## 4 Discussion  
The results showed that the foliar spray with increased water volume improved the _B. tabaci_ control. Although the exact reason for this result is unclear, it is most likely due to improved spray coverage on the foliage or improved translaminar movement when using a nozzle tip that discharged more insecticide solution than the nozzle tip that discharged less insecticide solution. This is especially important for _B. tabaci_ control, as they colonize the abaxial side of the leaves. Previously, many studies showed a similar result when systemic insecticides were tested against many piercing-sucking and some chewing insect pests. When a greater spray volume of acetamiprid was applied against citrus mealybug, _Planococcus citri_ ([PERSON]), it caused >70% mortality than at lower volumes [31]. [PERSON] et al. [32] showed the improved efficacy of imidalcoprid + lambda-cyhalothrin applied at a greater spray volume (>16.8 L/ha) using an unmanned aerial vehicle against wheat aphid, _Riopalosiphum padi_ ([PERSON]) than that applied at lower volumes. The efficacy of spirotetramat against Asian citrus pysllid, _Diaplorina citri_ [PERSON], and citrus leafminer, _Phyllocnistis citrella_ [PERSON], improved when the spray volume was increased regardless of application methods, such as airblast or Proptec rotary atomizer sprayers [33]. The densities of the Western transirished plant bug, _Lygus heserus_ [PERSON], were significantly reduced when sulfoxaflor was applied at a greater spray volume using an electrostatic sprayer [29]. These studies showed that increasing the spray volume of systemic insecticides can improve pest control. Figure 4: All instars of _B. tabaci_ (mean (\(\pm\)SE)) observed on poinsettia leaves treated on insecticide–method combination treatments compared with nontreated check treatment in the greenhouse at (**A**) 7, (**B**) 14, (**C**) 21 and (**D**) 28 days after application. The asterisks (*) indicate the significant difference between specific insecticide–method combination treatment and nontreated check treatment (Student’s \(t\)-test; \(\alpha\) = 0.05). Previous studies reported that dinotefuran is more toxic to _B. tabaci_ than other neocitoinoids, such as imidalcoprid and thiamethoxam [34; 35], and also when applied as a soil drench [11]. Additionally, the soil drench application of dinotefuran was effective in controlling other piercing-sucking insects, such as hemlock woolly adelgid, _Adgeles tsugae_ ([PERSON]) [36], and _Bagrada hilaris_ ([PERSON]) [37]. In the current study, however, the soil drench application failed to deliver adequate _B. tabaci_ control using dinotefuran. It is unclear why the drench application did not provide acceptable _B. tabaci_ control. One reason could be the high water volume (7483.2 L/ha) used for drench application in the current study. The water volume used in the commercial container plants varies by the insecticide product (as specified in the label) and container volume. Perhaps, the water volume used for drench application in the current study excessively diluted the concentration of active ingredients in the solution. For example, the water volume used by [PERSON] and [PERSON] [11] for drench application of dinotefuran was 935.4 L/ha, which was eight times lower than what was used in the current study. Some growers use high water volume for insecticide spray for better coverage and efficacy (S.V.J., personal communications). In addition, the dinotefuran product used in [PERSON] and [PERSON] [11] contained 20% of dinotefuran (Safari(r) 20 SG, Valent USA, Walnut Creek, CA, USA), whereas the product (Zylam) used in the current study had only 10% of dinotefuran. The spinetoram + sulfoxaflor (XXpire) provided reasonable _B. tabaci_ control when applied as a high spray volume (spench) than foliar or drench applications. Spinetoram component of XXpire is active on insects mostly by contact or ingestion of residues [38], which is a less probable exposure route on nymphs of _B. tabaci_ infested on poinsettia.