Formicomus

Hemp, Claudia & Dettner, Konrad, 2003, Description of Larvae of the Genus Formicomus Laferté, and Data on the Life Cycles of Omonadus floralis (Linné) and Notoxus monoceros (Linné) (Coleoptera: Anthicidae), The Coleopterists Bulletin 57 (4), pp. 361-368 : 364-367

Based on the forementioned morphological data, Formicomus larvae may be integrated into the larval-key of the Anthicidae presented by Kitayama (1982):

8 Urogomphi with prominent chalazae on inner margin, one-third distance to apex - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 9

8 ' Urogomphi without chalazae on inner margin - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 10

9 Urogomphi with slight notch at base - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Sapintus vexator

9 ' Urogomphi with sulcus in base, no notch - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Vacusus

10 Urogomphi with large lateral chalazae - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Formicomus

10 ' Urogomphi without large lateral chalazae - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Notoxus

Rearing Larvae of Formicomus pedestris , F. gestroi , F. rubricollis , and Stricticomus amaniensis

Freshly hatched larvae were placed either on soil particles mixed with cow dung, vegetable detritus, or substrate to which fish food occasionally was added. Dark coloration of the gut indicated intake of material by the larvae. During the first 2–3 days the larvae grew from approximately 1.0 mm to 1.5 mm. Also, the faint cream colour changed to a light brown, and in particular the mandibles and urogomphi sclerotized, becoming darker brown.

None of the hatched larvae of F. pedestris lived longer than about 14 days, whereas all other species could be reared to adults.

Adults of F. pedestris were attracted from a wheat field which was fertilized with cow or pig dung. This is probably the basis for successful reproduction in this species. The adults seem to be polyphagous, and are not dependent on dung for nutrition. The larvae appear to require high humidity in loose soil enriched by organic materials of animal origin.

In rearing experiments with the species F. gestroi and F. rubricollis , which are widespread species in Africa south of the Sahara, larvae were kept in soil mixed with cow dung. In a period of about two months, larvae pupated in a pupae chamber made of soil, and 10 days later adults hatched. Larvae of both species were found in fertilized soil of cultivated areas ( Hemp et al. 1997).

Under similar conditions, the non-canthariphilous species S. amaniensis , which occurs with F. gestroi and F. rubricollis , was also reared. Females laid eggs into the upper surface of loose soil, that had been enriched with cow dung. A cycle from egg to adult was completed in a period of about 4 weeks.

Life Cycles of Omonadus floralis and Notoxus monoceros

Omonadus floralis . The European non-canthariphilous anthicid Omonadus floralis (Linne´) reproduces readily in boxes filled with sawdust to which fish food is added. Adults were collected from dung heaps at the end of April, and immediately started laying eggs and larvae soon appeared. When the first larvae were detected, the remaining adults were removed. About 6 weeks after the start of the culture, yellowish pupae were noted lying in the sawdust with or without a pupae chamber made of glued particles. Adults hatched from the pupae in an average of 6 days later. The 80 adults originally collected produced 200 beetles in the first generation in mid-June.

Populations of Omonadus floralis probably continuously build up several generations in the area surrounding Bayreuth/Northern Bavaria.

The larva of O. floralis was described by Rey (1887) and redescribed by Hinton (1945). Segment 3 of the antenna is long, while the sensory appendix is minute and cone-like, being half the length of segment three ( Figs. 16 and 19 ). The very small sensory appendix with a third antennal segment is present in Tanarthrus occidentalis Chandler and Sapintus vexator (Werner) ( Kitayama 1982) . Beside a small sensory appendix the genera Tanarthrus and Omonadus also share other morphological features, like small mesothoracic glands and similar shaped mesothoraces (Hemp unpubl. data). Urogomphal form and presence of chalazae ( Figs. 20, 22 ) are useful features in identification of anthicid larvae (see Kitayama 1982).

Notoxus monoceros . Notoxus monoceros is a frequently collected species in sandy habitats. In the area surrounding Bayreuth, specimens were attracted to cantharidin bait in a sandy wheat field. Females of mated Notoxus monoceros start laying eggs after 10 days. Adults were placed in 20 x 20 cm plastic boxes filled with about 3–4 cm of sandy soil from the wheat field. Females dug short tunnels to the bottom of the box for egg deposition, which were clustered in heaps of about 30. After 12 days larvae hatched and started feeding readily on fish food. After about 60 days the larvae became sluggish and started forming a pupal chamber of sand. Pupation lasts 12 days before the adults emerged. The sex ratio of hatched beetles was found to be 1:1. The life cycle of Notoxus monoceros thus is completed in about 3 months ( Fig. 23 ).

The first instar larva of Notoxus monoceros has well developed, rather slender antennae ( Figs. 17 and 18 ). The sensory appendix is as long as segment three, and is separated from segment three by a distinct gap ( Fig. 21 ). The urogomphi ( Fig. 22 ) do not show any projections or chalazae.

In the field adults were first attracted to cantharidin in April. Accumulation of cantharidin titres suggest (Schütz and Dettner 1992) that the first generation originates from larvae that have survived the winter, and have low cantharidin titres. The beetles continuously accumulate cantharidin, so that titres increase with the duration of life. The second generation in July is again marked by low cantharidin titres, which again increase with time till about October of the same year. The beetles of the second generation lay eggs that develop into larvae that overwinter, which was also proposed by Fey (1954). Görnitz (1937) reported that larvae close to pupation were found in a cultivated fields in early spring. N. monoceros apparently has two generations per year in Germany, which differs from the data of Fey (1954), who postulated only one generation per year for that species.

Single beetles were kept from the October generation in the laboratory at a temperature of 8 º C till spring of the following year. The longest life span of a female recorded was 194 days. Thus, it is possible that both larvae and adults of the autumn generation may survive the winter.

Figures

Figs. 9–22. Formicomus ssp., Omonadus floralis and Notoxus monoceros. Scanning electron micrographs of larvae. 9) Formicomus rubricollis, ventral view of the head (3433); 10) F. gestroi, ventral view of the head (3623); 11) F. pedestris, ventral view of the head (3963); 12) F. rubricollis, antenna, ventral view (1,5103); 13) F. gestroi, antenna, ventral view (9193); 14) F. gestroi, urogomphi, ventral view (4973); 15) F. pedestris, antenna, ventral view (1,4603); 16) Omonadus floralis, ventral view of the head (1103); 17) Notoxus monoceros, dorsal view of the head (1443); 18) N. monoceros, ventral view of the head (1583); 19) O. floralis, antenna, ventral view (6363); 20) O. floralis, urogomphi, dorsal view (1113); 21) N. monoceros, antenna, dorsal view (6003); 22) N. monoceros, urogomphi, lateral view (1263).

Fig. 23. Notoxus monoceros, life cycle.