Repellent usage against rodents is almost not provided anymore. Permission to use many rodent repellent substances under European Union (EU) plant protection regulations has not been renewed in recent years. Some approval for chemical substances have not been renewed due to their toxicological properties, and for some biorational approvals have also not been renewed due to lack of financial support together with other concerns. Some other rodent repellent substances possessing accurate properties in a secondary way have also been withdrawn. Thus, the use of almost ten active substances is now illegal. The lack of support and the resultant orphan use may be explained by the relatively small market and possible business together with the expectations of modern substance application requirements. As a result, the opportunity to consider new biorational substances as candidates is therefore open. Plant based food substances are preferred candidates for plant protection considering their favourable toxicological characteristics. Capsicum oleoresin, a mixture obtained from two spice species (Capsicum annuum and C. frutescens), is one of them with appropriate repellent properties. An application under EU Plant Protection Product regulation has recently been submitted and may become a new repellent for biological control agent against seed predators.
This study investigates the acaricidal, ovicidal, and repellent effects of the Tagetes patula Linn. (Asteraceae) leaf extract against both the adult female and egg stages of Tetranychus urticae Koch (Trombidiformes: Tetranychidae) under laboratory conditions. The Tagetes patula ethanolic leaf extract [TpEtOH70%] was screened for adulticide and ovicide bioassays in order to consider its acute toxicity. One sublethal concentration was used to assess egg-laying capacity (fecundity), repellent, and oviposition deterrent activities. The chemical characterization was conducted by gas chromatography-mass spectrometry (GC-MS) analysis to identify the TpEtOH70% bioactive components. Results showed that the LC50 value of TpEtOH70% leaf extract predicted by Probit analysis against T. urticae adult females at 24 h was 0.99%. The TpEtOH70% leaf extract showed a significant toxic effect as the highest mean mortality rates (± SE) of the treated adult females was 88.9 ± 3.7%. However, the TpEtOH70% leaf extract was insignificant in affecting the egg-laying capacity of the adult females treated with a sublethal dose of 0.5% even after 72 h. The TpEtOH70% leaf extract was classified repellent since the repellent index (RI) value was lower than 1 – SD. In addition, it had a high oviposition deterring effect based on a 100% reduction of the total number of eggs. The TpEtOH70% leaf extract had a significant ovicidal effect on T. urticae eggs, with 56.04% reduction in hatching. Five bioactive compounds from various classes of phytochemicals were identified in the TpEtOH70% leaf extract and the major compound was phytol (62.72%). This pioneering investigation reveals the adulticidal, ovicidal, and repellent activities of the TpEtOH70% leaf extract against T. urticae. A combination of multiple modes of action of different plant components may act alone or in synergism to delay the development of mite resistance.