Impact of NeemAzal® on survival and reproduction of the biting louse Damalinia limbata on Angora goats

Secondary metabolites present in leaves and other plant parts have been demonstrated to exhibit various biological effects on phytophagous insect populations reducing their developmental, survival and reproductive rate. The neem tree (Azadirachta indica A. Juss, Meliaceae) contains at least 35 biologically active principles, among which, azadirachtin, a tetranortriterpenoid is the most prominent and active compound. Thus far, relatively few studies have been undertaken to assess the potential of neem products as insecticides for the control of ectoparasites on domestic animals. This study was conducted to characterize the effects of NeemAzal® (Trifolio M gmbH, Lahnau, Germany) on the biting louse Damalinia limbata (Phtiraptera) which is commonly found in Angora goats and to which quantitative and qualitative losses in fibre production are attributed. The experimentation was conducted on 47 Angora goats (Maridiana farm, Umbria Region) composed of 27 females and 20 males of varying age (0,5 – 5 years). All animals were naturally infested with D. limbata. Goats, divided in sex-matched groups of 11-12 individuals were treated by spraying with NeemAzal® containing azadirachtin at a concentration of 650 ppm or 125 ppm. Neguvon® was used as conventional treatment reference and 1 group was included as untreated control. During experimentation the goats were kept in two flocks, separated by sex but not by treatment. Louse counts were effected before treatment and after treatment on day 4, day 13 and then in monthly intervals. On each goat adult lice and nymphs were counted in 6 fleece partings of 1 cm x 10 cm on the upper and lower shoulder, rump and basin respectively. Egg development was evaluated in female lice collected from NeemAzal® treated and untreated goats by microscopic examination of dissected ovaries. Louse counts conducted on the 47 goats before treatment revealed a geometric mean parasite density of 118 (CI 91-153) lice per 60 cm2, corresponding to a mean burden of about 20,000 ectoparasites per animal. The intensity of infection varied considerably between goats ranging from 3-340 lice / 60 cm2. A relatively higher adult density was found on the ventral body area (72% of total adults, CI 67-77) whereas nymphs seemed to prefer the upper body region (61% of nymphs, CI 56-66). Nymphs accounted for 59% (CI 53-64) of the louse population. Two weeks after neem treatment louse burdens were decreased by 84% and 71% on goats sprayed with NeemAzal® at azadirachtin concentrations of 650 ppm and 125 ppm respectively (both p < 0.001). On goats belonging to the Neguvon® group a 98% reduction was recorded 4 days after treatment (p < 0.001), however louse populations approached control levels already 2 months later. At this time point on animals treated with NeemAzal® louse densities were still reduced by 96% and 92% in the 650 and 125 ppm group respectively (both p < 0.001) and in the 650 ppm group a 87% reduction could be observed up to 4 months after treatment (p < 0.001). Little variation of nymph proportions was recorded between NeemAzal® and control groups after treatment, indicating that the survival of both stages was reduced similarly by the neem product. Moreover, oviposition was found to be impaired: louse females (n=60) collected from neem treated goats and kept in laboratory for 1 week laid considerably less eggs (14) than control females (41 eggs; 2 =24.5, p<10-4 ). The dissection of ovaries revealed an impact on egg development involving all stages of oogenesis. Ovaries from neem exposed females harboured less frequently a mature egg (12/62) compared to controls (35/57; 2 =22.0, p<10-4 ). In addition, a high proportion of neem exposed ovaries displayed altered ovariole morphology (41/61). Frequently a loss of tissue and cell structure was observed and the fact that yolk spheres were rare in vitellogenic follicles suggests that neem compounds interfere with the process of vitellogenesis. The results of this study demonstrate the potential of neem products for the control of biting lice on fibre animals. Current? investigations focalize on evaluating the performance of a spot-on formulation of NeemAzal® on louse control and fibre production parameters.