Dispersal capacity in the Mediterranean corn borer, Sesamia nonagrioides

Corn (Zea mays L.) borers are the primary target of Bacillus thuringiensis Berliner (Bt) transgenic maize. Management of corn borer resistance to Bt requires information on larval and adult dispersal capacities, a feature that is particularly unknown in Sesamia nonagrioides Lefèbvre (Lepidoptera: Noctuidae), the most damaging corn borer in Spain. Larval dispersal was studied over a 3 year period by infesting plants with egg masses and dissecting the neighbouring plants 7, 14, and 32 days later to measure larval dispersal at several ages. The number and age of larvae were recorded in the dissected plants. Only mature larvae dispersed in significant numbers; they moved at least to rows adjacent to those containing the infested plant, and down the row five plants. The percentage of larvae that dispersed from the infested plant was density‐dependent. Adult dispersal was studied with directional light and pheromone uni‐traps over 5 and 3 year periods, respectively. Directional light traps were placed in the margins between Bt and non‐Bt maize fields, half oriented towards each of the two kinds of maize field. Pheromone traps were placed in the Bt and non‐Bt fields at increasing distances (0–100 m) from the border. The numbers of males and females caught in directional light traps were not different in traps oriented towards Bt or non‐Bt fields, but the number of males caught in the third flight in Bt fields was lower than in non‐Bt fields. These results suggest that males from adjacent Bt and non‐Bt fields mate indiscriminately with females emerging in any of the two kinds of maize fields. However, male movement in the third flight may not be sufficient to randomly distribute males between the two fields.     

From dusk till dawn: camera traps reveal the diel patterns of flower feeding by hawkmoths

1. Diel rhythms of foraging activity by animal flower visitors can reflect niche partitioning and are considered an important component of selection on floral traits. However, it has been notoriously difficult to obtain objective information on the patterns of flower visitation by crepuscular and nocturnal insects. 2. Motion-activated cameras were used for field-based studies of hawkmoth foraging behaviour on six African plant species. 3. The results showed that short-tongued hawkmoth species forage mainly around dusk and then sporadically throughout the night, whereas long-tongued hawkmoth species feed consistently throughout the night, with a peak shortly before midnight. 4. These results provide the first quantitative estimates of diel patterns of interactions between multiple hawkmoth and plant species and, when combined with qualitative reports from other studies, suggest that differences in diel activity between the two main hawkmoth functional groups (short- and long-tongued) are consistent across the Old and New Worlds.     

A comparative study of sex pheromone reception in the Hadeninae (Lepidoptera: Noctuidae)

Abstract A comparative study of the olfactory responses to pheromone compounds was performed in twenty-four species of Hadeninae. Electroantennograms (EAG) were recorded on male moths in response to thirty compounds and the response profiles of each species were analysed by factorial correspondence analysis. A limited number of molecules were found active and the most effective stimuli were Z9 tetradecenes and Z11 hexadecenes. The species of the Mythimna genus were most sensitive to aldehydes. Tholera decimalis did not respond to any of the molecules tested. The species belonging to the Mamestra and the Orthosia genera responded to a variety of molecules and no simple correlation was found between the genus and the EAG sensibility. Pheromone reception is discussed in relation to the taxonomy and the evolution of olfactory communication in Hadeninae.     

Downwind migration of the African army worm moth, Spodoptera exempta, studied by mark-and-capture and by radar

Abstract. 1. About 166,000 African armyworm moths, Spodoptera exempta (Walk.), were marked at an emergence site near Nairobi when they fed at night on trees baited with dyed molasses.
2. Six marked moths were captured in pheromone traps, including one at 90 km after flying for only one night, and another at 147 km.
3. Moth flight trajectories deduced from radar and from marking showed that migration was downwind.
4. During migration, moths become dispersed; hence the high densities that lead to outbreaks must be produced by concentration.
5. Some moths were ready to mate on the same night they completed their long-distance flight.     

