Toxicity of natural and synthetic sugar esters against tobacco insects with an emphasis on the tobacco aphid, Myzus nicotianae Blackman, (Homoptera: Aphididae)

This research focused on the evaluation of natural sugar esters from Nicotiana spp. and synthetic sucrose esters against the tobacco aphid. Natural sugar esters (SE) from wild tobacco, Nicotiana gossei Domin, were highly toxic to the tobacco aphid, Myzus nicotianae Blackman, in laboratory evaluations. LC{dollar}sb{lcub}50{rcub}{dollar} values for N. gossei SE against immature and apterous adult tobacco aphids of the red color form were 0.38 and 0.59 mg/ml using a leaf spray technique, and 0.55 and 0.92 mg/ml using a slide dip technique, respectively. The toxicities of N. gossei SE to the red and to the green color forms of the tobacco aphid were not significantly different. Aphid toxicity from N. gossei SE was much lower in the field than it was in the laboratory. N. gossei SE were not toxic to other major insect pests and predators on tobacco.; Aphid mortality from a rate of 1 mg/ml of N. gossei SE was more than 5-fold higher under moist conditions than dry conditions in laboratory bioassays. A positive linear relationship was shown between aphid mortality from N. gossei SE and relative humidity.; Toxicity of all types of SE and sucrose esters tested to tobacco aphids was significantly improved by certain humectants. Improved efficacy was related to the type and concentration of the humectants and SE. The addition of a 5% of concentration of certain humectants to a 1 mg/ml solution of N. gossei SE resulted in {dollar}>{dollar}90% aphid mortality in the laboratory, compared with 12.4% aphid mortality from SE alone. Increased efficacy from the addition of humectants was lower in field tests than in laboratory tests.; Four synthetic analogs of natural N. gossei sucrose esters demonstrated toxicity to the tobacco aphid in laboratory tests. It appeared that octanoyl sucrose esters were the most toxic to aphids, and decanoyl sucrose esters were the least toxic. The efficacy of synthetic sucrose esters in fields were erratic and appeared to be related to application volume, the type of foliage coverage, and relative humidity.