ImergardTMWP: A Non-Chemical Alternative for an Indoor Residual Spray, Effective against Pyrethroid-Resistant Anopheles gambiae (s.l.) in Africa

Use of diatomaceous earth to control nymphal American dog ticks, Dermacentor variabilis Say (Acari: Ixodidae): laboratory to simulated field experiments

Diatomaceous earth (DE) recently was shown to rapidly kill ticks. Proof of concept for use of DE to kill the American dog tick, Dermacentor variabilis, the most widely distributed native three-host tick in North America, has not been investigated. Unfed D. variabilis nymphs dipped into DE and incubated at 30 °C and 50 versus 70% relative humidity (RH) had an estimated median survival time of 5 h and 4 h, respectively, with mortality starting within 1 h. There was no difference in survival time at the 50 and 70% RH. In a two-choice assay at 30 °C and 50% RH, ticks walked freely onto DE treated surfaces; the estimated median survival time was 3 h, indicating that DE is not a repellent. There was no difference in locomotor activity between DE-treated nymphs and untreated controls. In simulated-field experiments, pine straw infested with nymphs and then treated with DE at 5.00, 2.50, 1.25, 0.63 and 0.31 g DE/m2 resulted in 100% mortality and 81.40% (± 4.13%) mortality at 0.15 g DE/m2 after 24 h. Scanning electron microscopy of the dead ticks in the 0.15 g DE/m2 treatments showed most of the cuticle surface was devoid of DE except for the hypostome. The rapid time to first death by dipping, the no effect of RH on survival time, the small amounts of mineral on the tick body and no visible scarring on the tick cuticle questions the generally accepted mode of action for DE, that is, cuticle damage and dehydration.

Non-Chemical Control of Nymphal Longhorned Tick, Haemaphysalis longicornis Neumann 1901 (Acari: Ixodidae), Using Diatomaceous Earth

The longhorned tick (LHT), Haemaphysalis longicornis Neumann (Acari: Ixodidae), is a serious invasive pest in North America where its geographical range is expanding with high densities associated with commercial animal production. There are only a few chemical pesticides available for LHT control, which can lead to the evolution of resistant strains. Diatomaceous earth (DE) was shown to be effective in killing some important tick species but was not examined for LHTs. When LHT nymphs were dipped for about 2-4 s into DE, transferred to Petri dishes (one tick/dish), and incubated at 30 °C and 70% relative humidity, the median survival time was 4.5 h. A locomotor activity assay showed that there was no difference in the overall distance traveled between the DE-treated and control ticks except during the first 2 h after exposure. In a field-simulated study in which a dose of 5.0 g DE/m2 was applied to pine needle litter infested with LHT, all the LHTs were dead at 24 h with no control mortality. Scanning electron micrographs showed the mineral adhering to all surfaces of the tick. The results indicated that DE is effective in killing nymphal LHTs and could be an alternative to the use of chemical acaricides with the advantage of managing pesticide resistance through the killing by a different mode of action and could be used for organically certified animal husbandry.

Malaria vector control in sub-Saharan Africa: complex trade-offs to combat the growing threat of insecticide resistance

Mass distribution of insecticide-treated nets (ITNs) has been a key factor in reducing malaria cases and deaths in sub-Saharan Africa. A shortcoming has been the over-reliance on pyrethroid insecticides, with more than 2·13 billion pyrethroid ITNs (PY ITNs) distributed in the past two decades, leading to widespread pyrethroid resistance. Progressive changes are occurring, with increased deployment of more effective pyrethroid-chlorfenapyr (PY-CFP) or pyrethroid-piperonyl butoxide (PY-PBO) ITNs in areas of pyrethroid resistance. In 2023, PY-PBO ITNs accounted for 58% of all ITNs shipped to sub-Saharan Africa. PY-PBO and PY-CFP ITNs are 30-37% more expensive than standard PY ITNs, equating to an additional US$132-159 million required per year in sub-Saharan Africa to fund the shift to more effective ITNs. Several countries are withdrawing or scaling back indoor residual spraying (IRS) programmes to cover the shortfall, which is reflected by the number of structures sprayed by the US President's Malaria Initiative decreasing by 30% from 5·67 million (2021) to 3·96 million (2023). Benin, located in West Africa, is a prime example of a country that ceased IRS in 2021 after 14 years of annual spraying. Our economic evaluation indicates that IRS in Benin cost $3·50 per person protected per year, around five times more per person protected per year compared with PY-PBO ($0·73) or PY-CFP ITNs ($0·76). Although costly to implement, a major advantage of IRS is the portfolio of at least three chemical classes for prospective resistance management. With loss of synergy to PBO developing rapidly, there is the danger of over-reliance on PY-CFP ITNs. As gains in global malaria control continue to reverse each year, current WHO projections estimate that key 2030 malaria incidence milestones will be missed by a staggering 89%. This Personal View explores contemporary malaria vector control trends in sub-Saharan Africa and cost implications for improved disease control and resistance management.

