PEST MANAGEMENT Tarnished Plant Bug (Heteroptera: Miridae) Populations near Fields After Early Season Herbicide Treatment

A single herbicide (Trimec or Strike 3 ) application in early season (March or April) was made to marginal areas around Þelds in 23-km test sites of the Mississippi Delta in 1999, 2000, and 2001. The herbicide was used to kill broadleaf weeds in the marginal areas that served as hosts for tarnished plant bugs, Lygus lineolaris (Palisot de Beauvois). The herbicide treatment caused a signiÞcant reduction in wild host densities in the treated test sites in all 3 yr. Tarnished plant bug populations in treated test sites did not increase signiÞcantly in the treatedmarginal areas duringApril and May after treatment of the margins in the Þrst 2 wk of March in 2000 and 2001. The herbicide application was made in the Þrst 2 wk of April 1999, and plant bug populations increased in treated marginal areas in this year. The increase was thought to be caused by plant bugs moving to Italian ryegrass,LoliummultiflorumLamarck, a previously unreported plant bug host, whichwas not affected by the herbicide. Laboratory tests showed that plant bugswould oviposit in ßowering or nonßowering ryegrasswhencagedon ryegrass for a 6-dperiod.Newlyemergednymphsdeveloped into adults (56%) when reared on ßoral spikelets of ryegrass, but no adults were obtained when they were reared on ryegrass stems and leaves. Rearing on ßoral spikelets beginning with third-instar nymphs resulted in 92% adults, whereas third-instar nymphs reared on stems and leaves produced no adults. These results showed that ryegrass could serve as a reproductive host for plant bugs when it ßowered during late April and May. Application of the herbicide in March, when ryegrass was not in ßower, resulted in no signiÞcant increases in plant bug populations onwild hosts (mainly ryegrass) duringApril andMay in 2 yr of the Þeld study.