Botanical insecticide research: many publications, limited useful data Murray B. Isman 1 and Michael L. Grieneisen 2, 3 1 Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC V6T1Z4, Canada 2 AGIS Lab, Department of Land, Air and Water Resources, University of California, Davis, CA 95616, USA 3 Wenzhou Medical University, Wenzhou, Zhejiang 325035, China Our analysis of >20 000 papers on botanical insecticides from 1980 to 2012, indicates major growth in the number of papers published annually (61 in 1980 to 1207 in 2012), and their proportion among all papers on insecticides (1.43% in 1980 to 21.38% in 2012). However, only one- third of 197 random articles among the 1086 papers on botanical insecticides published in 2011 included any chemical data or characterization; and only a quarter of them included positive controls. Therefore, a substan- tial portion of recently published studies has design flaws that limit reproducibility and comparisons with other and/or future studies. In our opinion, much of the scientific literature on this subject is of limited use in the progress toward commercialization or advancement of knowledge, given the resources expended. The allure of plant natural products Consumers in many regions of the world continue to be drawn to products based on plant (or other) natural products as alternatives to mainstream medicines, cosmetics, and cleaning products. The allure of natural products is based on the often invalid assumption that ‘natural is safe – synthetic is hazardous’ (e.g., [1,2]), likewise with products intended to kill or otherwise mitigate insect pests (i.e., insecticides). The negative public perception of conventional (synthetic) insec- ticides is well founded, given the demonstrated negative environmental and health impacts of many synthetic insec- ticides. However, that perception, deeply ingrained in the public mindset particularly in wealthy countries, is largely based on insecticides used through the latter half of the 20th century. In fact, many of these insecticides were eliminated from the agrochemical arsenal as early as 20 years ago, and replaced by synthetic insecticides with reduced health and environmental impacts. This negative perception, together with a greater scien- tific understanding of potential negative impacts of pesti- cides on human health and the environment, is driving their increasingly stringent regulation in highly developed countries. These considerations provide an impetus for the discovery and development of more environmentally be- nign and less hazardous insecticides. Among these are the botanicals, either crude extracts or naturally occurring chemicals derived from plants. Plants have evolved com- plex, and often effective, chemical arsenals to limit the damage inflicted on them by herbivorous insects [3]; and the use of botanicals is one of many strategies to protect plants from microbial pathogens [4] and nematodes [5]. Many plant defensive metabolites have clearly demon- strated mechanisms of insecticidal [6] or repellent [7,8] actions. Examination of the scientific literature in the field of botanical insecticides covering the past 30 years demon- strates a strong and growing academic interest in this area. However, is this surge in research activity on botanicals driving progress toward the discovery and/or commerciali- zation of effective plant-based insect control methods? Unfortunately, for a large proportion of recently published studies, we think not. Here, we document the growth of botanical insecticide research, the recent surge in research on essential oils as insecticides, and the widespread occur- rence of two methodological flaws that undermine the reproducibility and interpretation of the results from this fast-growing body of literature. The renaissance of botanical insecticides research Botanical insecticides, such as nicotine and pyrethrum, once dominated crop protection and domestic pest control, before the discovery of the insecticidal properties of DDT and methyl parathion during the late 1930s [9]. With the discovery of additional inexpensive and highly efficacious synthetic insecticides (organochlorines, organopho- sphates, and carbamates), botanicals were quickly trivial- ized in the pest control marketplace from the 1970s onward [10], and today occupy a small market share (e.g., <0.05% of all pesticides used in California in 2011), even within the category of biopesticides, which is dominated by products derived from the bacterium Bacillus thuringiensis. Our analysis indicates that only 1.43% of papers pub- lished on insecticides in 1980 dealt with botanical insecti- cides. However, a scientific ‘renaissance’ in interest in botanical insecticides was spurred by the Western ‘discov- ery’ of the profound anti-insect bioactivity of the triterpe- noid azadirachtin, isolated from the seeds of the Indian neem tree (Azadirachta indica, Meliaceae) during the 1960s [9]. Neem and neem-based insecticides became the subject of numerous studies, and several international conferences focusing on neem were held during the 1980s Opinion 1360-1385/$ – see front matter ß 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.tplants.2013.11.005 Corresponding author: Isman, M.B. (murray.isman@ubc.ca). Keywords: botanical insecticides; essential oils; natural products; chemical composi- tion; positive controls. TRPLSC-1119; No. of Pages 6 Trends in Plant Science xx (2013) 1–6 1