Biomolecular Minerals and Volcanic Glass Bio-Mimics to Control Adult Sand Flies, the Vector of Human Leishmania Protozoan Parasites

Sand flies (Diptera: Psychodidae) serve as vectors for transmitting protozoan parasites, Leishmania spp., that cause the disease called leishmaniasis. The main approach to controlling sand flies is the use of chemical insecticides. The discovery of alternative methods for their control is needed because of potential health risks of chemical insecticides and development of sand fly resistance to these pesticides. The biomineral produced by diatoms (diatomaceous earth, DE; Celite) and a volcanic glass bio-mimic (Imergard) have been shown by our group to be efficacious against mosquitoes, filth flies, and ticks but never studied for the control of sand flies. In a modified World Health Organization cone test, 50% of adult Phlebotomus papatasi sand flies at 29 ± 1 °C, 55 ± 5% RH, and 12:12 LD, when exposed to Imergard and Celite, were dead in 13.08 and 7.57 h, respectively. Proof of concept was established for the use of these biominerals for sand fly and leishmaniasis disease control. Using a light source as an attractant to the minerals had no significant effect on the LT50, the time to 50% mortality. The LT50 at a higher relative humidity of 70 ± 5% increased to 20.91 and 20.56 h for Imergard and Celite, respectively, suggesting their mode of action was dehydration. Scanning electron microscopy of dead sand flies showed high coating levels of Celite only on the sides of the thorax and on the tarsi, suggesting an alternative mode of action for mechanical insecticides.

Acaricidal Biominerals and Mode-of-Action Studies against Adult Blacklegged Ticks, Ixodes scapularis

Ticks in the USA are the most important arthropod vector of microbes that cause human and animal disease. The blacklegged tick, Ixodes scapularis, the focus of this study, is able to transmit the bacteria that causes Lyme disease in humans in the USA. The main approach to tick control is the use of chemical acaricides and repellents, but known and potential tick resistance to these chemicals requires the discovery of new methods of control. Volcanic glass, Imergard, was recently developed to mimic the insecticide mode of action of the minerals from diatoms (diatomaceous earth, DE) for the control of malaria mosquitoes in Africa. However, studies on the use of these minerals for tick control are minimal. In a dipping assay, which was put into DE (Celite), the times of 50 and 90% death of adult female I. scapularis were 7.3 and 10.5 h, respectively. Our mimic of DE, Imergard, killed ticks in 6.7 and 11.2 h, respectively. In a choice-mortality assay, ticks moved onto a treated surface of Imergard and died at 11.2 and 15.8 h, respectively. Ticks had greater locomotor activity before death when treated by dipping for both Imergard and Celite versus the no-mineral control. The ticks after making contact with Imergard had the mineral covering most of their body surface shown by scanning electron microscopy with evidence of Imergard inside their respiratory system. Although the assumed mode of action of Imergard and Celite is dehydration, the minerals are not hygroscopic, there was no evidence of cuticle damage, and death occurred in as little as 2 h, suggesting minimal abrasive action of the cuticle. Semi-field and field studies are needed in the future to examine the practical use of Imergard and Celite for tick control, and studies need to examine their effect on tick breathing and respiratory retention of water.

