Integrating adverse effect analysis into environmental risk assessment for exotic generalist arthropod biological control agents: a three-tiered framework

Environmental risk assessments (ERAs) are required before utilizing exotic arthropods for biological control (BC). Present ERAs focus on exposure analysis (host/prey range) and have resulted in approval of many specialist exotic biological control agents (BCA). In comparison to specialists, generalist arthropod BCAs (GABCAs) have been considered inherently risky and less used in classical biological control. To safely consider exotic GABCAs, an ERA must include methods for the analysis of potential effects. A panel of 47 experts from 14 countries discussed, in six online forums over 12 months, scientific criteria for an ERA for exotic GABCAs. Using four case studies, a three-tiered ERA comprising Scoping, Screening and Definitive Assessments was developed. The ERA is primarily based on expert consultation, with decision processes in each tier that lead to the approval of the petition or the subsequent tier. In the Scoping Assessment, likelihood of establishment (for augmentative BC), and potential effect(s) are qualitatively assessed. If risks are identified, the Screening Assessment is conducted, in which 19 categories of effects (adverse and beneficial) are quantified. If a risk exceeds the proposed risk threshold in any of these categories, the analysis moves to the Definitive Assessment to identify potential non-target species in the respective category(ies). When at least one potential non-target species is at significant risk, long-term and indirect ecosystem risks must be quantified with actual data or the petition for release can be dismissed or withdrawn. The proposed ERA should contribute to the development of safe pathways for the use of low risk GABCAs

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The cotton aphid, Aphis gossypii, is a major pest in eggplant crops grown in greenhouses throughout Japan. This species easily becomes resistant against insecticides. A promising way to control these aphids biologically is with banker plants. Then, the alternative prey, Rhopalosiphum padi, on these plants should guarantee a permanent production of the general predator, larvae of the gall midge Aphidoletes aphidomyza which prefer to eat the pest insect. When the pest in the crop is scarce the banker plant should serve as a refuge for the general predator. With a differential equation model we show under which conditions biological control in this specific system can be called successful. We discuss whether the mathematical conclusions are biologically feasible

Evaluation of pest control efficiencies for different banker plant systems with a simple predator–prey model

The banker plant system has been introduced for the biological control of various pest species in Japanese greenhouses. With the banker plant system, non-crop plants infested with a host insect (a non-commercial crop pest) are placed in the greenhouse to provide alternative resources for the parasitoids or predators. We want to evaluate the effectiveness for controlling pests on the crop in a quantitative way by immigrating predators from the banker plant. Therefore, we developed a simple model for the interaction of the pest and predator in the crop and included the banker plant only as a source for predators. For three different pest-predator systems we parameterised the model and used these models to predict under what conditions biological control in a banker plant system is successful. We defined successful as keeping the pest below the economic injury level of the crop estimated from damage analysis. Because the crop is mostly grown during a period that lasts less than a year our analysis should not only focus on the equilibrium dynamics. In contrast, it should also focus on the transient dynamics. Our main analytical result, from the equilibrium analysis, is that for successful control the maximum lifetime consumption of immigrating predators should exceed the daily prey growth at half the value of the maximum consumption rate. For practical purpose this translates into the fact that the immigration of predators at a low initial pest density is crucial for successful control.</p

Effects of aphid honeydew sugars on the survival and fecundity of the aphidophagous gall midge Aphidoletes aphidimyza

Predatory gall midge Aphidoletes aphidimyza, which is used for augmentative biological control of aphids in greenhouses, take aphid honeydew as an energy source to survive. Currently Rhopalosiphum padi on barley plants and Melanaphis sacchari on sorghum plants are used as the banker plant systems for A. aphidimyza to control A. gossypii on eggplants in Japan. We analyzed the sugar components of three species aphid honeydew by HPLC. The major components of honeydew were sucrose, fructose and melezitose for A. gossypii, glucose and fructose for R. padi and glucose, fructose and melezitose for M sacchari. Two minor components for these three aphid species were maltose and trehalose. We investigated the influence of sugars including three aphid artificial honeydew, six sugar components of three species aphid honeydew and water on the longevity of unmated females and males of A. aphidimyza. Both females and males attained the longest lifespan on sucrose and artificial honeydew of A. gossypii. Mean longevities of both females and males were shortest when they were provided with only water. We conducted another experiment where a mated female was released in a cage with an eggplant seedling infested with A. gossypii and was fed with sucrose or only water. Number of eggs laid and survival of the female was examined every day. Females fed with sucrose lived significantly longer and laid more eggs in their lifetime than those with only water