Damage from the larkspur mirid deters cattle grazing of larkspur

Abstract

The larkspur mirid (Hopplomachus affiguratus) is host specific to tall larkspur (Delphinium barbeyi Huth). These insects suck cell solubles from leaves and reproductive racemes, causing flowers to abort and leaves to desiccate. Cattle generally prefer lark spur flowering heads, pods, and leaves, and are frequently poisoned. The objective of this experiment was to determine if cattle would avoid eating mirid-damaged larkspur. A 2-choice cafeteria feeding trial was conducted to determine preference for mirid-damaged and undamaged larkspur. Four cows were offered a choice of the 2 types of larkspur in 10 min. feeding trials in the morning and evening for 5 days. Cows preferred the undamaged larkspur plants (0.8 kg +/- 0.08, SE) over mirid-damaged plants (0.1 kg +/- 0.03, SE). The cows were then turned out into a larkspur-infested pasture and consumption of mirid-damaged and undamaged larkspur was quantified by bite count. The cows did not select any mirid-damaged larkspur. Consumption of undamaged larkspur peaked at 17% of bites on the second day of the grazing trial, then declined as mirid damage on the plants increased. If the density of mirids on larkspur is sufficiently high to damage most of the leaves and flowering racemes, grazing by cattle may be deterred, and subsequent poisoning avoided.