(Coleoptera: Chrysomelidae) by Kd Elsey
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HOW ARDULA COLASPIDIS (ALLANTONEMATIDAE) N. SP., A NEW PARASITE OF THE GRAPE COLASPIS (COLEOPTERA: CHRYSOMELIDAE) BY K. D. ELSEY1) Tobacco Research Laboratory, Federal Research, Science and Education Administration, USDA, Oxford, NC 27565, U.S.A. Howardula colaspidis, a nematode parasite of the grape colaspis (Colaspis brunnea) is described. This species closelyresembles H. dominicki but can be distinguished from the latter by having fewer ovarian cells, a longer uterus, and a shorter vulva to tail tip distance in the infective female. Also, the parasitic female of H. colaspidis is longer and relatively narrower than that of H. dominicki. Juveniles exited from female beetles during oviposition and occasionally from beetle larvae, but not from parasitized male beetles. Parasitism did not appear to reduce the fecundity of the adult. Over a 2-year period, parasitism of the host insect declined from 24 to 3% in corn and soybean fields in northeastern North Carolina. Recently, Elsey (1976) reported a heretofore unknown species of Howardula parasitizing the grape colaspis, Cola.r pi.r brunnea (F. ) (Chrysomelidae). C. brun- nea can be a damaging pest to a number of crops, e.g., rice, corn, and soybeans. Economic damage occurs as larvae feed on roots of a susceptible crop that was planted in an infested field. Adult beetles are polyphagous. In North Carolina, C. brunnea has only one generation and its seasonal history is similar to that described by Lindsay (1943) in Iowa. The insect overwinters in the larval stage, adults are present from mid-June through August, and overwintering larvae are first found in July. Nematodes in the genus Ho2uardula are obligate parasites of members of three orders of insects (Coleoptera, Diptera, Thysanoptera) and of several species of gamasid mites. The life cycle of different species of Howardula nematodes is similar: adult parasitic females release eggs or juvenile nematodes into the hemo- coel of the host where the juveniles grow. Eventually they leave the host by either the digestive or reproductive tract. Once outside the host, the juveniles molt to adults and mate, and the infective females are then capable of penetrating a host larva. MATERIALSAND METHODS Adult parasitic female nematodes were dissected from adult or larval C. brunnea, heat killed, fixed in TAF, and mounted in glycerin by the "slow" method (Southey, 1970). Male and infective female adults were obtained by holding juveniles that 1) Present Address: U. S. Vegetable Laboratory, USDA-FR/SEA-SouthernRegion 2875 Savannah Highway, Charleston, South Carolina 29407, U.S.A. 55 were dissected from the body of a beetle in 5 ml of water in a syracuse dish. After ca. 72 hr, many of the juveniles had molted to the adult stage. These were heat killed, fixed in TAF, stained with cotton blue, and mounted in glycerin by Baker's rapid method (Southey, 1970). These nematodes were compared with specimens of Howardula dominicki Elsey and H. ?b yllotretae Oldham that were in the author's collection. The seasonal incidence of parasitism in a population of C. brunnea was moni- tored in a contiguous group of large soybean and corn fields near Plymouth, North Carolina from summer 1975 to fall 1977. The parasitism of the adults in 1975 was reported by Elsey (1976) and monitoring parasitism in the succeeding gener- ation of larvae was begun in spring of 1976. From then on, samples of C. brun- nea larvae or adults were taken every 1-2 weeks, except for November 17 to March 1, when only four samples of larvae were taken. Samples of adults were only from soybeans. The succeeding generation of larvae were sampled from the same fields, which were planted to corn in the next spring. C. brunnea adults prefer soybean foliage to corn foliage so the emerging adults migrated to soybeans. After this migration, adult and subsequent larval sampling was switched to the nearest soybean field. Adult beetles were collected from soybean foliage either by hand or with an aspirator. Larvae and pupae were taken from soil samples ( 1 5 cm deep by 10 cm diam) which were obtained with a golf cup cutter. As larvae tended to migrate vertically in the soil, the fall and winter samples were taken from 15 to 30 cm below the soil surface, whereas the spring and summer samples were taken from 0-15 cm below the soil surface (the soil on the farm was in the Hyde series, thermic typic umbraquults.). Larvae and pupae were separated from the soil cores by sieving and flotation. A core was placed in a 4-liter plastic bucket and ca. 500 ml of water. Then the soil and water were mixed by hand and poured through a No. 6 (opening 3.36 mm) sieve into another bucket to remove large bits of trash and finally through a No. 18 (openings 1.00 mm) sieve. Larvae could be found either floating at the water surface in the buckets or in the material remaining in the second sieve. The collected C. bru?7nea adults and larvae were either dissected to determine the presence of nematodes or held individually for biological studies at 20-26° C on red clover sprouts germinated on water agar in small plastic petri dishes (60 x 15 mm). In addition, a total of 372 C. brunnea larvae were held on clover- agar plates, usually in batches of 20-40 larvae, to determine whether juveniles of Howardula could be disseminated by C. brunnea larvae. The agar surface was examined every other day for juvenile nematodes; dead larvae were dissected to determine whether they were parasitized; and all the surviving larvae were dissected after 2 weeks. Also in 1977, two batches of 51 and 56 adult beetles were held individually on clover in agar plates. These insects were treated in the same way as the larvae except that the number of eggs laid was counted. Samples of 24-179 adult beetles were taken from eight moderately to heavily .