APIONINAE Schönherr, 1823
A very diverse group with many abundant species, likely to occur wherever the host plants are found. Includes some of the most common British weevils.
Around the World
This large group of very distinctive weevils is now included as a subfamily of the Brentidae Billberg, 1820; the species are so broadly similar as to form a natural group that proves difficult not to recognize as a subfamily in its own right. The vast majority of the species were formerly included in the single genus Apion Herbst, 1797. The family is cosmopolitan and more than 2000 species have been described, more than 500 are Palaearctic and more than 300 occur in the Nearctic region but there are large numbers among other faunas that await description e.g. in Australia where exhaustive keys have not been written partly because of the large number of undescribed specimens. Various modern classifications have included the Nanophyinae Gistel, 1856 as a subfamily of the Apionidae but these are readily separated by the geniculate antennae; in Apioninae they are always orthocerous. Several other groups also lack a distinct antennal scape but are otherwise distinct; Anthribidae Billberg, 1820 lack the long rostrum and compact antennal club seen in Apioninae, Nemonychidae Bedel, 1882 are generally larger and posses a loose 3-segmented antennal club and are, in any case, sufficiently distinct for the purpose of identification, attelabids and rhynchitids are similarly distinct on overall morphology; posses a loose antennal club and have either connate claws (Apoderus and Attelabus) or have distinct teeth on the outside margin of the mandibles (Rhynchitids). In all cases the apions will become immediately recognizable by their overall appearance with a little experience. Classifications vary widely and it is likely to be some considerable time before a more complete knowledge, including descriptions of more regional faunas, is available. The modern system includes the single tribe Apionini Schoenherr, 1823 with most genera included within 15 subtribes. Members of the subfamily are distinguished in general by the form of the body and more especially of the appendages. Rostrum prostrate, eyes separated from the anterior pronotal margin by a distinct neck. The pronotum narrower than the elytra, quadrate or nearly so, slender and weakly rounded, parallel or subconical. Prosternum visible anterior to the procoxae. Pronotal and elytral bases smooth. Elytra generally widest at or behind the middle. Femora and coxae separated by elongate trocanters. Antennae not geniculate; funiculus 7-segmented, only rarely with 6 segments. Maxillary palpi 2-segmented, labial palpi single-segmented.
Perapion hydrolapathi larva
The Apioninae includes most of the European and North American species of the family. All are small weevils <5mm with an elongate and discontinuous outline; the elytral base is usually distinctly broader than the pronotal base and often abruptly and widely so, where the shoulders are broadly rounded and convex this often indicates a fully-winged condition. The name Apion means pear in Greek and obviously refers to the shape of the elytra which are typically pyriform but vary from elongate and rather parallel e.g. in Stenopterapion Bokor, 1923 or Squamapion Bokor, 1923, to broadly expanded as in Protopirapion Alonso-Zarazaga, 1990. Convexity varies; most species are moderately convex but some are flattened e.g. some Squamapion while species of Protapion Schilsky, 1908 and some Exapion Bedel, 1885 have highly arched elytra. The entire upper surface is usually pubescent, often only very finely so, but this may be dense and form distinct patterns e.g. in Ixapion Roudier & Tempére, 1973 or Taeniapion Schilsky, 1906. Colour varies but most species are dark, grey to black, and many have a distinct and often vivid metallic reflection, a few are pale and members of Apion Herbst, 1797 are completely bright red. The head is generally quadrate and variously punctured and microsculptured, sometimes glabrous and variously striate towards the base and behind eyes which are entire, round or elliptical and vary from almost flat to very convex and discontinuous with the outline. The vertex is sometimes impressed, sometimes strongly so e.g. in Aspidapion Schilsky, 1901 or Diplapion Reitter, 1916, or may have longitudinal keels. The ventral margin of the eyes is often clothed with a distinct margin of scale-like pubescence. The rostrum is usually long and downward curved, least so in some male Perapion Wagner, 1907 and most developed in female Rhopalapion Schilsky, 1906. It is often dilated near the antennal insertions and sometimes toothed or characteristically narrowed e.g. in species of Oxystoma Duméril, 1806. The scrobes are usually low down on the lateral surface, and in some genera e.g. Cynapion and Oxystoma they are enlarged. The antennae are 11-segmented and inserted laterally, only rarely appearing to be geniculate e.g. in some Protapion species, the second segment is usually larger and expanded apically, forming a scape, the funiculus is 7-segmented and the club 3-segmented and compact; it sometimes appears 4-segmented as the apical segment may be subapically constricted. The pronotum is generally quadrate or nearly so and always lacks lateral borders, it is often constricted before the anterior and posterior angles and the sides are generally straight or weakly curved, the dorsal surface is variously convex and usually has a median basal fovea which may extend to the middle or even the apex. The punctation varies from very faint, as in Acentrotypus Alonso-Zarazaga, 1990, to strong, dense and confluent. The scutellum is usually visible, an exception is Synapion Schilsky, 1902, and sometimes the surface is carinate or longitudinally grooved e.g. in Aspidapion. The abdomen has five visible sternites although the first two are fused and generally longer than the others combined. The procoxae are close together and closed behind, the prosternum being broadly visible anterior to these, the mesocoxae are close together but distinctly separate. The elytra are usually free and many species are fully winged; they completely cover the abdomen and are either continuously or separately rounded, elongate and usually broadest about or behind the middle. The striae are usually distinct and often strongly punctured, especially towards the base, the sutural striae usually does not reach the base, being abbreviated near the apex of the scutellum, and the outer striae, 6-8 are usually absent below the humerus, the ninth stria is always short; ending at the level of the metacoxae. Rarely they may be very fine or almost obsolete e.g. in Acentrotypus. The interstices vary in width and may almost equal the striae e.g. in Kalcapion Schilsky, 1906, although in general they are broad, well defined and lack large punctures, the surface varies from weakly concave to flat or convex and they are variously punctured and microsculptured. Legs usually long and slender with smooth femora . Tarsi 5-5-5 with the third segment strongly bilobed and the fourth tiny and likely to be overlooked. Claws equal in length and free, sometimes with a basal tooth. Males are generally narrower than females and in some species they are consistently smaller, sometimes there are colour differences between the sexes and in females the rostrum is usually longer.
