Insect Pathogens As Biological Control Agents: Back to the Future
Total Page：16
File Type：pdf, Size：1020Kb
Accepted Manuscript Insect pathogens as biological control agents: back to the future L.A. Lacey, D. Grzywacz, D.I. Shapiro-Ilan, R. Frutos, M. Brownbridge, M.S. Goettel PII: S0022-2011(15)00134-2 DOI: http://dx.doi.org/10.1016/j.jip.2015.07.009 Reference: YJIPA 6706 To appear in: Journal of Invertebrate Pathology Received Date: 24 March 2015 Accepted Date: 17 July 2015 Please cite this article as: Lacey, L.A., Grzywacz, D., Shapiro-Ilan, D.I., Frutos, R., Brownbridge, M., Goettel, M.S., Insect pathogens as biological control agents: back to the future, Journal of Invertebrate Pathology (2015), doi: http://dx.doi.org/10.1016/j.jip.2015.07.009 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. JIP-15-82 1 Insect pathogens as biological control agents: back to the future 2 3 4 L. A. Lacey1, D. Grzywacz2 D. I. Shapiro-Ilan3, R. Frutos4, M. Brownbridge5, M. S. Goettel6 5 6 1 IP Consulting International, Yakima, WA, USA. [email protected] 7 2 Principal Scientist, Agriculture Health and Environment Department, Natural Resources Institute, 8 University of Greenwich, Chatham Maritime, Kent, ME4 4TB, UK [email protected] 9 3 U. S. Department of Agriculture, Agricultural Research Service, 21 Dunbar Rd., Byron, GA 10 31008, USA [email protected] 11 12 4 Professor, University of Montpellier 2, UMR 5236 Centre d'Etudes des agents Pathogènes et 13 Biotechnologies pour la Santé (CPBS), UM1-UM2-CNRS, 1919 Route de Mendes, Montpellier; 14 France [email protected] 15 16 5 Research Director, Vineland Research and Innovation Centre, 4890 Victoria Avenue North, 17 Box 4000, Vineland Station, Ontario L0R 2E0, Canada 18 [email protected] 19 6 Formerly with: Agriculture and Agri-Food Canada, Lethbridge Research Centre, Lethbridge, 20 Alberta, Canada. Current email address: [email protected] 21 1corresponding author 22 Keywords: microbial control; baculovirus; entomopathogenic bacteria; transgenes; 23 entomopathogenic fungi; entomopathogenic nematodes, Bacillus thuringiensis, Bt-crops 1 JIP-15-82 24 Abstract 25 26 The development and use of entomopathogens as classical, conservation and augmentative 27 biological control agents have included a number of successes and some setbacks in the past 15 28 years. In this forum paper we present current information on development, use and future 29 directions of insect-specific viruses, bacteria, fungi and nematodes as components of integrated 30 pest management strategies for control of arthropod pests of crops, forests, urban habitats, and 31 insects of medical and veterinary importance. 32 Insect pathogenic viruses are a fruitful source of MCAs, particularly for the control of 33 lepidopteran pests. Most research is focused on the baculoviruses, important pathogens of some 34 globally important pests for which control has become difficult due to either pesticide resistance 35 or pressure to reduce pesticide residues. Baculoviruses are accepted as safe, readily mass 36 produced, highly pathogenic and easily formulated and applied control agents. New baculovirus 37 products are appearing in many countries and gaining an increased market share. However, the 38 absence of a practical in vitro mass production system, generally higher production costs, limited 39 post application persistence, slow rate of kill and high host specificity currently contribute to 40 restricted use in pest control. Overcoming these limitations are key research areas for which 41 progress could open up use of insect viruses to much larger markets. 42 A small number of entomopathogenic bacteria have been commercially developed for control 43 of insect pests. These include several Bacillus thuringiensis sub-species, Lysinibacillus (Bacillus) 44 sphaericus, Paenibacillus spp. and Serratia entomophila. B. thuringiensis sub-species kurstaki is 45 the most widely used for control of pest insects of crops and forests, and B. thuringiensis sub- 46 species israelensis and L. sphaericus are the primary pathogens used for medically important 47 pests including dipteran vectors,. These pathogens combine the advantages of chemical 2 JIP-15-82 48 pesticides and microbial control agents (MCAs): they are fast acting, easy to produce at a 49 relatively low cost, easy to formulate, have a long shelf life and allow delivery using 50 conventional application equipment and systemics (i.e. in transgenic plants). Unlike broad 51 spectrum chemical pesticides, B. thuringiensis toxins are selective and negative environmental 52 impact is very limited. Of the several commercially produced MCAs, B. thuringiensis (Bt) has 53 more than 50% of market share. Extensive research, particularly on the molecular mode of action 54 of Bt toxins, has been conducted over the past two decades. The Bt genes used in insect-resistant 55 transgenic crops belong to the Cry and vegetative insecticidal protein families of toxins. Bt has 56 been highly efficacious in pest management of corn and cotton, drastically reducing the amount 57 of broad spectrum chemical insecticides used while being safe for consumers and non-target 58 organisms. Despite successes, the adoption of Bt crops has not been without controversy. 