Alfalfa management affects infestations of Lygus rugulipennis (Heteroptera: Miridae) on strawberries in northwestern Italy

Lygus rugulipennis (Heteroptera: Miridae) is a highly polyphagous plant bug that causes severe damage on everbearing strawberries in NW Italy. In this area strawberry fields are frequently surrounded by alfalfa and other forage crops on which plant bugs usually live and reproduce until mowing or harvest. A 3-year research study was conducted to test the attractiveness of some herbs, including alfalfa, for ovipositing L. rugulipennis females, and to evaluate if appropriate management of neighbouring forage crops could affect bug infestation levels and damage to strawberries. In 2005, the attractiveness to ovipositing females of four plant species (strawberry, alfalfa, red clover and chamomile), each of which is abundant in NW Italy, was evaluated in laboratory trials. In 2006 and 2007, the seasonal abundance of plant bugs on strawberries and alfalfa was monitored in an experimental strawberry field with a strip of alfalfa along two sides. During field surveys, the influence of alfalfa management, including insecticide treatments in 2007, on plant bug numbers was assessed. In the laboratory, females of L. rugulipennis preferred, in decreasing order, chamomile, alfalfa, red clover and strawberry for oviposition. However, in the field, the majority of nymphs were collected on strawberries over most of the growing season, showing that L. rugulipennis is able to reproduce and develop on this plant. During field surveys, more species of plant bugs, and more individuals, were observed on alfalfa, which although attractive for mirid bugs did not prevent their migration to strawberries during periods of high population density. At such times, an insecticide treatment on alfalfa kept plant bug infestations on strawberries under the economic threshold.