Lethal Effects of a Silica Gel + Pyrethrins (Drione) on Amblyomma americanum (Ixodida: Ixodidae) Larvae and Nymphs.

Ixodids (hard ticks) ingest blood from host animals, and they can transmit pathogenic organisms that induce medical and veterinary diseases. As resistance to synthetic conventional acaricides becomes more common, alternative tactics are coming under heightened scrutiny. Laboratory bioassays were used to assess the efficacy of CimeXa, a commercially available silica gel desiccant dust product, and Drione, a commercial product containing silica gel + pyrethrins and a synergist, piperonyl butoxide, against lone star tick, Amblyomma americanum (L.) (Ixodida: Ixodidae), larvae and nymphs. Both life stages were completely killed by CimeXa by 24 h, and Drione caused total larval mortality within 1 h when they were briefly immersed in the dusts and when they crawled across dust-treated substrate; nymphs were completely killed by 4 h after the same kinds of exposure. Mortality of A. americanum larvae and nymphs occurred after the pests crawled across dried aqueous suspensions of the products, but this was not as efficient and fast-acting as when the immature life stages were exposed to dry dusts. Further, dried aqueous suspensions of Drione were not substantially more lethal than dried aqueous suspensions of CimeXa. CimeXa and Drione will provide prophylactic control on vegetation and animals for as long as the silica gel remains without being physically removed. Both of the dust-based products will likely also be effective against other problematic ixodid species. Advantages and disadvantages, and potential uses, of desiccant dust-based acaricides are discussed.

Lethal Effects of a Commercial Diatomaceous Earth Dust Product on Amblyomma americanum (Ixodida: Ixodidae) Larvae and Nymphs.

With increasing development of resistance to conventional synthetic acaricides in economically and medically important ixodid species, interest in finding alternative control tactics has intensified. Laboratory bioassays were conducted, using the lone star tick, Amblyomma americanum (L.), as a model species, to assess the efficacy of a diatomaceous earth-based product, Deadzone, in comparison with a silica gel-based product, CimeXa. CimeXa is already known to be highly lethal against A. americanum larvae and nymphs. The two dust treatments were 100% effective against larvae and nymphs within 24 h after contact occurred by immersion in dry dusts and after crawling across a surface treated with the dry dusts. Contact by crawling on a dried aqueous film of the dusts, even at a concentration of 10%, was not as effective as exposure to the dusts in dry powder form. As has been demonstrated with CimeXa, it is likely that Deadzone will be capable of providing prophylactic protection of cattle from economically important one-host ixodids, such as the southern cattle fever tick, Rhipicephalus microplus (Canestrini), which vectors the causal agents of babesiosis. Diatomaceous earth can be stored indefinitely, will remain efficacious for as long as sufficient quantities remain on the substrate, it is a natural (organic) substance, and it might be amenable for limited use in environmentally protected habitats.

Lethal Effects of a Silica Gel + Thyme Oil (EcoVia) Dust and Aqueous Suspensions on Amblyomma americanum (Ixodida: Ixodidae) Larvae and Nymphs.

Ixodids suck blood from host animals and transmit pathogens that cause important medical and veterinary diseases. As synthetic conventional acaricide resistance becomes increasingly common, alternative tactics are likely to enhance control efforts. Laboratory bioassays assessed the lethality of CimeXa, a commercial silica gel desiccant dust, and EcoVia, a commercial product containing silica gel + thyme oil, against lone star tick, Amblyomma americanum (L.), larvae and nymphs. Both life stages were completely killed by CimeXa by 24 h, and EcoVia achieved total larval mortality within 1 h when they were initially immersed in the dusts and when they crawled across treated substrate. Larvae were killed faster than nymphs. Temporary immersion of A. americanum larvae and nymphs in aqueous suspensions of the dusts were less effective than exposure to the dusts applied dry. Larval and nymphal mortality associated with crawling on dried aqueous suspensions of the products was also not as strong as when the immature life stages crawled across substrate treated with dry dusts, and EcoVia was not more efficient than CimeXa. CimeXa and EcoVia can likely be used to protect cattle in a prophylactic context because silica gel does not degrade, and EcoVia might be effective at eliminating ticks that are feeding on cattle as well. We suggest that the two dust products be assessed for efficacy against other ixodid species, such as the southern cattle fever tick, Rhipicephalus microplus (Canestrini), which transmits the causal agents of babesiosis to cattle.

