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United States Department of Agriculture

Agricultural Research Service

Title: Areawide Management of the Cotton Boll Weevil: Use of a Spatiotemporal Model in Augmentative Biological Control

Authors
item Legaspi, Benjamin - TX AGRI EXPER STATION
item Allen, J - UNIV OF FL, GAINSVILLE
item Brewster, C - UNIV OF FL, GAINSVILLE
item Morales Ramos, Juan
item King, Edgar

Submitted to: Ecological Modelling
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 8, 1998
Publication Date: N/A

Interpretive Summary: When biological control of an insect pest is attempted over a large area, key questions are: how many natural enemies do you release, when should you release them, and how do you position your release points so you can expect highest numbers of pests killed with the fewest numbers of natural enemies released? Computer models are useful tools in answering these questions because they allow scientists to simulate many different scenarios that would otherwise be too expensive or time consuming to do in reality. These models have been helpful in answering the first two questions, but the last question is only now being addressed by a new type of model that allows scientists to investigate the effects of space. We are developing such a model using as an example the boll weevil and one of its parasites. We used the model to explore different biological control strategies by comparing different release methods, e.g. releasing parasites for one site or many sites, or even from aircraft. We also tested possible effects of wind and variations in pest numbers and temperature. Our findings show the parasites are more effective at controlling the weevil when they are released over many sites or from the air, even though identical numbers of parasites are used. We are currently collecting more data to improve the reliability and accuracy of this model. With further development, the model should be useful in designing strategies for applied biological control of the boll weevil, or other pests, as part of a large scale integrated pest management program.

Technical Abstract: Recent advances in computer technology have facilitated the development of spatiotemporal models for simulation of ecological systems. The explicit modeling of space allows scientists to investigate the effects of spatial arrangements and heterogeneities, as well as temporal changes, in model systems. We describe an example of a host-parasitoid spatiotemporal model consisting of integrodifference equations, which model both biological processes and population dispersal. Our model ecosystem consists of the host, boll weevil, (Anthonomus grandis Boheman) (Coleoptera: Curculionidae) and its exotic parasitoid, Catolaccus grandis (Burks) (Hymenoptera: Pteromalidae). We use the model to explore different strategies in the augmentative biological control of the host by simulating different release methods (single or multiple sites, aerial release), and the effects of wind and heterogeneities in host density on efficacy of the parasitoid. Our preliminary simulations indicate greater host suppression when the parasitoid is released over multiple sites, or aerially, despite identical release rates. The methods used to simulate wind effects resulted in plausible; dispersal and parasitization patterns, but the inclusion of heterogeneities in host densities resulted in perhaps nonintuitive parasitization patterns, likely due to boundary effects. Data are being collected currently for calibration and validation of this model. With further development, this spatial model should be useful in designing optimal strategies for the augmentative release of C. grandis against the boll weevil as part of an areawide integrated pest management program.

Last Modified: 4/19/2014
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