Pseudaletia unipunctra, the true armyworm, is endemic on all continents, being an indiscriminate pest of field crops and horticultural species. The moth is known to be migratory and in Canada (and some other temperate regions) the species enters afresh each spring from the south. Because of this behaviour, the pest may appear suddenly in large numbers. The moths lay eggs in May/June which hatch into the damaging larval (armyworm) stage during June/July. There are two generations per year in most places. Each generation consists of an egg stage, which hatches into ti larvae, which when fully grown, enter the pupal stage, during which metamorphosis occurs giving rise to the adult moth. These then mate and lay eggs so that the cycle begins over again. Thus, if moths are present in a locale, eggs and armyworms can be expected to appear there subsequently.
The presence of the moth in a locality is usually assessed by light trapping, wherein a bright light is used to lure the moths to a trap at night, during the periods when the moth is in flight. This technique has long been known and remains in wide use today. However, light lures indiscriminately bring many other moths, along with beetles and other insects, to the trap also; sorting is thus necessary. In practice, comparative light trapping is expensive and time-consuming, and expertise is required. A more convenient method of sampling local populations would use a simpler, cheap trap and a specific lure.
The compound (Z)-11-hexadecen-1-yl acetate (Z11-16:Ac) has been found in abdominal tip extracts and in effluvium from female moths of the common armyworm and has been confirmed as the primary sex pheromone component for P. unipuncta (see Hill and Roelofs "Environmental Entomology", Vol. 9, No. 4, p. 408-411, August 1980). McDonough et al, J. of Chem. Ecology, Vol. 6, No. 3, p. 565-572, 1980, also identified Z11-16:Ac, a hexadecen-1-o1 (believed to be (Z)-11 isomer), and possible (Z)-9-hexadecen-1-yl acetate, in extracts of the female armyworm moths. In field tests, no combination of compounds was found to be more attractive than Z11-16:Ac alone. Farine et al confirmed the presence of Z11-16:OH in the natural extract and found (in addition to Z11-16:Ac) that hexadecanyl acetate and Z9-16:Ac were also present (see C.R. Acad. Sc. Paris, t. 292, Series III, p. 101-104, Jan. 5, 1981).
In early tests, we had found that Z11-16:Ac with 0.1-0.5% (Z)-11-hexadecenol produced a reasonably effective and specific lure for the male armyworm moths. The attraction was increased on adding trace amounts (e.g. 0.01%) of (Z)-9-tetradecen-1-yl acetate (Z9-14:Ac). (See W. Steck et al, "Environmental Entomology", Vol. 9, No. 5, p. 583-585, October 1980). In tests on Polia atlantica we had tried the ternary mixture Z11-16:Ac+Z11-16:OH+Z11-16:Ald in the weight ratios 200:1:1 and found it ineffective for this species (see Table 2 in this latter reference). Some or all of these latter three compounds are known to be present in attractants for other species but the ratios are vastly different and the previously described mixtures are substantially nonattractive to armyworm moths.