Journal of Insect Science (2008) 8 (4), 5-6
Judit Arnó, J. Roig and R. Gabarra (2008)
Bemisia tabaci biotype Q and its natural enemies in vegetable and ornamental crops
Journal of Insect Science 8 (4), 5-6
in P. A. Stansly and C.L. McKenzie, organizers: Fourth International Bemisia Workshop - International Whitefly Genomics Workshop, December 3-8, 2006, Duck Key, Florida, USA
Abstract: Vegetables in some Mediterranean areas are grown mainly on small family operated farms. Vegetable crops are grown year- round in open fields and greenhouses built with metal frames, covered with plastic films, and mostly unheated. Vegetable production coexists with ornamental crops either in the open field or in heated greenhouses. In this situation, whiteflies reproduce all year with continuous carry-over among different crops and environments. For many years, Trialeurodes vaporariorum has been one of the main pests. However, from the early 90's, populations of Bemisia tabaci have been increasing in vegetable and ornamental crops. In the area of study, the northeast of Spain, tomato, cucumber and poinsettia crops are often heavily infested by B. tabaci. This pest usually coexists with T. vaporariorum and their relative abundance changes with crop and season. Tomato is grown in three different crop cycles from February to December in greenhouse and outdoors. Cucumber is grown mainly in greenhouses in two crop cycles from March to November. Finally, poinsettia is grown for the Christmas market in heated greenhouses from July to December. In tomato, biological control of whiteflies, by conservation and augmentation of native populations of the mirid bug Macrolophus caliginosus, is used by many growers. In cucumber, no specific biological control program is applied and, although the crop is sprayed more often that tomato, natural enemies can be preserved to a certain extent. In poinsettia, releases of the parasitoid Eretmocerus mundus to control B. tabaci populations together with the use of soft insecticides began in 2003 in few farms as an alternative to chemical control of the pest. In this scenario, we wanted to determine the importance of three B. tabaci sensitive crops (tomato, cucumber and poinsettia) on the survival of this whitefly, and to evaluate the natural enemies associated with B. tabaci and T. vaporariorum. For this purpose, tomato crops (IPM and non IPM) were surveyed: 9 in spring, and 7 in autumn 2003, and 11 in spring and 17 in autumn 2004. We also surveyed 7 cucumber greenhouses during September 2004, 7 poinsettia greenhouses during 2003 and 5 more during 2004. In these poinsettia greenhouses, growers released Er. mundus combined with the use of soft insecticides. Thirty tomato leaflets, 30 cucumber leaf-disks (9.6 cm2), and 30 poinsettia leaves were sampled to evaluate B. tabaci infestation, parasitization and predation. Parasitized pupae were isolated until the emergence of the parasitoid to determine its species. In tomato, Trialeurodes vaporarioum was the predominant species in the spring crops whereas B. tabaci was the most abundant in autumn crops. In cucumber and poinsettia, B. tabaci was almost the only whitefly present. In autumn 2004, although the infestation was very different among greenhouses, average density of B. tabaci on cucumber (3.43 nymphs/ cm2) was significantly greater than on tomato (0.13 nymphs/ cm2) or poinsettia (0.08 nymphs/ cm2) (F= 43.7; df 2,28; P<0.000). These data showed that cucumber was the most important host where B. tabaci built up its population during autumn. Nevertheless, poinsettia allowed B. tabaci survivorship in cooler seasons because it was grown in heated greenhouses and could maintain whitefly populations until December. Parasitoids caused the greatest mortality of B. tabaci pupae in cucumber (average 18%), but their incidence in tomato was much lower (average 10%). Note that B. tabaci parasitoids had not been released neither in cucumber nor in tomato. On the other hand, in poinsettia, Er. mundus was released in most of the greenhouses, and parasitism was substantial (average 56%). Encarsia pergandiella and Er. mundus were found parasitizing B. tabaci pupae with Er. mundus comprising 49 and 58 % of all parasitoids emerging from tomato and cucumber, respectively. Yet, in tomato and cucumber, both species were seldom found together in the same greenhouse (just in 2 out of 21 samples). In contrast, during 2004, both En. pergandiella and Er. mundus were found together in all the poinsettia greenhouses. Probably, the inoculation of Er. mundus in those greenhouses forced the coexistence of both parasitoids. Predator species differed in all 3 crops. Predators were particularly important in tomato where M. caliginosus was the most abundant. In early tomato crops, where the B. tabaci population was very low, average predation reached 20 % of T. vaporariorum and 9% of B. tabaci nymphs. At the end of the season, percentages increased up to 34 and 46 % of T. vaporariorum of B. tabaci nymphs, respectively. In cucumber, average predation of nymphs was <1%. This mortality factor was not evaluated in poinsettia due to the low numbers of whitefly predators detected in the crop. In summary, the use of biological control in early tomato crops, where T. vaporariorum was the main whitefly species, conserved and enhanced M. caliginosus and En. pergandiella populations. Later on, these natural enemies caused a great deal of mortality in B. tabaci populations in the autumn crops. To reduce overall B. tabaci populations in the area, biological control of B. tabaci should focus on cucumber, since this crop hosts the highest B. tabaci populations. The high natural parasitism rates that we found in some cucumber greenhouses suggest that parasitoid releases could avoid the build up of the pest in this crop. In poinsettia, releases of Er. mundus were effective in some greenhouses and reduced dramatically B. tabaci populations. However, it would be necessary to maintain the heating until the end of the crop to be able to sustain high levels of parasitism.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Database assignments for author(s): Judit Arnó, Rosa Gabarra
Research topic(s) for pests/diseases/weeds:
biocontrol - natural enemies
surveys/sampling/distribution
Research topic(s) for beneficials or antagonists:
surveys/distribution/isolation
