertex either side of the stem. H.laticollis and H.strigifrons are easiest separated by reference to another useful aspect of Helophorus identification; the elytral flanks. A very fine longitudinal line lying next to the outside margins of the tenth row of punctures forms the inner margin of the elytral 'flank' (referred to in Hansen (1987) as the pseudepipleura), external to this another fine line forms the outer margin of the flank and the inner edge of the true, reflexed elytral epipleur. Depending on the width and the orientation of the flank it may be visible when viewing the beetle from below, when this is the case the width of the flank relative to the width of the epipleur at, for reference, the level of the metacoxae provides an important diagnostic feature. Obviously the beetle needs to be viewed directly from above as any lateral tilt will exaggerate the view of one elytal flank compared with the other. Thus our remaining two species with narrow Y stems can be identified; in H.strigifrons the flanks appear as wide as the epipleurs while in H.laticollis they are not visible. There are confirming characters in the male genitalia. H.strigifrons is widely distributed and occasionally abundant in grassy pools while H.laticollis has a very restricted distribution; formerly from the Surrey heaths but now may only occur in the New Forest.
Our remaining eight species of Helophorus s.str. need to be dissected and the male genitalia compared with a set of figures for a certain identification, and even with good figures some experience may be necessary. Some of our species are common or even abundant; H.obscurus Mulsant and H.minutus Fab. are widespread pond species, H.griseus Herbst is a mostly eastern species occuring in fens and ponds. H.flavipes Fab. is a mostly southern species of acid water and sphagnum pools and H.fulgidicollis Motschulsky is a widespread saltmarsh species most frequent in the south.
All our species of Helophorus s.str are keyed by Angus (1978), Friday (187) and Hansen (1987), and all feature figures of the male genitalia, in this respect the work of Hansen is particularly recommended. For those interested in Helophorus identification and systematics three papers by Angus (1984, 1985 and 1986) should be consulted, these are often technical and become very involved, they also cover many non-British species but make fascinating reading and give an excellent insight to the family.
The above discussion is aimed at giving a brief overview of our species and it is hoped that interested parties might feel some of the fascination for the group that we experience and then follow up some of the references. Some species are very common and so it should be easy enough for the beginner to become acquainted. Thanks to the meticulous work and efforts of Robert Angus (1973) we also have a fascinating insight into Helophorus life histories, this work contains a key to the larvae of all British species (3rd instar) with the exception of tuberculatus, photographs (37!) of egg cocoons, a good line drawing of a whole larva as well as many line drawings and photographs of larval details. There are also enough references to keep the beginner happy for a good while. At the moment we think it unlikely we shall be able to feature the terrestial species and so we have given some information on their life cycles above. Of the remaining (wetland) species we have a few to feature and we will include details of life histories where possible on individual pages.
References
Angus, R.B. 1973 The habitats, life histories and immature stages of Helophorus. Transactions of the Royal Entomolgical Society of London 125(1):1-26
Angus, R.B. 1978 Key etc to British Helophorus species. Balfour-Browne Club newsletter, 11
Angus, R.B. 1984 Towards a revision of the Palaearctic species of Helophorus 1 Entomological review 63:89-119
Angus, R.B. 1984 Towards a revision of the Palaearctic species of Helophorus 2 Entomological review 64:128-162
Angus, R.B. 1986 Revision of the Palaearctic species of the Helophorus minutus group, with chromosome analysis and hybridization experiments Systematic Entomology 11:133-163
Hansen, 1987 The Hydrophiloidea of Fennoscandia and Denmark E. J. Brill
Jones, F.G.W and Jones, M. 1964 Pests of field crops W. Clowes and sons London.
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Helophorus
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Helophorus
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