Molluscicidal activity of trifenmorph in field trials*

Bull. Org. mond. Sante 11973, 49, 377-379Bull. Wid Hlth Org. Molluscicidal activity of trifenmorph in field trials * B. GILBERT,1 C. CASTLETON,2 & M. S. BULHOES 1 Trifenmorph granules provided 100% control of Biomphalaria glabrata and B. tenago- phila when applied at 2 kg ofactive ingredient per hectare, except at one site with a pH of 5.6 where the snailpopulation was reduced by only 50%. Granulation wasfound to facilitate application by either hand or mistblower, and reduces the risk ofinfection to the spray team. Applied to canal margins the granules had a residual toxic effect. Trifenmorph has been shown by Boyce et al. (1) and Crossland (2) to be an effective molluscicide for controlling the intermediate snail hosts of the Schisto- somatidae. Paulini a reported that the application of wettable powders or emulsifiable concentrates requires the use of up to 10 1 of water for each 2-3 g of molluscicide and in highly endemic areas exposes spray teams to possible infection while fetching the large quantities of water necessary as a diluent or washing equipment after spray applications. Additionally, in irrigation or drainage canals with fluctuating water levels large numbers of snails re- main below the surface of the mud or aestivate along the edges, and are not reached by conventional molluscicides. The snails in aestivation may harbour immature stages of S. mansoni (4). An experimental granular formulation of trifen- morph containing 4% active ingredient was tested at 3 field sites in Brazil to verify its efficacy as a molluscicide and to establish the practicality of granules in terms of ease of application, reduction in hazard to spray teams, and residual action when applied to the margins of canals. MATERIALS AND METHODS Trifenmorph granules (4% active ingredient) b were tested against Biomphalaria glabrata or B. tena- gophila at the following sites. * From the Instituto de Pesquisas da Marinha and Centro de Pesquisas de Produtos Naturais, Rio de Janeiro, Brazil. 1 Research chemist (B.G.) and biologist (M.S.B.), Instituto de Pesquisas da Marinha, Rua Ipiru, Ilha do Governador, Rio de Janeiro, ZC 32. ' Fellow, Latin American Teaching Fellowship Program (Tufts University, USA), Centro de Pesquisas de Produtos Site A: Sdo Miguel Estate, Ceard-Mirim, Rio Grande do Norte A sugar cane field with numerous lateral drainage canals and a snail population that varied from 0 to 200 B. glabrata per m2 was selected for treatment. The granules were applied at 50 kg/ha, or twice the dose reported (Crossland, personal communication, 1971) to have given a 100% kill in laboratory tests. This corresponds to 0.2 g of active ingredient per M2. The product was scattered manually over standing water (maximum depth 30 cm, usual depth 2 cm), moist margins of the canals, and dried canals that might harbour aestivating snails. A total of 9 kg of granules was applied. A separate area with similar conditions was left untreated as a control. Observa- tions were made after 24 hours, 5 days, I month, and 2 months. Site B: Itaoca, Itapemirim, Espirito Santo A temporary pond with a surface area of 457 m2 was selected. The population of B. tenagophila had previously been recorded at over 1 000 snails per m2, but at the time of treatment, 5 weeks after the pond had almost completely dried up, it was less than 200 snails per M2. A total of 2 kg of formulation, or approximately 0.18 g of trifenmorph per m2, was applied with a Hatsuta Blowmic Am-8 portable mistblower equipped with a granule spreader and operated with the volume control at position 2. Naturais, ICB, Bloco H, Ilha do Fundao, Universidade Federal do Rio de Janeiro. a PAULINI, E. In: Controle ambiental da esquistossomose. Belo Horizonte, Centro de Engenharia Sanitaria, Escola de Engenharia, Universidade Federal de Minas Gerais, 1968. b This experimental formulation was provided by Shell Research Ltd, Woodstock Agricultural Research Centre, Sittingbourne, Kent, England. 3130 - 377- B. GILBERT ET AL. Granules reached all but a 1.5-m swath in the centre, where the water was 0.5 m deep. Observations were made after 3 days and monthly thereafter. Site C: Joao Ferreira Estate, Itapemirim, Espirito Santo A former marsh drained by over 700 m2 of canal and now used for field crops was selected. The water was 0-8 cm deep in lateral canals and 15-20 cm deep in the slowly flowing main canal; the pH was 5.6. Although there had previously been more than 100 B. tenagophila per m2 of surface in the main canal, because of a recent drought the population had fallen to about 1 snail per 6 M2. At the time of application adult snails, young snails, and egg masses were found. A total of 4 kg of granules-0.23 g of trifenmorph per m2-was applied with a Hatsuta Blowmic Am-8 portable mistblower in an attempt to eliminate the residual snail population. Observations were made after 3 days, 1 month, and 2 months. RESULTS At site A, almost complete mortality was achieved within 24 hours. Two surviving snails were found in one lateral canal. Sporadic death of the fry of small fish species was also observed initially. However, both medium-sized and small fish were observed alive in the treated area after 5 days, when the snail popula- tion had been eliminated. The site remained free of snails until the annual floods reintroduced B. glabrata Table 1. Reduction of snail population by application of trifenmorph granules at three field locations Reduction of population after various intervals (%)b Site a 1 3-5 1 2 5 day days month months months A 98 100 100 100 - c B - 98 100 100 100 C - 50 50 50 50 a The sites are described in the main text. b Estimated by comparing observed population with that present at time of application. Continued absence of snails implies not continued toxicity, but absence of repopulation. c Area flooded and repopulated from outside. 