Effectiveness and chemical composition of plant based acaricides against the two spotted spider mite Tteranychus urticae Koch (Acari : Tetranychidae)

Since 20 years, the development of integrated pest management (IPM) strategies is increasing since many problems appeared with the use of synthetic pesticides. Plant extracts are more and more considered within IPM strategies as alternative or complementary approach to insecticide treatments. Many plant essential oils show a broad spectrum of activity against pests. In this PhD thesis, I investigated the acaricidal effects of four plant extracts: Deverra scoparia Coss & Durieu (Araliales: Apiaceae), Santolina africana Jord & Fourr (Asterales: Asteraceae), Hertia cheirifolia Kuntze (Asterales: Asteraceae) and Allium sativum Linn. (Asparagales: Alliaceae) collected from Tunisia on the mite Tetranychus urticae Koch (Acari: Tetranychidae), one of the most serious phytophagous pests in the world. In the first step, the mortality and fecundity of female mites were measured upon treatment with an increase of the concentrations of essential oils with a potter spray tower. Mite mortality increased with oil concentration, with LC50 values ranging from 1.8 to 7.5 mg/l for all extracts. A reduction of the fecundity was already observed at lower concentrations ranging from 0.07 to 0.74 mg/l for all extracts. For a comprehensive evaluation of the potential of these four plant extracts as acaricides, they were characterized by GC, GC/MS and HPLC in order to analyse their chemical composition. Afterwards, I evaluated the acaricidal properties of the major components to identify the compounds conferring the biological activities against T. urticae. In a next step, artificial blends of components of the three essential oils were also prepared and tested with individual components missing from the mixture. The results showed that the presence of all constituents was necessary to equal the toxicity of the three natural oils. I analysed the persistence of acaricidal activity of these four extracts. Results showed that S. africana oil is the most persistent extract; D. scoparia oil is the less persistent. The combination of essential oils with a non-ionic surfactant (Tween 20), which is known as a binder, significantly increased the persistence of the biological activity of all extracts that lasts 10 days. Moreover, the combination with Tween increased significantly the differences between the plant extracts. Finally, I analyzed the resistance developped by the use of these 4 natural extracts. The treatment of S. africana did not induce any resistance while a low development of resistance was observed with H. cheirifolia, A. sativum and D. scoparia. In conclusion, compared to synthetic acaricides, the efficacy of these extracts against the two spotted spider mite is significantly higher with lower LC50 values, and higher decrease of the fertility. Moreover, the possibility to control the persistence and the slow development of resistance make them promising for pest management.Le développement des stratégies de lutte intégrée est en croissance depuis que de nombreux problèmes sont apparus suite à l’utilisation abusive et non raisonnée des pesticides de synthèse. Les extraits de plantes sont de plus en plus considérés, au sein des stratégies de lutte intégrée, comme des approches alternatives ou complémentaires aux traitements insecticides. Beaucoup d'huiles végétales essentielles montrent un large spectre d'activité contre les ravageurs. Durant cette thèse, nous avons étudié les effets de quatre extraits végétaux: Deverra scoparia Coss & Durieu (Araliales: Apiaceae), Santolina africana Jord & Fourr (Asterales: Asteraceae), Hertia cheirifolia Kuntze (Asterales: Asteraceae) et Allium sativum Linn. (Asparagales: Alliaceae) collectés en Tunisie, sur Tetranychus urticae Koch (Acari : Tetranycidae), l'un des ravageurs les plus graves dans le monde. En premier lieu, la mortalité et la fécondité des femelles ont été mesurés après traitement avec des concentrations croissantes d'huiles essentielles. La mortalité augmente avec l’augmentation des concentrations des extraits de plantes, avec des valeurs de LC50 allant de 1,79 à 7,49 mg/l. Pour toutes les huiles, une réduction de la fécondité a été observée à des concentrations de 0,07 à 0.74 mg/l. Ensuite, les huiles essentielles de D. scoparia, H. cheirifolia et S. africana et le distillat d'ail ont été caractérisées par GC, GC / MS et HPLC afin d'analyser leur composition chimique. Les propriétés acaricides des constituants les plus importants ont été étudiées. Troisièmement, les mélanges artificiels des constituants des trois huiles essentielles ont également été préparés et testés avec différents constituants manquants à partir du mélange. Les résultats ont montré que la présence de tous les constituants est nécessaire pour la toxicité des trois huiles naturelles. Enfin, nous avons analysé la persistance de l'activité acaricide de ces quatre extraits et leur résistance envers le tétranyque à deux points T. urticae. Les résultats ont montré que l’huile essentielle de S. africana est le plus persistent, par contre l’huile essentielle de D. scoparia est le moins persistent. La combinaison d'huiles essentielles avec un surfactant (Tween 20) augmente considérablement la persistance de l'activité biologique de tous les extraits durant 10 jours. Par ailleurs, la combinaison des extraits avec le Tween augmente les différences de rémanence entre les différents extraits. Le traitement par S. africana ne montre aucune résistance tandis qu'un faible développement de la résistance a été observée avec H. cheirifolia, A. sativum et D. scoparia. En conclusion, ce travail a démontré l'efficacité de ces extraits contre les tétranyques à deux points. Comparés aux acaricides de synthèse, les extraits de plantes sont efficaces, avec une faible concentration de CL50 et une diminution de la fécondité chez la femelle. De plus, la possibilité de contrôler leur persistance et le fait qu’ils induisent peu de résistance confirment leur valeur qu’outil efficace pouvant être utilisés dans une lutte intégrée contre les ravageurs.(AGRO 3) -- UCL, 201

