EXPLORING SYNERGISMS OF BIOCONTROL AND PLANT RESISTANCE IN LEVEL III IPM Opening lecture – 15o SICONBIOL Marcos Kogan (Oregon State University, EUA) Host plant resistance and biocontrol are the two fundamental pillars of IPM. Of all the control tactics in the IPM arsenal, they are the ones with the most robust ecological foundations, and, in a few crop situations, one or the other alone or in combination have been responsible for keeping arthropod pest populations below an economic injury level. In 1980, the concept of tri-trophic interactions, i.e., the interactions between the host plant, the herbivore and its natural enemies, was introduced in the insect ecology literature. Since then much research has been conducted on the role of the host plant on the effectiveness of the natural enemies in regulating the herbivore pest population. Secondary compounds and physical traits that coevolved with the herbivores attacking the plant possessing those traits, have been shown to have positive or negative impacts on the complement of natural enemies of the herbivores. Recent research explored the possibility of incorporating this knowledge by removing from crop plants the negative factors or incorporating or augmenting the positive ones. Traditional plant breeding has resulted, in many crops, in the inadvertent loss of defensive traits. Some of these traits impose a metabolic coast to the plant that breeders prefer to invest in the increase of yields or the taste or cosmetic appearance of the crop product. Examples of loss of defenses in improved varieties are now available for several crops. The concept recently advanced in various parts of the world is to explore through traditional breeding procedures or using genetically engineering options to target specifically traits that favor the natural enemies in the tri-trophic system. The use of these traits is not necessarily limited to the simple combination of plant resistance and biocontrol, but also for use in conservation biocontrol, push-and-pull systems, trap crops, companion crops, and others. This brings us to the potential of these techniques to advance IPM to level III integration. Level III integration refers to pest management conceived at the ecosystem scale. To our knowledge, at present, few, if any IPM programs have been implemented at this level. This is, however, a goal that pest managers should aspire. For the purpose of this discussion the target ecosystem encompasses all crop fields and the surrounding natural vegetation, within a region defined by common physiographic and climatic conditions. Operating at such scale usually exceeds the control or decision-making by individual farmers and requires area-wide cooperation by farmers, plant-protection extension and research specialists. This level of cooperation can only be achieved by careful planning, a high level of communication, and government financial support. RESUMOS DOS PALESTRANTES ESTRANGEIROS Palestrante: Alejandra Bravo (UNAM, México) E-mail: [email protected] Titulo: Mode of action of Bacillus thuringiensis toxins Bacillus thuringiensis (Bt) produce different insecticidal toxins named Cry toxins that are used extensively in the control of different insect pest and in the control of insect vectors of human diseases. In this presentation, we will summarize recent findings on the mechanism of action of Cry toxins. Cry proteins are produced as protoxins of 130 kDa that after activation with proteases resulted in a toxin size of 60 kDa. The activated Cry toxins are modular proteins comprised of three domains connected by single linkers. Cry toxins interact with multiple receptor molecules leading to the formation of membrane pores in midgut cells of susceptible insects. Cry1Ab protoxin or activated-toxin are able to bind cadherin with similar affinities, the interaction with cadherin induces the oligomerization of the toxin, toxin oligomers bind with high affinity to specific receptor such as Aminopeptidase N (APN) and Alkaline phosphatase (ALP) that help during insertion of the oligomer into the membrane. We propose a dual mechanism of action since we observed that two different pre-pores are produced depending if protoxin or activated toxin interacts with cadherin. These pre-pores differ in their apparent-size, sensitivity to temperature, capability to insert into synthetic membranes and their pore characteristics. The fact that different lepidopteran insect have developed resistance to activated Cry toxin but still are susceptible to Cry protoxin supports the dual mode of action where both pre-pores are involved in toxicity.An alternative model of Cry toxin action was proposed based in results obtained in an insect cell line Tni-H5 transfected with the cadherin gene from Manduca