Effects of the plant growth stimulant SBPI on Bemisia tabaci Genn . ( Homoptera : Aleyrodidae )

The environmentally friendly plant growth stimulant and pesticide SB Plant Invigorator (SBPI, Stan Brouard Group) helps the plant to produce quality fruit. Three days after tomato plants were sprayed for the first time with SBPI (2 mL L solution), this product seemed to be ineffective against Bemisia tabaci adults, as the numbers of dead females were practically equal on control and treated plants. After 3 days oviposition values on control plants did not differ significantly from those on treated plants. However, 31 days after the first treatment with weekly repeated treatments, new adult whiteflies started to emerge from pupae on control plants, but no L3, L4 or new adults were found on SBPI-treated plants. However, differences in the number of 1 + 2 instar larvae were not statistically significant. From these findings it can be concluded that, under these conditions, SBPI is an effective alternative product for the control of B. tabaci on tomato plants, as foliar application inhibits larval development decreasing the risk of a new whitefly generation. Additional key words: development, horticultural crops, reproduction, sweet potato whitefly, tomato.

reported in different agricultural systems worldwide (Denholm et al., 1998;Dennehy et al., 1999;Nauen and Denholm, 2005).Moreover, many of these products are toxic to the environment if they are not properly used.These disadvantages make necessary to carry out investigations on alternative strategies for the control of this species in the framework of IPM programmes.Utilization of new products, which fight pest physically but not chemically, are some of the alternative methods currently being investigated.
The SB Plant Invigorator (SBPI) developed by the Stan Brouard Group (Stan Brouard, 2005) has a physical mode of action that makes the product environmentally friendly.In 2005 the European Commission accepted SB Plant Invigorator as having a physical mode of action and it thus falls outside their pesticide directive 91/414/EEC (EWSN, 2005).Consequently SB Plant Invigorator is now available for use in many of the European member state countries without the requirement for registration.Due to its formulation, SBPI is a plant stimulant, and it has proved to be not toxic and environmentally safe.Therefore no harvest interval is required after it is used and special health and safety measures for users are not necessary.Further it does not cause residue problems in food (Stan Brouard, 2005).As its activity against insects is achieved by physical means, insects do not develop resistance to SBPI.This means that this product, even after long periods of application continues to be useful.The objective of this study was to analyze if SBPI was effective for the control of B. tabaci in commercial tomato plants.
Seeds of tomato (Lycopersicon esculentum Miller) cv.Marmande were germinated in a climate chamber maintained at 24ºC, 60% r.h. and a photoperiod of 16:8 (L:D).Plants were grown in red sand for the 10 first days and then in vermiculite.They were grown in 500 mL plastic pots and irrigated every other week with a nutrition complex at a concentration of 3 g L -1 (Nutrichem 60; Miller Chemical, Hanover, PA).Twenty 47-day-old plants were used for the assay.
Ten plants were sprayed using a small plastic spray with SBPI (2 mL L -1 ) 12 times per plant, twice per six leaves.The rest of the plants were free water sprayed following the same proportions.To determine the effect of the product on different developmental stages of B. tabaci, and following the manufacturer's directions, the treatment was repeated weekly for the following 4 weeks (Stan Brouard, 2005).All treated and control plants were whitefly infested 1 1 /2 h after the first treatment with SBPI product or water.Five female adults of B. tabaci (B-biotype) were removed from a colony reared on tomato plants cv.Marmande, and placed into each of 10 clip-cages per assay (one cage per plant) attached to the under surface of one leaf (Nombela et al., 2001).Whiteflies were removed after 3 days, and eggs and dead individuals counted.First + second instar larvae, 3 rd and 4 th instar larvae and adults were recorded 31 days after initial treatment.
Data were analyzed with a one-way ANOVA followed by Tukey's HSD test (StatSoft, 1994).
The mean number of eggs and dead adults on control and treated plants did not differ significantly and this trend continued for 1 st + 2 nd instar larvae (Table 1).The lower number of 1 st + 2 nd instar larvae in control plants could be due to some immature insects developing to the next stage in the SBPI-treated plants but they died, and therefore, their development stopped at the 2 nd instar stage, so no 3 rd and 4 th instar larvae or adults were recorded on these plants.
Recent studies on the mode of action of the product as a whitefly pesticide have shown that SBPI causes adult whitefly to stick to a wet layer that this product forms on the leaves where whiteflies land on them.Adult whiteflies produce a white wax powder that causes the white colour of their wings.Close examination showed that this wax powder becomes sticky when it is mixed with SBPI (Stan Brouard, 2005).This may explain why adult whiteflies are trapped by their wings after plant treatment and the insects remain stuck although the surface dries, and they die (Stan Brouard, 2005).However, there was no evidence of this in the present study as the number of dead adults was practically equal in both control and treated plants.The present results also showed that 3 rd and 4 th instar larvae were controlled by SBPI but in a different way to the adults.Whitefly larvae have a coating of wax that protects them form rainwater.
The SBPI overcomes this protection and causes the larvae to suffocate.This physical mode of action does not allow B. tabaci to develop resistance and this makes the products useful for long term use.From these findings it can be concluded that SBPI can reduce the use of toxic pesticides for the control of B. tabaci in commercial tomato plants.

Table 1 .
Mean (± SE) numbers of B. tabaci dead females and eggs after 3 days and different instar larvae and empty pupal cases after 31 days in control (water) and treated (SBPI) plants Means followed by the same letter in the same clumn do not differ significantly (P < 0.05) by the Tukey's HSD test.