Lepidoptera larvae are capable of orienting towards or away from plants by using odors as cues but whether this attraction is innate or secondarily acquired remains unknown. We tested the hypothesis that European corn borer (ECB) neonate larvae express an innate attraction towards odors released from maize, and avoidance towards odors from spinach. Neonate larvae were placed on a locomotion compensator within a constant stream of humidified air that was loaded intermittently with airborne odors drawn from potted plants. The odor stream was delivered continuously or pulsed (1 to 10 sec pulses) at 40 ml/min. ECB larvae oriented toward maize odors pulsed at 2 to 6 sec but walked away from maize odors delivered at lower frequencies (9 and 10 sec pulses or to continuous ones). They consistently walked away from spinach odors, irrespective of the pulsing regime except at 1 sec pulses that did not elicit orientation. We further explored odor intensity on orientation towards maize odors by adjusting the odor stream intensity. At higher intensity (60 ml/min), the direction reversal started at the 6 sec half period, while at lower intensity (20 ml/min), it showed up only for the continuous stimulus. ECB larvae exhibit a striking ability to lock on to a direction, which they maintained despite gaps of up to 10 sec in the odor stream. Our results demonstrate that ECB neonate larvae express innate orientation preferences towards natural odors from plants. These reactions correlate well with the biological value of these plants for ECB: maize generally is accepted by ECB larvae and adults, while spinach represents a poor host because it produces (non-volatile) phytoecdysteroids that are toxic and deterrent.

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The effects of 3-octylthio-1,1,1-trifluoropropan-2-one (OTFP), a trifluoromethyl ketone that inhibits antennal esterases, on male Mamestra brassicae responses to the main pheromone component have been investigated using an actograph. This actograph used a movement detector based on the Doppler effect. The signal from the detector was digitalized and analysed on a PC microcomputer to quantify male activity. When added to the air flowing through the observation chamber, OTFP inhibited the responses of male moths to the pheromone. The number of males responding to the pheromone and the intensity of the response were decreased by OTFP. The latency of the response was increased and its duration decreased. These effects on the kinetics of the behavioural response cannot be directly correlated to the inhibition of pheromone catabolism by OTFP and other targets must be involved. The high level of inhibition of behaviour observed in presence of OTFP demonstrates the interest of trifluoromethyl ketones as mating disruption agents for pest control.

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A portable electroantennogram (EAG) sensor was used to measure relative atmospheric pheromone concentration in forest plots treated with aerial and ground applications of gypsy moth, Lymantria dispar (L.) (Lep., Lymantriidae), mating-disruption formulations. Five treatments (Disrupt II flakes with sticker, Disrupt II flakes without sticker, Disrupt II flakes in a sticker slurry, microcapsules and hand-applied Luretape), all applied at 75 g active ingredient per hectare and an untreated control were evaluated. Gypsy moth male catch in pheromone-baited traps and fertilization of deployed females were suppressed in all treatments, and no females deployed in treated plots produced more than 5% fertile eggs. Relative pheromone concentrations were significantly higher in the two treatments in which flakes were aerially applied with sticker and in the microcapsule treatment. Pheromone concentration measurements in the flakes without sticker and hand-applied treatments were not significantly different from those in the control. Mating success was negatively correlated with relative pheromone concentration. The ability of the EAG to detect differences in pheromone concentration that are correlated with mating success suggests that this could be a useful method for predicting the effectiveness of mating-disruption treatments.