|The impact of quinea export on peasant's livelihoods of Bolivian highlands
Laguna, P. - \ 2000
In: X World Congres of the International Rural Sociology Association, Rio de Janeiro : July 30-August 5, 2000. - Brazil : [s.n.], 2000. - Published on CD-rom
|Heterogeneidad, cultura, impacto, acción individual y colectiva : por un nuevo enfoque en el estudio de las organizaciones económicas campesinas bolivianes
Laguna, P. - \ 1999
In: Sociólogos en el umbral del Siglo XXI : II Congreso Nacional de Sociologia, La Paz, 1999 / G. Danilo Paz, R. Sandoval, S. León, P. Romero, M.I. Pérez (eds). - [S.l.] : Colegio de Sociólogos de Bolivia, 1999. - ISBN 84-89891-53-2 - p. 211 - 233.
Population dynamics of rice leaffolders(Lepidoptera: Pyralidae) and their natural enemies in irrigated rice in the Philippines
Kraker, J. de; Huis, A. van; Heong, K.L. ; Lenteren, J.C. van; Rabbinge, R. - \ 1999
Bulletin of Entomological Research 89 (1999)5. - ISSN 0007-4853 - p. 411 - 421.
Populations of rice leaffolders and their natural enemies were studied in eight crops of irrigated rice in Laguna Province, the Philippines. The rice leaffolder complex consisted of three species: Cnaphalocrocis medinalis (Guenée), Marasmia patnalis Bradley and M. exigua Butler. Leaffolder population dynamics were characterized by an egg peak at maximum tillering and a broad larval peak around booting stage. Peak densities ranged from 0.2 to 2.0 larvae per hill. Most larvae originated from immigrant moths and there was no substantial second generation. The seasonal percentage egg parasitism by Trichogramma sp. ranged from 0 to 27°and percentage larval parasitism from 14 to 56ÐThe braconid Macrocentrus philippinensis Ashmead was the most commonly reared larval parasitoid. Forty natural enemy taxa that may attack rice leaffolders were identified from suction and sweepnet samples: 24 predator taxa and 16 parasitoid taxa. The estimated survival rates from leaffolder egg to larval stages and between larval stages showed large variation between rice crops, but were not clearly correlated with observed levels of parasitism, natural enemy abundance, or natural enemy to leaffolder ratios. It is suggested that the generally low densities of rice leaffolders in Philippine transplanted rice are caused by their ovipositional preference for crops at the maximum tillering stage, allowing for only one generation, and by high immature mortality caused by the abundant and diverse complex of natural enemies.
|Egg mortality of rice leaffolders Cnaphalocrocis medinalis and Marasmia patnalis in irrigated rice fields
Kraker, J. de; Huis, A. van; Lenteren, J.C. van; Heong, K.L. ; Rabbinge, R. - \ 1999
Biocontrol Science and Technology 44 (1999)4. - ISSN 0958-3157 - p. 451 - 473.
Egg mortality of rice leaf folders Cnaphalocrocis medinalisand Marasmia patnalis was studied in unsprayed irrigated rice fields in Laguna Province, the Philippines. Mortality was assessed by field exposure of laboratory-laid eggs for two days and by monitoring of field-laid eggs. Egg disappearance, the major mortality factor, was low in the first four weeks after transplanting and then increased. Egg parasitism by Trichogrammajaponicum was highest at the start of the crop and decreased to a low level towards crop maturity. Non-hatching of eggs was of minor importance. Over the total duration of the egg stage, the average disappearance of exposed laboratory-laid eggs was40%, and of field-laid eggs 46%. Egg mortality due to parasitism averaged 15% and 18%, respectively. The potential impact of egg parasitism is probably partly obscured by the disappearance of parasitized eggs. Mortality rates were highly variable between egg cohorts, but with multiple regression analysis several factors were identified that statistically explained a significant part of this variation. The results suggest that the predatory crickets Metiochevittaticollis and Anaxipha longipennis play a major role in egg disappearance, and that egg parasitism is positively dependent on the overall density of host eggs of Trichogramma in the field.
|Impact of UV-radiation on plankton in an arctic freshwater lagoon (Brandal Laguna, Spitsbergen).
Donk, E. van; Lange, H.J. de; Faafeng, B.A. - \ 1998
In: SIL XXVII Congress, Dublin, Ireland (1998)
|Users' Perspectives: Literature Review on the Development of a Concept. UPWARD,.
Hardon-Baars, A. - \ 1997
Unknown Publisher - 46 p.
|User/use-oriented approaches to technology assessment and innovation: some lessons for marketing research.
Hardon-Baars, A. - \ 1996
In: Into action research: partnership in Asian rootcrop research and development - p. 203 - 216.