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      Invader Competition with Local Competitors: Displacement or Coexistence among the Invasive Khapra Beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae), and Two Other Major Stored-Grain Beetles?


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          Local potential competitor species are important determinants of the invasibility of an environment even when widely recognized invasive species are concerned since it may compromise its establishment. Thus, the outcome of the direct competition among the invasive khapra beetle, Trogoderma granarium, and the cosmopolitan species lesser grain borer, Rhyzopertha dominica and rice weevil, Sitophilus oryzae, and thus the likelihood of establishment of T. granarium under their co-occurrence, was here explored in paddy rice and wheat, at temperatures between 25 and 35 °C and through 200 days of storage. Insect infestations were higher in wheat rather than in paddy rice. Trogoderma granarium was unable to displace any of the competing species under two and three-species competition experiments retaining lower adult population than both local competitors at the lowest temperature level. Rhyzopertha dominica prevailed in paddy rice, while S. oryzae prevailed in wheat. Paradoxically, T. granarium adults retained low population growth but contributed more for the total frass production and grain loss, much more than that recorded for R. dominica. Nonetheless, T. granarium larvae exhibited high population numbers 130 days after the introduction of the parental individuals. At higher temperature levels (30 and 35 °C) the numbers of T. granarium larvae were extremely high even after 65 days, while the numbers of the other two species rapidly declined. Interestingly, the simultaneous presence of R. dominica and S. oryzae was beneficial for the population growth of T. granarium. Consequently, T. granarium has the ability to outperform other primary stored-product insects at high temperatures, while its presence at low temperatures remains for long periods apparently unaffected by other co-occurring species. Hence, T. granarium, in wheat, is able to outcompete other major species of stored-product insects at elevated temperatures, while at 25 °C this species can maintain low numbers of individuals for long periods, which can rapidly produce population outbursts when the prevailing conditions are suitable for its development.

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          Population-level effects of pesticides and other toxicants on arthropods.

          New developments in ecotoxicology are changing the way pesticides and other toxicants are evaluated. An emphasis on life histories and population fitness through the use of demography, other measures of population growth rate, field studies, and modeling are being exploited to derive better estimates of pesticide impacts on both target and nontarget species than traditional lethal dose estimates. We review the state of the art in demographic toxicology, an approach to the evaluation of toxicity that uses life history parameters and other measures of population growth rate. A review of the literature revealed that 75 studies on the use of demography and similar measures of population growth rate in toxicology have been published since 1962. Of these 75 studies, the majority involved arthropods. Recent evaluations have indicated that ecotoxicological analysis based on population growth rate results in more accurate assessments of the impacts of pesticides and other toxicants because measures of population growth rate combine lethal and sublethal effects, which lethal dose/concentration estimates (LD/LC50) cannot do. We contend that to advance our knowledge of toxicant impacts on arthropods, the population growth rate approach should be widely adopted.
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            Eradication of Invading Insect Populations: From Concepts to Applications.

            Eradication is the deliberate elimination of a species from an area. Given that international quarantine measures can never be 100% effective, surveillance for newly arrived populations of nonnative species coupled with their eradication represents an important strategy for excluding potentially damaging insect species. Historically, eradication efforts have not always been successful and have sometimes been met with public opposition. But new developments in our understanding of the dynamics of low-density populations, the availability of highly effective treatment tactics, and bioeconomic analyses of eradication strategies offer new opportunities for developing more effective surveillance and eradication programs. A key component that connects these new developments is the harnessing of Allee effects, which naturally promote localized species extinction. Here we review these developments and suggest how research might enhance eradication strategies.
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              Two complementary paradigms for analysing population dynamics.

              To understand why population growth rate is sometimes positive and sometimes negative, ecologists have adopted two main approaches. The most common approach is through the density paradigm by plotting population growth rate against population density. The second approach is through the mechanistic paradigm by plotting population growth rate against the relevant ecological processes affecting the population. The density paradigm is applied a posteriori, works sometimes but not always and is remarkably useless in solving management problems or in providing an understanding of why populations change in size. The mechanistic paradigm investigates the factors that supposedly drive density changes and is identical to Caughley's declining population paradigm of conservation biology. The assumption that we can uncover invariant relationships between population growth rate and some other variables is an article of faith. Numerous commercial fishery applications have failed to find the invariant relationships between stock and recruitment that are predicted by the density paradigm. Environmental variation is the rule, and non-equilibrial dynamics should force us to look for the mechanisms of population change. If multiple factors determine changes in population density, there can be no predictability in either of these paradigms and we will become environmental historians rather than scientists with useful generalizations for the population problems of this century. Defining our questions clearly and adopting an experimental approach with crisp alternative hypotheses and adequate controls will be essential to building useful generalizations for solving the practical problems of population management in fisheries, wildlife and conservation.

                Author and article information

                Front Plant Sci
                Front Plant Sci
                Front. Plant Sci.
                Frontiers in Plant Science
                Frontiers Media S.A.
                07 November 2017
                : 8
                : 1837
                [1] 1Laboratory of Agricultural Zoology and Entomology, Department of Crop Science, Agricultural University of Athens , Athens, Greece
                [2] 2Laboratory of Entomology and Agricultural Zoology, Department of Agriculture, Crop Production and Rural Environment, University of Thessaly , Volos, Greece
                [3] 3Departamento de Entomologia, Universidade Federal de Viçosa , Viçosa, Brazil
                [4] 4Laboratory of Organic Chemistry, Department of Chemistry, University of Ioannina , Ioannina, Greece
                Author notes

                Edited by: Thomas Miedaner, University of Hohenheim, Germany

                Reviewed by: Tom Phillips, Kansas State University, United States; Waqas Wakil, University of Agriculture Faisalabad, Pakistan; Enric Frago, Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD), France

                *Correspondence: Nickolas G. Kavallieratos, nick_kaval@ 123456hotmail.com

                This article was submitted to Plant Breeding, a section of the journal Frontiers in Plant Science

                Copyright © 2017 Kavallieratos, Athanassiou, Guedes, Drempela and Boukouvala.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

                : 06 June 2017
                : 10 October 2017
                Page count
                Figures: 10, Tables: 1, Equations: 0, References: 69, Pages: 17, Words: 0
                Funded by: Ministério da Educação 10.13039/501100006366
                Plant Science
                Original Research

                Plant science & Botany
                insects’ competition,species displacement,competitive exclusion,species co-existence,storedproducts,quarantine species


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