The Practical Solutions in this section were carried under EMPHASIS’ project activities. Here you can review the short summary of the study, get acquainted with its main expectation and results and explore the main practical recommendations. The section provides answer to the questions What is the main added value/benefit/opportunities if the knowledge is implemented? How can a practitioner make use of the scientific results?
Bemisia tabaci is an obligate phloem-feeding pest, which is globally distributed. In total, at least 120 plant viruses are transmitted by B. tabaci, causing diseases of vegetable and fibre crops worldwide. Tomato (Lycopersicon esculentum) crops are particularly susceptible to more than 50 different species of the Begomovirus genus, including Tomato yellow leaf curl virus (TYLCV) and Tomato yellow leaf curl Sardinia virus (TYLCSV) both of which reduce yields and can cause large economic losses in tomatoes (Bedford et al., 1994). TLYCV and TYLCSV have been recorded in countries all around the Mediterranean Basin.
Because B. tabaci is acquiring resistance to pesticides and because of the retrieval of pesticides from the European market, the development of novel control methods for this pest based on biological control agents will benefit European agriculture.
Currently two predatory species are being used in the Mediterranean greenhouses: Macrolophus pygmaeus (commercially called Macrolophus caliginosus) and Nesidiocoris tenuis. The two species belong to the heteropteran family of Miridae and are omnivorous, that is, they can feed on both animal prey and plant materials. First species is very slow for establishing on the crop when it is released in the greenhouse whereas the second is quite fast but may strongly damage plant causing flower abortion, decrease of cosmetic value of fruit and reduced yield. For these reasons, new alternatives are needed.
EMPHASIS project aimed to provide greenhouse growers with new generalist predators that overcome the constraints of the two commercially available species, that is, M. pygmaeus (commercially called M. caliginosus) and N. tenuis.
Four main specific objectives were:
Two Dicyphus species have been tested, Dicyphus bolivari and Dicyphus errans. However, the protocol that follows refers only to D. bolivari, the one on which most applied results have been obtained in the EMPHASIS project.
Specific recommendations on biological control must be adapted to specific local conditions of the greenhouse, tomato variety, production area and crop season, among others. We recommend to consult the predator provider for adaptations of the following protocol to each tomato greenhouse.
In order to improve the early establishment of the predator on the crop, it is recommended to inoculate an initial population of the predator in the plant seedlings. A rate of 1 to 2 adult predators per plant are released in the nursery between 11-13 days before transplanting; Autumn season tomato should release closer to 2 adults/plant whereas for spring tomatoes about 1 adult/plant may be enough. With this schedule, most of individuals in the seedlings are at the egg stage when plants are transplanted into the greenhouse, and loss of mobile nymphs in the transplanting process is prevented. Two successive releases of alternative food, f.i. Ephestia kuehniella eggs (dose of 0.01-0.02 g/plant) are performed in the nursery in order to favour the establishment of the predators on the plants.
Once young plants have been transplanted into the greenhouse, it is required to monitor whitefly and predator populations. The number of whitefly adults and predator individuals on the 7 upper fully developed leaves will be scouted every 7-15 days (in warmer season/area – cooler season/area respectively). If the whitefly control exerted by the predator is not effective enough, an extra release of the predator should be done at a rate of 0.5-1 adult/plant. To maintain the predator on the plant, complementary predator food (Ephestia eggs) may be added to the crop at a rate of 10 grams per 1.000 individuals of D. bolivari released. A common procedure is the mixture of the eggs of Ephestia inside the bottles of D. bolivari, just before the release of the predators, so that the alternative food is provided together with the predatory populations.
Dicyphus bolivari will offer the same biological control protection when the greenhouse whitefly, T. vaporariorum, is infesting the crop, instead of or together with B. tabaci. It can also be expected a certain suppressing action of D. bolivari on other insect pests other than whiteflies, but D.bolivari can fail to suppress them at densities below economic threshold in case of high infestations. Then, other measures, including application of chemicals, are needed. In order to minimize chemical side effects on the predator in these situations, including the application of chemicals to control diseases, it is advisable to consult the predator provider about which active ingredients can be used and how can they be applied. Also, cultural practices have to be adapted to enhance predator action. For instance, plant deleafing must consider that D. bolivari adults and nymphs may be foraging on leaves below flower trust and their removal can affect predator abundance.
Dicyphus spp. are omnivorous predators, that is, under certain circumstances they can feed on the plants, including fruit and so they can cause some injuries on plants. In the case of D. bolivari, plant damage only occurs when there are high populations and the ratio predator/prey is too high. This is to say, when the action of the predator is ‘too good’ and the prey has been effectively suppressed. This situation, too many predators for low prey density, must be avoided and data of whitefly and predator monitoring can alert us about risks of plant damage. In such cases, a chemical spray to lower predator density is required. Consult the predator supplier (usually their webpages contain the information needed) in such cases.
Bedford, I.D. Briddon, R.W. Brown, J.K. Rosell, R.C. Markham, P.G.1994. Geminivirus transmission and biological characterisation of Bemisia tabaci (Gennadius) biotypes from different geographic regions. Ann. Appl. Biol., 125: 311-325