59 Although there is a lack of scientific evidence regarding their detrimental effects, this 60 controversy has created the widespread perception in some quarters that Bt crops are dangerous 61 for the environment. In addition to discovery of more efficacious isolates and toxins, an increase 62 in the use of Bt products and transgenes will rely on innovations in formulation, better delivery 63 systems and ultimately, wider public acceptance of transgenic plants expressing insect-specific 64 Bt toxins. 65 Fungi are ubiquitous natural entomopathogens that often cause epizootics in host insects and 66 possess many desirable traits that favor their development as MCAs. Presently, commercialized 67 microbial pesticides based on entomopathogenic fungi largely occupy niche markets. A variety 68 of molecular tools and technologies have recently allowed reclassification of numerous species 69 based on phylogeny, as well as matching anamorphs (asexual forms) and teleomorphs (sexual 70 forms) of several entomopathogenic taxa in the Phylum Ascomycota. Although these fungi have 3 JIP-15-82 71 been traditionally regarded exclusively as pathogens of arthropods, recent studies have 72 demonstrated that they occupy a great diversity of ecological niches. Entomopathogenic fungi 73 are now known to be plant endophytes, plant disease antagonists, rhizosphere colonizers, and 74 plant growth promoters. These newly understood attributes provide possibilities to use fungi in 75 multiple roles. In addition to arthropod pest control, some fungal species could simultaneously 76 suppress plant pathogens and plant parasitic nematodes as well as promote plant growth. A 77 greater understanding of fungal ecology is needed to define their roles in nature and evaluate 78 their limitations in biological control. More efficient mass production, formulation and delivery 79 systems must be devised to supply an ever increasing market. More testing under field conditions 80 is required to identify effects of biotic and abiotic factors on efficacy and persistence. Lastly, 81 greater attention must be paid to their use within integrated pest management programs; in 82 particular, strategies that incorporate fungi in combination with arthropod predators and 83 parasitoids need to be defined to ensure compatibility and maximize efficacy. 84 Entomopathogenic nematodes (EPNs) in the genera Steinernema and Heterorhabditis are 85 potent MCAs. Substantial progress in research and application of EPNs has been made in the 86 past decade. The number of target pests shown to be susceptible to EPNs has continued to 87 increase. Advancements in this regard primarily have been made in soil habitats where EPNs are 88 shielded from environmental extremes, but progress has also been made in use of nematodes in 89 above-ground habitats owing to the development of improved protective formulations. Progress 90 has also resulted from advancements in nematode production technology using both in vivo and 91 in vitro systems; novel application methods such as distribution of infected host cadavers; and 92 nematode strain improvement via enhancement and stabilization of beneficial traits. Innovative 93 research has also yielded insights into the fundamentals of EPN biology including major 4 JIP-15-82 94 advances in genomics, nematode-bacterial symbiont interactions, ecological relationships, and 95 foraging behavior. Additional research is needed to leverage these basic findings toward direct 96 improvements in microbial control. 97 98 1. Introduction 99 100 Since Lacey et al. (2001) addressed the possible future of microbial control of insects, the 101 development of microbial pesticides and implementation of microbial control has included a 102 number of successes and suffered some setbacks. Entomopathogens are utilized in all three 103 categories of biological control, classical, conservation and augmentative, as defined by Hoy 104 (2008a, 2008b) and McCrevy (2008).