Adosomus roridus

Trnka, Filip, Stejskal, Robert & Skuhrovec, Jiří, 2015, Biology and morphology of immature stages of Adosomus roridus (Coleoptera: Curculionidae: Lixinae), Zootaxa 4021 (3), pp. 433-446 : 441

Biology of Adosomus roridus

Habitat. Adults prefer dry, sunny places with host plants. In our study area, this species inhabited extensively used or fallow vineyards ( Figs. 5 D–E), ruderal vegetation and road edges in the vicinity ( Fig. 5 C). They inhabited both early and older succession stages of ruderal biotopes. Both adult individuals and immature stages were found in places with sparse vegetation, as well as in places with dense ruderal vegetation. Vineyard rows, where adults were often found, were manually or mechanically cultivated from time to time.

Adult behaviour. We usually observed adults under the host plant’s rosette ( Fig. 4 A) near the stem base. The adults are diurnal, and during sunny weather, they may climb up the host plant, even reaching the flowers. At night and in cold weather, these beetles are hidden under the rosettes of host plants. This species has very reduced wings (five specimens examined) and thus is most likely flightless. Adults can be observed from April to September. Published records of adults are available from the beginning of April to September ( Roubal 1937 –1941, Kofler 1962 –63). According to these findings, both larvae and some adults overwinter.

Host plants. Only adults of Adosomus roridus are known to feed on several Asteraceae : Artemisia absinthium L., A. vulgaris L. and Tanacetum vulgare L. ( Smreczyński 1968, Dieckmann 1983, Koch 1992). We observed that adults, especially at Tanacetum vulgare ( Fig. 5 A) and less at Artemisia vulgaris ( Fig. 5 B), preferred larger and older polycormons.

Life cycle. A female weevil bites the root neck/root of the host plant and lays an egg in the hole. The egg is 3 mm long and yellow ( Fig. 4 B). A mature larva lives endophagously in the root neck or root where it feeds on plant tissues ( Figs. 4 C–D). During its development, the larva causes a swelling of the root ( Fig. 4 E). Usually, only one larva occupies a plant, but rarely, there were 2– 3 larvae located on one plant; each larva created its own chamber. Mature larvae were found from the beginning of May to the second half of July. According to our observations, larvae of different instars overwinter and pupate the next year. Pupation occurs in the root neck/root. The new generation of adult beetles emerge from early summer to autumn. Some adults also overwinter, from early spring (beginning of April), which is supported by published data ( Roubal 1937 –1941, Kofler 1962 –63).

Rearing of the larvae. For laboratory breeding, 15 larvae were collected. Only older instars were able to be reared. Younger instars were hard to rear because the host plant root had a tendency to dry out and reduce its size, which led to destruction of the larva.

Figures

FIGURE 4. Adult and immature stages of Adosomus roridus (Pallas, 1781): A—adult, B—egg in roots of Tanacetum vulgare, C—mature larva in gall, D—mature larva (removed from gall), E—pupa in gall of Tanacetum vulgare, F—pupa (removed from gall).

FIGURE 5. Host plants and habitats of Adosomus roridus (Pallas, 1781): A—young host plant of Tanacetum vulgare, B—host plant Artemisia vulgaris, C – E: habitat in Slovakia (Pezinok-Grinava).