4 months later. At site B, only 6 snails were found 3 days after treatment. No snails were found during subsequent monthly readings. The site remained free of snails for 5 months, after which time B. tenagophila was intentionally reintroduced. At site C, trifen- morph eliminated all snails in the shallow stationary water of the lateral canals, but failed to reduce significantly the small number of snails found in the main canal. Small numbers of snails (< 1 per 12 M2) were found during each of the monthly observations. No phytotoxicity was observed at any of the sites. DISCUSSION Trifenmorph granules applied at 2 kg of active ingredient per ha were effective against B. glabrata and B. tenagophila in a drainage system and a temporary pond. The failure to provide complete control at a third site can probably be attributed to a combination of low pH and the presence of flowing water in the main canal. Snails were eliminated in the lateral canals holding stationary water, regardless of its pH. Granules are a desirable formulation. After the first rainfall, lasting 1 hour, a check at site A showed that the granules along canal margins and on dry canal beds were still intact 6 days after application. The eventual dissolution of these granules and de- layed release of trifenmorph into the water probably acts to eliminate snails that escape the initial applica- tion, such as those found in the first observations at sites A and B. The granules are convenient to use; they can be spread by hand with no equipment at all, and the use of portable mistblowers equipped with granule spreaders allows application at normal walk- ing pace. Site B was treated in less than 3 minutes. For larger sites a 2-man team is used: one operates the mistblower while the other keeps it refilled. Refilling is done without switching the machine off or removing it from the operator's back. Because water is not used as a diluent, the spray team is not exposed to infection while fetching water to prepare the formulation. Likewise, the spray tank does not become dirty during granule application and so does not need washing at the site. ACKNOWLEDGEMENTS This study was supported by the Conselho Nacional de Pesquisas, CAPES, the Conselho de Pesquisas da UFRJ, FNDCT contract No. CT 140, BNDE Funtec contract 167, and US Army grant No. DAHC 19-72-G-0015. Facilities for the work were provided by Dr J. Pellegrino (Universidade Federal de Minas Gerais, Belo Horizonte) in the state of Espirito Santo, and by Dr G. H. Aguirre and Dr Percilio A. de Oliveira, Instituto Nacional de Endemias Rurais, in Rio Grande do Norte. 378 MOLLUSCICIDAL ACTIVITY OF TRIFENMORPH 379 R1cSUMIt ACTIVITE MOLLUSCICIDE DU TRIPHENMORPHE LORS D'ESSAIS SUR LE TERRAIN Le triphenmorphe est un molluscicide efficace contre les espces de Biomphalaria qui transmettent la schisto- somiase. Pour pallier les inconv6nients r6sultant de son emploi sous forme de poudres mouillables ou de concen- tr6s pour 6mulsions, on a utilis6 des granules, contenant 4% de produit actif, appliques manuellement ou m6ca- niquement, ce qui 6vite le contact entre l'op6rateur et l'eau et elimine le risque d'infection. Le molluscicide a ete appliqu6 en trois endroits, a la dose approximative de 0,2 g de produit actif par m2. Cette dose, correspondant a 50 kg de granules par hec- tare, est deux fois plus forte que celle qui tue 100% des mollusques au laboratoire. Dans une plantation de cannes a sucre, a Rio Grande do Norte, on a obtenu en 24 heures l'6limination complete de B. glabrata qui s'est maintenue pendant 4 mois. Certains granules ont 6t6 retrouv6s intacts 6 jours apres l'application et la destruction totale du mollusque est peut-etre due a la lib6ration tardive d'une partie du produit actif. Les pois- sons de taille petite ou moyenne n'ont subi aucun dommage, mais on a observ6 sporadiquement la destruc- tion du frai au cours du Ier jour. Des r6sultats similaires ont ete obtenus dans un bassin temporaire, d'une super- ficie de 457 m', a Espirito Santo, oii B. tenagophila a Wt6 completement 6limin6 pour une dur6e de 5 mois. Par contre, dans un marais proche, on n'a pas reussi & d6truire completement cette espece, cet echec relatif 6tant attribue a 1'existence de courants et au faible pH(5,6) de l'eau. Les granules de triphenmorphe apparaissent donc comme une formulation convenant au traitement rapide et sans danger des eaux dormantes oi ils assurent la destruction a 100% des mollusques. REFERENCES 1. BOYCE, C. B. C. ET AL. Nature, 210: 1140 (1966). 2. CROSSLAND, N. 0. Eull. Wld Hlth Org., 37: 23 (1967). 3. BARBOSA, F. S. & BARBOSA, I. Ecology, 39: 763 (1958).