Research and on-farm demonstration activities have permitted growers to improve their programs and to respond to new threats. The identification and use of insecticides less toxic to natural enemies, particularly of leafminers, resulted in the conservation of these natural enemies and the fuller integration of biological control into the program. Sampling was improved using visual assessments for leafminer larvae and their parasites, yellow sticky traps for leafminer adults and pheromone traps for tomato pinworm adults. The development of the mating disruption technique for the tomato pinworm reduced the need for insecticides to control this pest. The technique is based upon the mass application of sex attractant pheromones to confuse males trying to locate females, with the result that mating success is reduced and fewer fertile eggs are deposited. New sampling procedures and action thresholds were developed for the pepper weevil on pepper. The role of nightshade weed hosts in the population dynamics of the pepper weevil led to cultural recommendations to manage these weeds during the summer off-season.
A
serious outbreak of the silverleaf whitefly in the late 1980s and early
1990s threatened to disrupt existing IPM programs, especially on tomato.
Growers increased insecticidal applica-tions to manage a
new irregular ripening disorder
and a new disorder called geminivirus, tomato mottle virus (ToMoV), that
research at GCREC linked with the whitefly. New research
efforts were undertaken
to counteract this threat. Efficacious insecticides were identified in
laboratory and field experiments, including evaluations on commercial
farms. Recent studies have demonstrated the potential of selected commercial
products and novel compounds
as repellents for
the silverleaf whitefly and may lead to new and less-disruptive whitefly
control.
The use of UV-reflective, polyethylene soil mulch for delaying and, thereby, reducing populations of the silverleaf whitefly and the incidence of ToMoV was pioneered at GCREC. Cooperative studies showed that most infection of plants with ToMoV in commercial tomato fields was accomplished by whitefly adults migrating into fields rather than by movement of whitefly adults within the field. Treating seedlings with plant growth promoting (PGPR) bacteria provided by colleagues at Auburn University reduced the population of the whitefly and delay incidence of geminivirus in the field. The potential of windbreaks such as sugar cane to impede between field movement of whitefly adults was suggested by an analysis by on-campus colleagues of population dynamics data on a mixed vegetable, organic farm. In a survey coordinated by GCREC, over 12 species of parasites and at least that number of predators were found to attack the silverleaf whitefly in Florida, the Caribbean and Central and South America. Studies on vegetables at an organic farm and on weeds on perimeters of tomato fields showed that these natural enemies could inflict up to 90-100% mortality of the whitefly in the absence of broad spectrum, conventional insecticides. Furthermore, the application of artificial honeydew, a mixture of sugar, whey and yeast, increased egg laying by lacewing predators, thereby further increasing the potential of biological control. Larvae of a native trash bearing lacewing species, i.e. one that glues the remnants of its prey on its body, was shown in laboratory studies to prefer whitefly nymphs to aphids, another common prey of lacewings. Improved methodology for rearing larvae of this lacewing in the laboratory was developed to enhance the potential for commercialization of the species. The trash bearing lacewing species was also shown in laboratory studies to be more tolerant of selected insecticides than a non-trash bearing species. Some insecticides were found to be biorational, that is, they were more toxic to the silverleaf whitefly than they were to the lacewing. The intraplant distribution of immature lifestages of the silverleaf whitefly on tomato plants was studied and found to correspond similarly to that of leafminers. Therefore, sampling of the two species was focused on the same site on the plant. Using this sampling site, studies showed that the severity of irregular ripening of tomato was related to numbers of whitefly nymphs. This information was then used to develop experimentally and then to demonstrate commercially an action threshold for applying insect growth regulators to manage the whitefly and avoid irregular ripening.
Several wild species of tomato were found to be nearly immune to attack by the silverleaf whitefly due to the presence of glandular hairs or trichomes. Cooperative studies have demonstrated the difficulty in transferring this resistance to cultivated tomato. Further cooperative studies were undertaken to identify resistance to ToMoV in wild tomato species. Progress has been made in transferring this resistance to cultivated tomato and there is likelihood of resistant germplasm being released.