from both cultures into the field and offered them to N. clavipes. The spiders consistently freed the moths raised on CS diet [whose PA content matched that of field-raised Utetheisa (10)] but killed and consumed the PA-free controls (Figure 2B). We also tested directly for the deterrency of PA. We added crystalline monocrotaline to edible items (mealworms) ordinarily consumed by N. clavipes and found that by doing so we could render such items relatively unacceptable to the spiders (6).
Adult Utetheisa tend to be rejected also by birds (blue jays, Cyanocitta cristata; scrub jays, Aphelocoma coerulescens; T.E., unpublished observations), as might be expected, given their aposematism, but there is no definitive evidence that the unacceptability is due specifically to the PAs.
Tests with larval Utetheisa showed these to be rejected by wolf spiders, but only if the larvae had fed on Crotalaria or CS diet. Larvae raised on PB diet proved consistently palatable to the spiders (11).
Utetheisa, like many other insects, court at dusk (Figure 1D). The female initiates the behavior. Positioned on vegetation (often on branches of Crotalaria itself), she emits a sex attractant that drifts downwind and lures males (12). Caged virgin females, placed outdoors, attract males (Figure 3A). The glands that produce the pheromone are a pair of long, coiled tubes, opening close together near the abdominal tip (Figure 3C). Extraction of the glands led to the characterization of a long-chain polyene (3), which proved electrophysiologically active on male antennae
We found female Utetheisa to emit their attractant in pulses (1.5 ± 0.2 pulses per s) (12) (Figure 3D), as some other moths have since also been shown to do (14, 15). Pulsation frequencies are similar in the various