Dermanyssus gallinae

Soulié, Anne-Sophie, Sleeckx, Nathalie & Review, Lise Roy, 2021, Repellent properties of natural substances against Dermanyssus gallinae: review of knowledge and prospects for Integrated Pest Management, Acarologia 61 (1), pp. 3-19 : 10-11

5 Factors modulating the repellent activity of natural substances against D. gallinae

5.1 Physiological status of mites

The mite’s physiological status may have an impact on the host searching behavior. Visser

(1988) highlighted that starved and satiated phytophagous insects did not behave similarly in terms of seeking host plants. In D. gallinae the behavioral response to a substance detected by olfaction might vary according to the time since the last blood meal. To date, the effect of this factor has been tested on the toxic effects of essential oils on D. gallinae (more toxic as the time since the last blood meal increases, George et al. 2008), but not with regard to repellency. Testing the variation in behavioral response to repellent substances as a function of the physiological status of D. gallinae can allow a better understanding of the chemical interactions between D. gallinae and its environment.

5.2 Concentrations and ratios of compounds

The effect induced by a compound depends on its concentration and the duration of exposure to the mite ( Deletre et al. 2016). Nechita et al. (2015) showed that the repellent effect of thyme essential oil decreases concomitantly with increasing dilution. Lee et al. (2019) studied the repellent effects of cinnamon bark oil, clove bud oil and their volatile organic compounds depending on the evaporation time. They showed that both of the essential oils are repellent regardless of evaporation time. However, two components of clove bud oil, eugenol and eugenol acetate, were found to change from having a repellent to an attractant effect over time in the experiment. The authors proposed that this may be partly explained by a difference in the dynamics of evaporation between the single compounds and the whole essential oil. Furthermore, Barimani et al. (2016) conducted a study to determine whether, and at what concentration, carvacrol, a compound known to be toxic to several arthropod pests (Ahn et al.

1998), can generate a toxic effect without being overly repellent. The aim was to implement a control strategy involving a trap containing carvacrol at toxic, but non­repellent levels. Whilst traps containing 1% and 2% of carvacrol had a similar toxicity to mites, the former trapped more mites than the latter over two weeks.

Combinations of compounds and their ratios have an impact on compounds repellency against various arthropods ( Deletre et al. 2016). Carvacrol­thymol combinations that differed with their ratio were tested against D. gallinae by Masoumi et al. (2016). Both thymol and carvacrol were significantly repellent alone and the combination of these two molecules had a synergistic effect for acaricidal purposes. However, no such synergy was observed when considering repellency ( Masoumi et al. 2016). In short, the available studies on the effect of concentration and ratios of repellent substances against D. gallinae are limited and have only focused on four compounds (eugenol, eugenol acetate, carvacrol and thymol) and two essential oils (clove bud oil and thyme essential oil).

5.3 Ambient factors

Several studies have reported an impact of the humidity level on the olfactory capacities of certain insects, particularly Anopheles gambiae ( Takken, Knols and Otten 1997) and Ostrinia nubilalis ( Royer and McNeil 1993) . Thus far, a single study has been carried out on the repellency caused by substances not derived from plants D in. gallinae , the entomopathogenic fungus Beauveria bassiana ( Kilpinen and Steenberg 2016) . Kilpinen and Steenberg (2016) tested the repellent activity (undifferentiated category) against D. gallinae produced by this biological agent using an experimental device that allowed the mite to come into contact with the conidia at two different relative humidity levels, alone or in combination with a desiccant inert dust. Addition of desiccant dust to the conidia significantly increased the repellency exerted by B. bassian a. Furthermore, the repellent effect of the fungi­dust combination was significantly higher at 85% than at 75% relative humidity ( Kilpinen and Steenberg 2016).

Many other factors can influence the repellency of substances used against D. gallinae in poultry houses: e.g., the often fine and abundant dust present can buffer volatile compounds and compounds emitted from manure (e.g., NH 3), and/or the nature of the materials composing the building structure can interfere with some repellents (volatile molecules can be more or less fixed on surfaces depending on the material). We have not found any studies that specifically test these interactions. In addition, decomposition activity by microorganisms can interfere in a relatively unpredictable way, e.g., feathers that have remained in the litter for some time are more attractant to D. gallinae than fresh feathers ( Koenraadt and Dicke 2010). It is important to keep in mind that, partly because of these diverse factors with unknown effects, results from laboratory experiments may not always transfer well to the field.