Insecticidal activity of Lavandula angustifolia Mill against the pea aphid Acyrthosiphon pisum

The essential oil of Lavandula angustifolia was investigated for its biocide activity against Acyrthosiphon pisum by fumigation. The oil was characterised by GC-MS revealing that linalool was the most abundant component (38.57%), followed by linalyl acetate (29.95%), 1,8-cineole (13,66%), camphor (13,13%), - pinene (3,14%) and terpinene-4-ol (1,54%). The Mortality was measured upon treatment with oil concentrations ranging from 5 to 25 μl.l-1 of air. The mortality of aphids increased with oil concentration and LC50 values were determined to be 11.2 μl.l-1 of air. The full mixture was also prepared and toxicity was compared with individual constituents. The results showed that the presence of all constituents were necessary to equal the toxicity of the natural oil. L. angustifolia oil can provide valuable pesticide activity with significantly lower LC50 values

Insecticidal activity of Lavandula angustifolia Mill. against the pea aphid Acyrtosiphum pisum

peer reviewedThe essential oil of Lavandula angustifolia was investigated for its biocide activity against Acyrtosiphum pisum by fumigation. The oil was characterised by GC-MS revealing that linalool was the most abundant component (38.57%), followed by linalyl acetate (29.95%), 1,8-cineole (13,66%), camphor (13,13%), -pinene (3,14%) and terpinene-4-ol (1,54%). The Mortality was measured upon treatment with oil concentrations ranging from 5 to 25 µl.l-1 of air. The mortality of aphids increased with oil concentration and LC50 values were determined to be 11.2 µl.l-1 of air. The full mixture was also prepared and toxicity was compared with individual constituents. The results showed that the presence of all constituents were necessary to equal the toxicity of the natural oils L. angustifolia oil can provide valuable pesticide activity with significantly lower LC50 value

Assessment of the acaricidal activity of several plant extracts on the phytophagous mite Tetranychus urticae (Tetranychidae) in Tunisian citrus orchards

peer reviewedTo develop sustainable pest control in Tunisian citrus orchards, the present work aimed to evalute the toxicity of 31 plant extracts obtained from Tunisia and two synthetic acaricides (spirodiclofen and fenbutatin oxide) on the phytophagous mite species Tetranychus urticae (Koch)