sexta, this alternative model proposes that interaction with cadherin activates a signal transduction cascade that activates a protein G. The protein G activates an Adenilate Cyclase that increases the concentration of cAMP. The cAMP activates a PKA protein that is responsible of killing the insect cell. We analyzed the mechanism of action of Cry1Ab and Cry1Ac in another insect cell line CF-1 that is naturally susceptible to these toxins. We show that CF-1 cells are kill by Cry toxins due to the pore formation activity of the toxin and that PKA, and Adenilate Cyclase did not participate in killing these cells. These data indicate that the proposed alternative mode of action of Cry toxin is not functional in all cell lines. Palestrante: Bala Devisetty (Valent BioSciences Corporation, EUA) E-mail: [email protected] Titulo: Biological insecticide formulations Biological insecticide products derived from Bacillus thuringiensis subsp. kurstaki (B.t.k) and Bacillus thuringiensis subsp. aizawai (B.t.a) are the most widely used microbial products in agriculture and are used alone, in integrated pest management (IPM) programs, in rotation with conventional pesticides for effective larval control of some pests from the lepidopterous order of insects. Bacillus thuringiensis subsp. tenebrionis (Bt.te) is another microbe developed for control of some coleopteran pests such as Colorado potato beetles (Leptinotarsa decemlineata). Similarly, Bacillus thuringiensis subsp. israelensis (B.t.i) and Bacillus sphaericus (B.s) are two other microbial derived products of great importance in Public Health programs for control of various diseases caused by mosquito and black fly vectors. Commercial production of Bacillus spp. generally involves submerged fermentation. Several production parameters including media type, mineral nutrients and their concentrations, antifoams, growth conditions, recovery and processing methods can all affect physical and biological properties of the bacterium as well as products formulated from it. Similarly, formulation type, composition and manufacturing processes may have substantial influence on physical properties, stability, biological efficacy, and environmental persistence of the biological insecticide. Additionally, application methods, insect type and larval growth stage, environmental conditions, and tank-mixes with adjuvants, pesticide formulations and plant nutrient mixes can all affect the formulation’s biological stability and efficacy. Progress will be reviewed on the development of stable, efficacious, high potency and cost- effective novel biological insecticide formulations, specifically those based on Bacillus thuringiensis subsp. kurstaki, strain ABTS-351, Bacillus thuringiensis subsp. aizawai, strain ABTS-1857, Bacillus thuringiensis subsp. israelensis, strain AM 65-52 and Bacillus sphaericus, strain ABTS-1743 to suit a crop or crop stage, insect pest, habitat, application equipment and storage environment. Recent developments and research trends related to novel formulations toward enhanced spectrum of biological activity, persistence and resistance management will be emphasized. Palestrante: Benjamin de Havilland Raymond (Exeter University, UK) E-mail: [email protected] Titulo: The use of self-limiting insect release to overcome Bacillus thuringiensis resistance Genetically modified insects are of increasing interest as tools for managing pests. Supressible dominant lethal constructs, such as the ‘RIDL’ self limiting technology developed by Oxitec, can be thought of as genetic replacements of sterile insect release. In both SIT and RIDL large numbers of released males supress the reproductive potential of females. However, if RIDL lethality is restricted to females it is possible both to suppress populations and to introgress substantial genetic material into pests via the male line. Earlier experiments and theory indicated that female specific RIDL can supress the evolution of resistance to Bacillus thuringiensis toxins. Using a range of selection experiments with Cry1Ac resistant diamondback moth, Plutella xylostella, we explored the conditions that would facilitate resistance management using both RIDL and a high dose / refuge strategy. We found that, compared to theoretical predictions, a relatively high release ratio and a low initial frequency of resistance alleles made resistance management with RIDL feasible. Discrepancies between theory and experiments could be explained by the lower than expected competitivenes of RIDL males and by population dynamic effects. Further work has explored how to optimise the culture and release of genetically modified insects for resistance management. We have explored different strategies for releasing insect in structured populations