Zetophloeus brevicornis (Brentidae)
APIONINAE is now included in the BRENTIDAE
All species within the subfamily are phytophagous both as adults and larvae, and most are oligophagous; in general the members of a genus feed upon members of a particular plant family. A species may be oligophagous over part of its range and monophagous over other parts, and very few species are truly monophagous. For the majority of temperate species the host associations are well documented and in most cases they are herbaceous dicotyledons, very few are monocotyledons. Most species overwinter as adults, generally in the soil near the host or remote from it; those overwintering near the host emerge from the soil in the spring and feed for a short while before mating although some specimens will mate in the autumn and then it is generally only the females that overwinter. Those overwintering remote from the host include species of Ceratapion, Apion, Catapion, Cynapion and Eutrichapion, and all species of Oxystoma are known to do so, these species disperse in the autumn to forest margins and hedgerows etc. and at this time may occur on the foliage of trees and shrubs in numbers before they enter the soil to overwinter; in the spring they emerge and fly in search of host material and are very adept at locating it. Often only a proportion of the population will disperse in the autumn while some remain near the host, those dispersing rarely become sexually mature until after the period of spring migration back to the host. Hence some species will be found for a short period in the spring and autumn on tree and shrub foliage away from the normal host. Some species may be very local, even to the extent of occurring over several years at a single location within an area where the host is common and widespread and so working a local area thoroughly may take many years; those that disperse may be expected to arrive at any time. Flight ability varies even within a genus and some species of Protapion are known to fly while others disperse by walking between plants. Some species have been recorded at light traps. In some species there is an autumn brood, some Exapion produce a partial autumn generation which will overwinter as eggs and larvae in the host seed pods, here the resulting adults do not become mature until the spring and will breed alongside those that have overwintered.
There is usually a single generation with adults living over two years, from autumn to spring, and it is likely that they die out before the late summer generation of adults emerge. The appearance of the adults depends on the season but in general they appear early, often coinciding with the emergence of the hosts, and after a period of maturation feeding they breed in late spring and early summer; oviposition begins in late spring and, unusually, continues through the summer into August. Females bore into host stems, leaves, roots and buds etc. and insert single eggs, or rarely more than one, and seal the site with an abdominal secretion to prevent them from drying out. The larvae emerge quickly and feed within the plant tissue, generally developing rapidly and becoming full-grown within six weeks under good conditions. Some species are more specialized feeders e.g. some Apion are leaf miners while some develop in rolled up leaves, Pirapion live within flowerheads which fall to the ground after they commence feeding, Melanapion minimum (Herbst, 1797) larvae develop inside abandoned Hymenoptera galls and the Nearctic Podapion gallicola Riley, 1883 develops in galls on young pine twigs. Ixapion variegatum (Wencker, 1864) is a specialist mistletoe feeder. Pupation generally occurs within the host tissue without the construction of a pupal cell; this stage is brief and typically lasts about a week. The duration from egg to adult is on average about six weeks across the subfamily and it is thought that in warmer climates there may be more than a single generation each year. More than half of all known species are associated with members of the Fabaceae, peas and beans etc. and many are associated with Asteraceae, Polygonaceae, Labiatae, Malvaceae and Lytraceae. Some species are pests of commercially grown legumes; members of Protapion develop within flowerheads and destroy seeds etc. Ischnopterapion virens (Herbst, 1797) larvae feed within the stems of Trifolium pratense, and those of Holotrichapion pisi (Fabricius, 1801) feed within the stems of Medicago lupulina L. A few species have been tried as biocontrol agents for invasive weeds introduced from Europe into several areas; Stenopterapion scutellare (Kirby, 1811) and Exapion ulicis (Forster, 1771) on Ulex europeus and Taeniapion urticarium (Herbst, 1784) on nettles.
The U.K. fauna is fairly representative of the subfamily as a whole, if not in terms of species then certainly in terms of diversity; about 90 species included in 34 genera and 10 tribes are listed and new species are added at regular intervals. All but two of our species occur on herbaceous plants; Betulapion simile (Kirby, 1811) is widespread and locally common on birch while Melanapion minimum (Herbst, 1797) is a local southern species occurring on willows. Several very common plants host a range of species and, when the host is properly identified, some of these will be easy to identify, more especially species of Apion s.str. from various Rumex, several genera from mallow, gorse and broom, and Taeniapion from nettles. Lists of host plants can be found on line and there are several very good published keys that cover our list. Mercifully some of our more common species are easy to identify and so will serve to introduce the group but many are difficult and reference material may be essential but over time the various species as well as the use of the keys becomes familiar, using several keys together along with on line sources of good photos will make the task much easier.