Balsam fir (Abies balsamea) needles and their essential oil kill overwintering ticks (Ixodes scapularis) at cold temperatures

Abstract

The blacklegged tick, Ixodes scapularis, vectors Borrelia burgdorferi, a bacterium that causes Lyme Disease. Although synthetic pesticides can reduce tick numbers, there are concerns about their potential effects on beneficial insects, such as pollinators. Plant-based pest control agents such as essential oils could provide an alternative because they have low environmental persistency; however, these products struggle to provide effective control. We found a new natural acaricide, balsam fir (Abies balsamea) needles, that kill overwintering I. scapularis ticks. We extracted the essential oil from the needles, analyzed its chemical composition, and tested it for acaricidal activity. We placed ticks in tubes with substrate and positioned the tubes either in the field or in incubators simulating winter temperatures. We added balsam fir essential oil, or one of the main components of balsam fir essential oil (i.e., ß-pinene), to each tube. We found that both the oil and ß-pinene kill overwintering ticks. Whole balsam fir needles require several weeks to kill overwintering ticks, while the essential oil is lethal within days at low temperatures (≤ 4 °C). Further, low temperatures increased the efficacy of this volatile essential oil. Higher temperatures (i.e., 20 °C) reduce the acaricidal effectiveness of the essential oil by 50% at 0.1% v/v. Low temperatures may promote the effectiveness of other natural control products. Winter is an overlooked season for tick control and should be explored as a possible time for the application of low toxicity products for successful tick management.

Figure 1

Effect of intact and ground balsam fir needles on the survival of adult female Ixodes scapularis exposed to 0–4 °C. N = 27 ticks/group for Week 1 and Week 3. For Week 2, N = 36 for controls and N = 45 for intact or ground balsam fir needles (BF Needles—intact balsam fir needles, Ground BF—ground balsam fir needles).

Figure 2

Ground balsam fir needles, ß-pinene and balsam fir essential oil kill ticks at two different temperatures (0 °C and 12 °C). Bars represent the percentage of dead ticks after 4 weeks. BF = Balsam Fir, BF EO = Balsam Fir Essential Oils. Control N = 24/incubator, Ground BF N = 16/incubator, ß-pinene N = 24/incubator, BF EO N = 32/incubator.

Figure 3

Mean repellency (%) over time of Ixodes scapularis nymphs exposed to balsam fir essential oil (EO) at different concentrations (1–8% v/v). N = 30 per treatment.

Figure 4

Balsam fir essential oil killed ticks at a lower concentration at 2 °C than at 20 °C. The black bars represent the mortality at 2 °C while the grey bars represent mortality at 20 °C. N = 32 for each bar except N = 36 at 0%.