Effects of two commercial neem-based insecticides on lone star tick, Amblyomma americanum (L.) (Acari: Ixodidae): deterrence, mortality, and reproduction

Authors: Showler, Allan; Osbrink, Weste; MORRIS, JAY - University Of Texas Health Science Center; WARGOVICH, MICHAEL - University Of Texas Health Science Center

Submitted to: Biopesticides International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2017
Publication Date: 8/2/2017
Citation: Showler, A., Osbrink, W.L., Morris, J., Wargovich, M. 2017. Effects of two commercial neem-based insecticides on lone star tick, Amblyomma americanum (L.) (Acari: Ixodidae): deterrence, mortality, and reproduction. Biopesticides International. 13:1-12.

Interpretive Summary: The lone star tick is a widely distributed obligate blood-feeding parasite in the United States and Mexico. It mostly attaches to white-tailed deer and wild turkey, but also to other animals, including humans. Some diseases such as erhlichiosis and tularemia can be transmitted by the pest. Two commercial neem-based products for home garden use, Neemix (a viscous liquid) and AzaSol (a powder), containing 4.5% and 6% azadirachtin, respectively, as the labeled active ingredient, were assessed for effects against different life stages of the tick. We determined that Neemix also contained high concentrations of three additional bioactive compounds: nimbolide, nimbin, and salannin. When doses of azadirachtin were approximately the same, the two neem-based formulations caused similar contact mortality against larvae. High doses of Neemix induced complete mortality from volatiles when larvae and adults were exposed, apparently caused by non-azadirachtin compounds. Neem-based products can induce multiple bioactive effects that differ from other neem-based products because the products might be comprised of different bioactive constituents and because the products might have the same constituents but in substantially different amounts. Only Neemix was repellent against larvae, which might have resulted from the presence of the bioactive compounds other than azadirachtin. Growth regulator and sublethal effects on egg laying and egg hatchability were not observed.

Technical Abstract: The lone star tick, Amblyomma americanum (L.), is a widely distributed three-host obligate blood-feeding parasite in the United States and Mexico. It mostly attaches to white-tailed deer, Odocoilus virginianus (Zimmerman) and wild turkey, Meleagris gallopavo L., as well as a wide variety of other domestic and wild hosts such as cattle, dogs, horses, goats, quail, squirrels, opossums, hares, coyotes, and humans. Diseases known to be transmitted by A. americanum include erhlichiosis, rickettsiosis, tularemia, and protozoan infections. Two commercial neem-based products registered for home garden use, Neemix (a viscous liquid) and AzaSol (a powder), containing 4.5% and 6% azadirachtin (a limonoid), respectively, as the labeled active ingredient, were assessed for contact toxicity, lethal effects of volatiles, repellency, and sublethal effects on egg laying and hatching. We determined that Neemix also contained high concentrations of three additional bioactive limonoids: nimbolide, nimbin, and salannin. When doses of azadirachtin were approximately the same, the two neem-based formulations caused similar contact mortality against larvae. High doses of Neemix induced complete mortality from volatiles when larvae and adults were exposed and non-azadirachtin compounds appeared to be the cause. Neem-based products can induce multiple bioactive effects that differ from other neem-based products because the products might be comprised of different bioactive constituents and because the products might have the same constituents but in substantially different amounts. Only Neemix was repellent against larvae, which might have resulted from the presence of the bioactive compounds other than azadirachtin. Growth regulator and sublethal effects on egg laying and egg hatchability were not observed. The feasibility of protecting hosts against A. americanum using the neem-based products is discussed.