EN QUOI L'ETUDE DE L'EPIDEMIOLOGIE DES MALADIES A BEGOMOVIRUS DE LA TOMATE PEUT-ELLE AIDER A LA CONCEPTION DE SYSTEMES DE CULTURE INNOVANTS ?

In the late 1980's, a new biotype of the whitefly Bemisia tabaci and associated begomoviruses appeared in the Caribbean particularly on tomato crops. The propagation of these diseases was supported by the intensification in vegetable cropping systems. The use of insecticides is not efficient, and no resistant varieties are available for these regions. The challenge is to develop integrated pest management packages, adapted to the different contexts. In order to identify the key-factors of the epidemics, we carried out surveys in tomato producing areas. On the other hand, we monitored the begomovirus inoculum pressure and vector populations, we prospected among weeds as virus reservoirs and we evaluated the effect of cultural practices on the disease progress. The survey underlined the great diversity of cultural practices, and revealed some factors linked with low disease incidences : presence of physical barriers, and presence of plants non-hosts of the vectors close to the plots. Tomato is the only reservoir of tomato begomoviruses and the vectors feed mainly on vegetable crops. The epidemic risk is high from March to September and the proximity with an infected plot as well as a high inoculum pressure during the first 3 weeks of culture can cause severe epidemics. Barriers around a plot may delay the epidemic process and reduce the incidence only when vector population level is low. Actually, the control of the disease must be laid on the spatial and temporal management of plots and the elimination of begomovirus sources. The acceptability of these practices needs the demonstration of their impact and a certain level of organisation of the growers for their application

Insect-screened cultivation to reduce the invasion of tomato crops by Bemisia tabaci: modelling the impact on virus disease and vector

1: In two experiments carried out in Guadeloupe, barriers were used to reduce the entry of the virus vector Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) to tomato plots. The barriers erected around the crop were of insect-proof cloth fences (<50 mesh), 1.5 m in height, in the first experiment with a deltamethrin-treated, insect-attracting strip facing inwards, and, in the second, with the barrier but no insecticide-treated strip. 2: A mathematical model of epidemic development was fitted to the symptom data from the treated and control (unprotected) tomato plots. There were two viruses present, tomato yellow leaf curl and potato yellow mosaic; specific detection confirmed that symptoms gave an accurate indication of infection and that the two virus diseases had similar progress curves. 3: Parameter estimates obtained by model-fitting suggested that the barriers reduced vector immigration by approximately 12-fold but that B. tabaci retention within the plots was also increased slightly despite the mortality caused by the insecticide-treated strips. Disease establishment was delayed by approximately 2 weeks. The results obtained in the second experiment involving barriers deployed without insecticide-treated strips could be explained by a large increase in B. tabaci retention within the barriers resulting in more rapid virus disease progress than in controls. The results of mathematical modelling indicate that partial insect barriers can be worse than none because sufficient whiteflies can enter to establish a population and, at the same time, large numbers are retained in the barrier plot, with the net effect being a more rapid population increase than in the absence of barriers

EN QUOI L'ETUDE DE L'EPIDEMIOLOGIE DES MALADIES A BEGOMOVIRUS DE LA TOMATE PEUT-ELLE AIDER A LA CONCEPTION DE SYSTEMES DE CULTURE INNOVANTS ?

In the late 1980's, a new biotype of the whitefly Bemisia tabaci and associated begomoviruses appeared in the Caribbean particularly on tomato crops. The propagation of these diseases was supported by the intensification in vegetable cropping systems. The use of insecticides is not efficient, and no resistant varieties are available for these regions. The challenge is to develop integrated pest management packages, adapted to the different contexts. In order to identify the key-factors of the epidemics, we carried out surveys in tomato producing areas. On the other hand, we monitored the begomovirus inoculum pressure and vector populations, we prospected among weeds as virus reservoirs and we evaluated the effect of cultural practices on the disease progress. The survey underlined the great diversity of cultural practices, and revealed some factors linked with low disease incidences : presence of physical barriers, and presence of plants non-hosts of the vectors close to the plots. Tomato is the only reservoir of tomato begomoviruses and the vectors feed mainly on vegetable crops. The epidemic risk is high from March to September and the proximity with an infected plot as well as a high inoculum pressure during the first 3 weeks of culture can cause severe epidemics. Barriers around a plot may delay the epidemic process and reduce the incidence only when vector population level is low. Actually, the control of the disease must be laid on the spatial and temporal management of plots and the elimination of begomovirus sources. The acceptability of these practices needs the demonstration of their impact and a certain level of organisation of the growers for their application