Insights on the activity of insecticides on major tomato pests: Tuta absoluta and Bemisia tabaci

Bemisia tabaci (Genadius) and Tuta absoluta (Meyrick) are considered the most important pests of tomato crops worldwide. Control of both insects can be problematic and substantial crop losses have been reported the past years.  Pest management for greenhouse tomato in Greece mainly relays on insecticides, since adoption of IPM based on beneficials is currently limited (> 20% of the total greenhouse tomato production). In this study the effects of insecticides on various developmental stages of T. absoluta and B. tabaci were investigated in an attempt to accurately evaluate the overall effect of insecticide treatments on the pest status.

The insecticides emamectin benzoate (14) , clorantraniliprole (35), flubendiamide (60), metaflumizone (240), spinosad (120), indoxacarb (70), chlorpyriphos (2400) and cypermethrin (50) were tested on T. absoluta; in parenthesis the respective maximum recommended field rate in mgL^-1 (RFRm). Larvicide activity (2^nd instar larvae) at the RFRm was high (>80%) in all cases expect for metaflumizone, chlorpyriphos and cypermethrin where moderate to low activity was detected (<80% mortality). True ovicide activity was not detected in most cases and only spinosad exhibited over 50% egg mortally at the RFRm. Activity of insecticides on the emerging first instars was similar to that exhibited to the 2^ndinstar larvae. Adulticide activity was evaluated using a method described for the first time in this study. Spinosad, chlorpyriphos and emamectin benzoate exhibited high activity on adults, with mortality being over 80%  5 days after treatment, while indoxacarb and  clorantraniliprole exhibited over 50% adult mortality at the  same interval (all % mortalities estimated at RFRm).

Flonicamid is novel systemic insecticide that acts as a feeding blocker and could serve as an excellent IPM tool for a pest with significant resistance management issues. Currently its efficacy on whiteflies and B. tabaci (MED) in particular, has not been investigated. Flonicamid exhibited low to no insecticidal activity on eggs, emerging crawlers and 2^nd instar larvae at the RFRm (125 mgL^-1). Adulticide activity was evaluated on B. tabaci using an original approach. Flonicamid was slow acting but efficient and exhibited >95% adult mortality at RFRm 10 days after treatment. Also it was observed that flonicamid applied at the RFRm significantly delayed the nymphal development (P>0.05). When it was applied systemically 50% of the larvae reached adult stage (DT₅₀) with a 2.9 day delay compared to control and for DT₉₀ a 10 day delay was observed. When applied via direct contact DT₅₀ was increased by 6.8 days and DT₉₀ was increased by >16 days compared to control. This effect has not been previously described for flonicamid. In long term cage experiments flonicamid applied at the RFRm restricted population development for one generation (approximately 32 days).