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Biology of hop looper and its natural enemies

Biology of hop looper and its natural enemies

EB2037E
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Tessa Grasswitz, WSU Prosser Irrigated Agriculture Research and Extension Center, David James, WSU Prosser Irrigated Agriculture Research and Extension Center,
The hop looper is a native noctuid moth that was first reported as a pest of hops in the mid-1800s, but until recently has generally been regarded as a relatively minor and sporadic problem. However, it now seems to be developing into a more frequent and damaging pest, probably as a result of the gradual shift away from broad-spectrum organophosphate compounds for the routine control of aphids and mites to more selective products that provide no incidental control of loopers. Research conducted at WSU Prosser IAREC over the past three years has clarified many aspects of the basic biology and phenology of this pest, as well as identifying a variety of natural enemies and quantifying their impact. There is a need to extend this information to growers, as there are a number of misconceptions regarding this pest that need to be overcome if an integrated approach to it's management is to be achieved.
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Introduction

The hop looper, Hypena humuli, is a native noctuid moth widely distributed across the continental USA and Canada (Holland, 1905). The larvae usually feed only on hops, although they have occasionally been found on stinging nettle (Urtica sp.) (Grimble et al., 1992). The hop looper was first recorded as a pest of hops in the eastern US in the mid-1800s, but until recently has only been regarded as an occasional, or relatively minor, problem. However, hop looper is now beginning to re-emerge as a more frequent and damaging pest of Washington hops, probably as a result of the replacement of broad-spectrum organophosphate compounds for aphid and mite control by more selective products that provide little incidental control of loopers.

Biology and life history

Hop loopers overwinter in the adult stage. Both sexes of the adult have a distinctive, elongated snout that gave this species its original common name of “hop- vine snout moth.” The females have a distinctive W-shaped dark patch along the leading edge of each forewing (Fig. 1), while in males this mark is generally obscured by the darker and more uniform color of their wings (Fig. 2). As the males age, however, some of the surface scales on their wings may be lost, making them appear more like the females. The overall wingspan of both sexes is approximately 26 mm (1 inch).

The adults leave the hop yards in autumn (late September/October) to seek shelter elsewhere. They have been found overwintering in caves (Kikukawa, 1982; Godwin, 1987) and probably also use other protected sites such as cracks and crevices in tree trunks, fallen logs, fence posts, etc. The adults are thought to be capable of dispersing several miles to and from their overwintering sites, but the maximum extent of their migratory flight is not yet known. They return to the hop yards in early spring (late March/early April) and typically remain concealed within the hop foliage during the day, flying only at night or when disturbed.

Looper eggs may be found on hop foliage from mid- April onwards. The eggs are slightly flattened and are approximately circular when viewed from above, with an average diameter of 0.5 to 0.6 mm (about 1/5 inch) (Fig. 3). They are translucent and, when first deposited, have a faint greenish tinge which gradually disappears as the eggs mature and turn white. In general, just a single egg is found on each leaf, although it is not unusual to find two or three on the same leaf, and very occasionally as many as eleven have been found; in such cases,

Fig. 1. Adult female hop looper
Fig. 2. Adult male hop looper
however, the eggs are always laid singly, not in groups. The eggs are usually found on the underside of the leaf, either alongside a major vein (often at the point where the leaf blade joins the petiole) or on the leaf margin. Adult females can lay up to 600 eggs during their lifespan (three to four weeks for the summer generations), and it takes approximately three days for the eggs to hatch at a temperature of 26 °C (~79 °F). At this temperature, it takes the newly-emerged larvae fourteen to fifteen days to reach the pupal stage, and an additional nine days before the adults emerge. In the field some larvae will pupate on the plant (e.g., where two leaves overlap), while others pupate in the surface litter at the base of the plant or just beneath the soil surface.

 

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