Thresholds for Management of Phorodon humuli (Hemiptera: Aphididae) on Hops

Abstract

The hop aphid, Phorodon humuli (Schrank), is one of the main hop, Humulus lupulus L. (Cannabaceae), pests in the world. The aim of this work was to determine (1) the yield loss function in hops based on the pest density of P. humuli, (2) and the economic injury level (EIL), economic threshold (ET), environmental economic injury level (EEIL) and environmental economic threshold (EET). Different densities of P. humili were applied to hop plants in the form of several aphid treatments over time. A negative correlation was found between yield and the number of aphids per square meter of canopy in accordance with the formula: y = [0.047 • x] / [1 + (0.047 • x) / 54.385], where: y = percentage of yield lost, and x = annual maximum number of aphids per square meter of canopy. Based on this formula, the economic injury level (EIL) was calculated as follows: [54.385 • C] / [2.556 • V• P0• K – 4.7 • C], where: C = total insecticide cost per hectare, V = hop price per kilogram, P0 = yield per hectare of a minimum pest level orchard, and K = reduction of injury due to treatment. The economic threshold (ET) obtained from the population dynamics of P. humuli was, on average, 0.7 EIL. The EEIL and the EET also were calculated: EEIL ≅ 1.66EIL and EET ≅ 1.66 ET ≅ 1.16 EIL. Other formulae relating the number of aphids per square meter with other simpler indices expressing these thresholds were calculated: aphids per leaf, percentage of infested leaves, infested leaves per frame, index of infestation, percentage of frames occupied, aphids per dm2 of leaf, aphids per 20 cm high volume and aphids per hop bine.