Response of predators to habitat manipulation in potato fields

Authors: Szendrei, Zsofia; Weber, Donald

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2009
Publication Date: 4/8/2009
Citation: Szendrei, Z., Weber, D. 2009. Response of predators to habitat manipulation in potato fields. Biological Control. 50(2):123-128. Available www.sciencedirect.com/science?.

Interpretive Summary: Pests are frequently preyed upon by multiple predators. To best manage the biological control provided by predators in the field, we need to know how these predators interact to suppress important pests. It is important not only to know which predators have the most impact alone, but also in combination with other predator species with which they occur in the field. Also, the effectiveness and interaction of different predators may differ under different field conditions such as presence or absence of tillage or mulch. This study was designed to assess the suppression of the key potato pest, Colorado potato beetle, by two predators which frequently occur together in potato fields. We used conventional (tilled) potato culture as well as a rye straw mulch, in multiple field cages. Each predator alone as well as two different predator combinations, were placed in the potato crop with pest eggs to determine the impact on the pest as it developed in the egg and larval stages. Our conclusions point to the importance of the predator carabid beetle Lebia grandis, which had a greater impact than the lady beetle Coleomegilla maculata which we also tested. In terms of pest suppression, combination of these two predators was additive (no negative or positive interactions between predators) and did not in this case respond to the tillage or mulch differently. This conclusion allows us to concentrate research on improving the potato crop environment for the conservation and encouragement of the more important predator, Lebia grandis.

Technical Abstract: Determining the impact of habitat complexity and predator species diversity on prey suppression is crucial in developing predictions for the impact of biological control programs. Biological control literature contains controversial evidence for the impact of increased predator species diversity and habitat complexity on prey suppression. We investigated the individual and combined effects of two predator species (Coleomegilla maculata and Lebia grandis) on the herbivore Leptinotarsa decemlineata in potato fields with and without rye mulch. In surveys of the endemic populations we detected that C. maculata is approximately 16 times more abundant than L. grandis and the two predator species responded in opposite manner to the habitat complexity treatment in potato fields: on average 35% of all C. maculata but 85% of all L. grandis collected over two field seasons were found in tilled vs. rye mulched plots. In field cages we investigated the effect of habitat complexity and predator identity on L. decemlineata suppression. Neither predator was influenced significantly by habitat complexity treatment. Lebia grandis was effective in suppressing the target prey relative to the control but C. maculata in the single species as well as in the two species assemblages was not consistently able to suppress prey relative to the control. This study found no support for positive multi-predator effects since the two predator species assemblages performed as predicted based on the results from individual predators. Practical implications of this study suggest focusing conservation biological control efforts – other than increased habitat complexity- on L. grandis to maximize its density in L. decemlineata infested potato fields.