Mechanical Acaricides Active against the Blacklegged Tick, Ixodes scapularis

Cases of Lyme disease in humans are on the rise in the United States and Canada. The vector of the bacteria that causes this disease is the blacklegged tick, Ixodes scapularis. Current control methods for I. scapularis mainly involve chemical acaricides. Unfortunately, ticks are developing resistance to these chemicals, and more and more, the public prefers non-toxic alternatives to chemical pesticides. We discovered that volcanic glass, ImergardTM WP, and other industrial minerals such as Celite 610 were efficacious mechanical insecticides against mosquitoes, filth flies, and agricultural pests. In this report, when 6-10- and 50-70-day old unfed I. scapularis nymphs were dipped for 1-2 s into Celite, the time to 50% mortality (LT50) was 66.8 and 81.7 min, respectively, at 30 °C and 50% relative humidity (RH). The LT50 was actually shorter at a higher 70% RH, 43.8 min. Scanning electron microscopy showed that the ticks were coated over most of their body surface, including partial to almost total coverage of the opening to their respiratory system. The other mechanical insecticide, Imergard, had similar efficacy against blacklegged unfed nymphs with an LT50 at 30 °C and 50% RH of 70.4 min. Although more research is needed, this study suggests that industrial minerals could be used as an alternative to chemical pesticides to control ticks and Lyme disease.

New thinking for filth fly control: residual, non-chemical wall spray from volcanic glass

Filth flies are of medical and veterinary importance because of the transfer of disease organisms to animals and humans. The traditional control methods include the use of chemical insecticides. A novel mechanical insecticide made from volcanic glass and originally developed to control mosquitoes (Imergard™ WP; ImG) was investigated for control of adult grey flesh flies, Sarcophaga bullata (Parker), secondary screwworms, Cochliomyia macellaria (F.), and house flies, Musca domestica L. In a modified WHO cone test device, the time to 50% mortality (LT₅₀ ) when applied at 5 g/m² (tested at 30 °C and 50% relative humidity (rH)) was 7.1, 4.3 and 3.2 h, respectively. When knockdown was included, the LT₅₀ s were 5.5, 1.5 and 2.8 h, respectively. Application rates of 1.25 and greater g/m² had the shortest LT₅₀ s. The time to the LT₅₀ increased for M. domestica as rH increased, but ImG was still active at the highest rH tested of 70%. Scanning electron micrographs showed ImG was present on all body parts, unlike that for mosquitoes where it was found mostly on the lower legs. These first studies on the use of Imergard WP against flies suggest this could be an alternative method for filth fly control.

Bio-Efficacy of Diatomaceous Earth, Household Soaps, and Neem Oil against Spodoptera frugiperda (Lepidoptera: Noctuidae) Larvae in Benin

Spodoptera frugiperda was first reported in Africa in 2016 and has since become a serious threat to maize/cereal production on the continent. Current control of the pest relies on synthetic chemical insecticides, which can negatively impact the environment and promote the development of resistance when used indiscriminately. Therefore, great attention is being paid to the development of safer alternatives. In this study, several biorational products and a semi-synthetic insecticide were evaluated. Two household soaps ("Palmida" and "Koto") and a detergent ("So Klin") were first tested for their efficacy against the larvae under laboratory conditions. Then, the efficacy of the most effective soap was evaluated in field conditions, along with PlantNeem (neem oil), Dezone (diatomaceous earth), and Emacot 19 EC (emamectin benzoate), in two districts, N'Dali and Adjohoun, located, respectively, in northern and southern Benin. The soaps and the detergent were highly toxic t second-instar larvae with 24 h lethal concentrations (LC50) of 0.46%, 0.44%, and 0.37% for So Klin, Koto, and Palmida, respectively. In field conditions, the biorational insecticides produced similar or better control than Emacot 19 EC. However, the highest maize grain yields of 7387 and 5308 kg/ha were recorded, respectively, with Dezone (N'Dali) and Emacot 19 EC (Adjohoun). A cost-benefit analysis showed that, compared to an untreated control, profits increased by up to 90% with the biorational insecticides and 166% with Emacot 19 EC. Therefore, the use of Palmida soap at 0.5% concentration, neem oil at 4.5 L/ha, and Dezone at 7.5 kg/ha could provide an effective, environmentally friendly, and sustainable management of S. frugiperda in maize.