Plant-Derived Insecticides Under Meta-Analyses: Status, Biases, and Knowledge Gaps

SIMPLE SUMMARY: Botanical insecticides have a burgeoning body of literature over the last decades, which potentially hides misconceptions and limitations in this research field. Here, we conducted a systematic review to recognize the current context of the field, including the temporal trends, the main botanical families, and the taxonomic groups explored in papers between 1945-2019. Next, we performed meta-analyses to identify any existing biases on such studies and realized existing knowledge gaps worthy of attention. The 74 years of our review tracked over 2500 scientific papers, which exhibit an exponential growth since the 1990s, always with prevalent interest on Meliaceae plant species, and a dozen additional families, albeit 190 botanical families were investigated. These articles primarily focused on pest insects with rather little attention devoted to non-target species. Besides, they concentrate on mortality assessments among arthropod species, overlooking sublethal assessments. Such outcomes highlight that sublethal effects remain poorly understood in both target and non-target organisms signaling a relevant gap to be filled, which will lead to novel insights allowing potential applications in pest management. ABSTRACT: Plant-derived or botanical insecticides are biopesticides experiencing substantial ongoing increase in interest. The 74 years of our literature survey tracked over 2500 papers on botanical insecticides published between 1945 and 2019 (Web of Science database). Such a survey allowed meta-analyses to recognize current status and biases of the studies providing important insights into the research topic. They include the recognition of the exponential growth of such studies since the 1990s, the prevalent interest on the Meliaceae plant species and a dozen additional families, although some 190 families have been investigated. The arthropods targeted by such studies were pest species (ca. 95%) with rather little attention devoted to non-target species (p < 0.001). This bias is followed by another one—mortality assessments are prevalent among target and non-target arthropod species when contrasted with sublethal assessments (p < 0.01). These omissions are pivotal, as they fail to recognize that sublethal effects may be as important or even more important than mortality, and that initial insecticide deposits quickly degrade over time leading to prevailing sublethal exposure. Furthermore, although the target of control is limited to few species, non-target species will be exposed and as such need to be factored into consideration. Thus, these biases in studies of botanical insecticides incur in knowledge gaps with potential consequences for the practical use of these compounds as pest management tools.