Effects of Formic Acid on Amblyomma americanum (Ixodida: Ixodidae) Larvae and Nymphs.

Ixodids are blood-feeding ectoparasitic vectors of many disease agents that infect humans, livestock, and wild animals. As ixodid resistance to conventional synthetic acaricides becomes increasingly problematic, natural products are receiving greater attention as possible alternative control tactics. Formic acid, produced by ants, is a commercially available product for fumigating varroa mites, Varroa destructor Anderson & Trueman, infesting honey bee, Apis mellifera L., hives, and it has been reported to repel ixodids. Lone star tick, Amblyomma americanum (L.), larvae and nymphs were used as a model ixodid to investigate deterrent, repellent, and lethal effects of formic acid as a fumigant and contact toxin in vitro in the laboratory. Although formic acid failed to deter or repel A. americanum, it was highly toxic as a fumigant to larvae at a 1% concentration even when exposure was limited to 5 min. Contact by crawling on wet, moist, and dry treated substrates under ventilated conditions causes >90% mortality to larvae in 5% formic acid concentration treatments within 30-120 min, and temporary immersion killed ≈60% of the larvae by 24 h after they were removed from the 5% formic acid treatment solution. Substantial nymphal mortality occurred after 1-1.5 h following exposure to substrate treated with the 10% concentration and immersion killed ≈45% of the nymphs. It appears that formic acid volatiles are more lethal to A. americanum immatures than direct contact with the external integument.

Metastriate Ixodid Life Stages Protected from Predatory Ants in Texas.

Multiple predatory ant species, including the red imported fire ant, Solenopsis invicta (Buren) (Hymenoptera: Formicidae), have been reported to attack ixodids (Ixodida: Ixodidae), but evidence has largely been circumstantial. When living lone star tick, Amblyomma americanum (L.) (Acarina: Ixodidae), eggs, and unfed and blood-engorged larvae, nymphs, and adults were deployed on bait transects with hot dog slices and dead house flies, Musca domestica L., in West, Central, and South Texas. The various ixodid life stages were not attacked while ants were strongly recruited to the hot dog and M. domestica baits. Similarly, when the same ixodid life stages and other baits were placed adjacent to colonies of two ant species (red harvester ant, Pogonomyrmex barbatus (Smith) and the red imported fire ant, Solenopsis invicta Buren) the ixodids were not preyed upon while hot dog slices and dead M. domestica were immediately attacked. Some ant species dragged blood-engorged adult ixodids and eggs away from the colony entrance, where they were originally placed, and discarded them. Evidence and mechanisms for allomone-based ant deterrence in the genera Amblyomma, Dermacentor, and Rhipicephalus (metastriate ixodids) are discussed. Protection of ixodids from predatory ants helps to explain why metastriate ixodids remain problematic worldwide despite the presence of predaceous ants.

Lethal Effects of Silica Gel-Based CimeXa and Kaolin-Based Surround Dusts Against Ixodid (Acari: Ixodidae) Eggs, Larvae, and Nymphs.

As tick resistance to conventional acaricides becomes more common, alternative control tactics are gaining attention. Insecticidal dusts CimeXa and Surround, based on silica gel and kaolin, respectively, were assessed against Amblyomma americanum (L.) (Ixodida: Ixodidae) eggs, larvae, and nymphs in the laboratory. Coverage by the dry dusts, particularly CimeXa, was strongly lethal to larvae and to a lesser extent to nymphs. Larval mortality was also high when larvae crawled across thin layers of CimeXa and, to a lesser extent, Surround dusts. CimeXa was more lethal to nymphs that crawled across a thin layer than Surround. Larval mortality after crawling on dried aqueous suspensions of the dusts for 30 min and for 48 h caused moderate mortality (<80%) regardless of a 10-fold difference in concentration; nymphal mortality was negligible. In a field experiment, CimeXa dust strongly reduced numbers of Gulf coast tick, Amblyomma maculatum (Koch) (Ixodida: Ixodidae), larvae and nymphs by 24 h. Possible application of CimeXa to control other species of ixodid ticks is discussed as well as advantages and disadvantages of using dusts for tick control under field conditions.