Contrôle de Tetranychus urticae par les extraits de plantes en vergers d'agrumes

Tetranychus urticae est un acarien extrêmement polyphage, reconnu comme un ravageur majeur pour une grande quantité de plantes cultivées. Cet acarien cause d’importants dégâts sur agrumes et principalement sur citronnier, se traduisant par de lourdes pertes économiques. L’objectif de ce travail est de mettre en évidence les propriétés acaricides d'extraits de plantes sur T. urticae. Douze extraits (macérats) issus de 12 plantes et deux acaricides de synthèse (Spirodiclofen et Fenbutatin oxyde) ont été choisis pour les essais en verger de citronniers. Ces résultats montrent que trois macérats extraits d’Allium sativum, A. cepa et Deverra scoparia présentent des propriétés acaricides comparables aux deux acaricides de synthèse qui sont les produits de référence. Cette efficacité perdure jusqu’à plus de 15 jours. Le macérat de D. scoparia a présenté l’activité acaricide la plus toxique et la plus rapide sur la population de T. urticae, 21 jours après traitement par rapport aux autres extraits et par rapport aux produits de référence. Ce travail permettra de mettre en place un programme de lutte intégrée visant le contrôle efficace des tétranyques s’attaquant aux citronniers. Les expériences en verger ont démontré que les extraits végétaux ont un effet acaricide pour T.urticae

An analysis of potential resistance of the phytophagous mite, Tetranychus urticae Koch (Acari: Tetranychidae) to four botanical pesticides

Description of the subject. Synthetic acaricides have been widely used to manage Tetranychus urticae. Due to the excessive use of biocide and the associated problems of pesticide resistance and environmental pollution, there is an increasing demand for sustainable, environmentally-friendly control methods. Among the current alternative strategies aimed at decreasing the pest populations, the pesticides based on plant extracts are currently one of the most promising methods. Essential oils with acaricidal properties have been categorized as green pesticides because they are biodegradable and predominantly non-toxic to vertebrates. Objectives. With an aim to reduce the use of synthetic pesticides, they represent a promising approach for eco-chemical control of mites. Method. The aim of the present work was to analyze the risk of resistance emergence of T. urticae to repeated treatments with four plant extracts: Deverra scoparia Coss. & Durieu (Araliales: Apiaceae), Hertia cheirifolia (L.) Kuntze (Asterales: Ateraceae), Santolina africana Jord. & Fourr. (Asterales: Asteraceae) essential oils and garlic distillate Allium sativum L. (Asparagales: Alliaceae) after 20 generations. Results. Repeated treatments with S. africana essential oil during 20 generations did not provoke an emergence of resistance while a low development of resistance was observed with H. cheirifolia, A. sativum and D. scoparia extracts. Conclusions. The efficacy of these extracts against the two spotted spider mite and their low development of resistance make them a promising use for pest management

Persistence of toxicity in four natural extracts controlling Tetranychus urticae as affected by Tween®20 supply

Natural plant extracts are considered as promising tools to fight pests such as phytophagous mites and particularly against Tetranychus urticae that causes damage of economic importance in agriculture. The aim of the present work was to analyze the persistence of their biocidal activity and to investigate the possibility of extending their activities against T. urticae. Three essential oils from Deverra scoparia, Hertia cheirifolia and Santolina africana, and one distillate from Allium sativum are effective in controlling the two spotted spider mite T. urticae. The persistence of the plant extracts was evaluated and compared with and without a non-ionic surfactant composed of monosorbitanoleate (Tween®20). Without Tween®20 and five days following treatment, the four extracts rapidly lost their toxicity against T. urticae indicating low persistence of their biological activity. With Tween®20, their persistence significantly increased and lasted 10 days. The combination with Tween®20 significantly increased the differences between the respective persistence of the four plant extracts with S. africana being the most persistent extract and D. scoparia the less persistent. Even if possessing a high toxicity against T. urticae, natural plant extracts have only a poor persistence of their toxic effect. The enhancement of their efficacy and the increase of their persistence achieved by the use of Tween®20 make them a promising tool for pest management of the two spotted spider mite T. urticae

Influence of the secondary endosymbiont Serratia Symbiotica on the resistance to the parasitism in the aphid Acyrthosiphon pisum

peer reviewedAphids have an obligate association with the primary symbiont Buchnera aphidicola and is known to affect aphid fitness. Aphids commonly harbour other facultative bacterial endosymbionts and may benefit from their presence through increased resistance to parasitoids [1]. Present results suggest that the ability of hosts to defend against natural enemies depend not only on the presence of symbionts but also on the host genotype. Aphids represent a complex micro-environment for the parasitoid larvae and both the aphid physiology and endosymbiont influence their survival until mummification