Placida

Abstract: Summary 1 Sacoglossan sea slugs (Gastropoda: Opisthobranchia) can change their highly specialized algal host associations in response to introduced hosts. 2 Adult sacoglossans (Placida dendritica) collected from the introduced green macroalga Codium fragile ssp. tomentosoides in west-coast Scottish sea lochs tended to associate with and consume introduced hosts over the native C. tomentosum in pairwise-choice feeding trials. 3 On west-coast Irish shores, where native congeneric hosts were more common, significantly more P. dendritica attacked C. tomentosum on the shore whereas Elysia viridis disproportionately attacked the exotics. In Lough Hyne, Co. Cork, Ireland, juvenile E. viridis attacked both C. fragile ssp. tomentosoides and the native, sympatric C. vermilara; in pairwise-choice feeding trials, sacoglossans preferred the host species from which they were collected. 4 In the Channel Islands, adult E. viridis were common on C. tomentosum on Guernsey shores. In pairwise-choice feeding trials adults exhibited no preference between native and introduced hosts, indicating that the stenophagous herbivores could change their associations. 5 On temperate Australian shores, the native sacoglossan Placida aoteana attacked the recently introduced C. fragile ssp. tomentosoides as well as native congeners and conspecifics. P. aoteana was common and its herbivory evident in Victoria and Tasmania. Slugs collected from native C. fragile exhibited no preference between algal subspecies in Victoria but a strong preference for the introduced subspecies in Tasmania. 6 Flexibility in host use enables stenophagous marine herbivores to respond within years to the presence of recently introduced hosts. The implicit peril of the host-specificity paradigm − that specialists could change their associations − does occur in stenophagous sacoglossans, and there is considerable intra- and interspecific variation in response. 7 Biological control of invasive green algae using sacoglossan herbivores is fraught with several risks, including taxonomic uncertainty of species’ boundaries, ecological flexibility of feeding, unexplored role of host susceptibility and insufficient evolutionary–developmental information to establish coevolutionary associations.

Abstract: The ultrastructure of the pathogen producing yellow-spot disease in the dendronotacean nudibranch Tritonia diomedea is described. A lamellar wall of thin scales, the morphology of the Golgi body, the presence of a putative bothrosome, and production of zoospores with mastigonemes indicate that the parasite is in the Thraustochytriaceae, a family of marine protists often included in the lower fungi. Host amoebocytes became greatly flattened and formed a lamellated wall around the parasitic cells, which finally were enclosed in a dense, thick-walled, acellular capsule where they were generally seen to be necrotic. The extensive encapsulation and necrosis suggested that the gastropod may be an unnatural host. The large dendronotacean nudibranch Tritonia diomedea is used extensively in neurophysiological studies. For a number of years, many specimens delivered to the Friday Harbor Laboratories on San Juan Island, Washington, have been afflicted with a parasitic infection known locally as the yellowspot disease or ringworm. The condition is characterized by the occurrence in the subepidermal tissues of yellow spots as large as 1.50 mm in diameter, and occasionally by erosion of surface layers. We describe here by electronmicroscopy the parasite and its encapsulation by amoebocytes of the host. Our primary purpose was to identify the pathogenic organism. Ultrastructural evidence indicates that the pathogen is a member of the Thraustochytriaceae, which are marine protists often included within the lower fungi. A secondary objective was to obtain information on the functioning of the encapsulating amoebocytes. Little is known about encapsulation of unicellular parasites in gastropods. Two relatively recent studies (Harris, 1976; Sullivan et al., 1978) show that metazoan parasites that remain viable when encapsulated in various snails are surrounded by amoebocytes that retain their cellular identity. In the present study, the amoebocytes surrounded the parasites as is expected in gasReceived 5 May 1981; revised 21 July 1981; accepted 19 October 1981. * Present address: Botany Department, The University of Georgia, Athens, Georgia 30602. tropods; but in older capsules they became dense and disappeared, and the parasites often were seen to be necrotic and encased by a thick, acellular wall. There are few reports on protistan or fungal endoparasites, or possible endoparasites, in the opisthobranchiate gastropods. The majority of these reports are notes within studies on other topics. Baba (1937) and Millott (1937) observed ciliates in the tissues of two nudibranchs. Eakin et al. (1967) reported small cells presumed to be symbionts in the eye of the nudibranch Hermissenda crassicornis. McLean (1978) described similar cells in many tissues of the sacoglossan Alderia modesta. Bruel (1940) detected an unidentified sporozoan infection in the sacoglossan Placida sp. A flagellate that parasitizes egg masses of doridacean nudibranchs was described by Zerling (1933), and Eliot (1910) briefly noted that "vegetable growths described as Phycomycetes" occasionally invade nudibranchs. The present study, therefore, is a contribution to a field in which little information is avail-

Abstract: Some sacoglossan molluscs, including several species of Elysiidae, are known to incorporate algal chloroplasts, and the incorporated chloroplasts are functional for days to months, depending on species. This incorporation and maintenance of foreign chloroplasts are known as kleptoplasty. In this article, we surveyed photosynthetic activity of several sacoglossans collected in Japan, by analysis of in vivo chlorophyll fluorescence. Our survey found 8 new species that have active chlorophylls, judged by the parameter Fv/Fm, an indicative of the functionality of photosystem II. Identified sacoglossans with active chlorophylls belong to the Bosella, Costasiella, Elysia, Julia, Placida, Stiliger, and Thuridilla genera. Our results strongly suggest that these species possess kleptoplasts. Possession of chloroplasts was confirmed for one of the identified sacoglossans, Elysia trisinuata, by transmission electron microscopy.

Abstract: Galerucella placida Baly (Coleoptera: Chrysomelidae) is a potential biocontrol agent of the rice-field weed Polygonum orientale L. (Polygonaceae). The volatile organic compound (VOC) profiles from undamaged and mechanically damaged plants, and from plants 12- and 36-h following continuous feeding of female G. placida adults and 2nd instar larvae were identified and quantified by GC–MS and GC-FID analyses. Twenty-four and 21 compounds were identified in volatiles of undamaged and insect feeding plants, respectively; whereas 22 compounds were detected in volatiles of mechanically damaged plants. Decanal and 1-dodecanol were unique to undamaged plants, and linalool was detected in volatiles of undamaged and mechanically damaged plants, but not in volatiles of insect damaged plants. However, the beetles are not attracted by none of these volatile components, when tested individually in Y-shaped glass tube olfactometer bioassays. In all plants, methyl jasmonate was predominant. 1-Undecanol was the least amount in undamaged plants, and plants 12-h after feeding by G. placida adults and larvae; whereas 1-tridecanol was the least abundant in plants 36-h after feeding by G. placida adults and larvae, and mechanically damaged plants. The beetles showed significant preference to the whole volatile blends from plants 12-h after feeding by larvae and plants 36-h after feeding by either larvae or adults compared to those of undamaged plants. Further, G. placida responded to individual synthetic compounds, 3-hexanol, 1-octen-3-ol, nonanal, and geraniol at 7, 1.38, 3.75 and 4.5 µg/25 µL CH2Cl2, respectively, and provide a basis for attraction of the potential biocontrol agent in the field.