Response of the egg parasitoid Trichogramma pretiosum to the sex pheromone of its host Heliothis zea

This paper presents results of olfactometer experiments with the egg parasitoid Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) and its host the corn earworm moth, Heliothis zea (Boddie) (Lepidoptera: Noctuidae). The sex pheromone of the host significantly reduced the total number of border crossings between odour fields in the olfactometer. Also, female parasitoids made significantly more visits to the calling moth odour field than to the opposite control field in the olfactometer. Further, the wasps spent significantly more time in the olfactometer field containing the sex pheromone released by calling virgin moths, than in control fields. If non-calling virgin moths were used as odour source, the response was reversed and wasps were repelled by the odour of the moths, and the numbers of visits were evenly distributed over the four flow fields. These results are discussed in the context of foraging ecology of egg parasitoids.

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Résumé Des expériences menées en olfactométrie avec le parasite oophage Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) et son hôte, Heliothis zea (Boddie) (Lepidoptera: Noctuidae) donnent les résultats suivants. La présence de la phéromone sexuelle de l'hôte réduit de façon significative le nombre de passages entre les champs odorisés. De mème, les parasites visitent plus fréquemment le champ qui dispense l'odeur de la femelle en appel que le champ témoin placé à l'opposé. Par ailleurs, le temps passé dans le champ qui contient la phéromone sexuelle émise par les femelles vierges en appel est significativement supérieur à la durée de visite des champs témoins. Si l'on utilise comme source d'odeur des femelles vierges qui ne sont pas en appel, la réponse est inversée, les parasites sont alors repoussés par l'odeur de ces papillons et le nombre de visites est distribué de façon aléatoire entre les quatre champs. Ces résultats sont discutés dans le contexte de l'écologie du comportement de recherche chez les parasites oophages.

     

Detoxification of naturally occurring chromenes in larvae of the generalist herbivore Spodoptera littoralis (Noctuidae)

Five naturally occurring chromenes from the Asteraceae including the insecticidal compounds precocene II (1) and encecalin (2) were administered to last instar larvae of Spodoptera littoralis via the food or by topical contact. Metabolites formed and excreted via the frass were analysed by GC-MS and by direct comparison with reference compounds obtained by partial synthesis. In total 28 different metabolites were identified, many of them reported here for the first time. All metabolites detected originated from phase I reactions (most probably catalysed by Cytochrom P-450-dependent monooxygenases) by hydroxylation, demethylation or reduction of the parent chromenes. The resulting metabolites can be regarded as detoxification products based on previous structure-activity studies. The increased polarity of the metabolites will furthermore facilitate their excretion by the larvae compared to the more apolar parent chromenes. The largest number of metabolites (eight for each compound) was detected following oral treatment with precocene II and encecalin respectively. 3-Monool as well as 3,4-trans-diol derivatives predominated in the frass of larvae treated with the latter compounds whereas the 6-hydroxyethyl derivatives were the major metabolites of the other chromenes investigated. The patterns of metabolites originating from precocene II or encecalin were the same following oral application or topical treatment.     

The effects of unilateral antennectomy on the flight behaviour of male Heliothis virescens in a pheromone plume

Abstract .Unilaterally antennectomized Heliothis virescens (F.) males flying close to the central axis of a plume of sex pheromone display no significant differences in behaviour compared to sham-operated males in course angles, track angles, airspeed and groundspeed. This demonstrates that right/left antennal information is not necessary for normal orientation movements in response to pheromone, but rather that it is 'blended' within the moth's central nervous system before pheromone-mediated manoeuvres are made. However, some unilaterally antennectomized moths (36%) make repetitive, asymmetrical, saw-tooth-shaped tracks during pheromone-mediated upwind progress, whereas control moths never make such tracks. Unilaterally antennectomized moths made such tracks on the side of the plume contralateral to the missing antenna. We hypothesize that these occasional asymmetrical tracks in unilaterally ablated males are the result of reiterative asymmetrical pheromone stimulation of a higher probability on track legs going toward rather than away from the long axis of the plume on males with a single antenna remaining on the 'away from axis' side. Combined with a greater propensity for treated moths to lock onto the plume away from the central axis on one side rather than the other, repetitive successive asymmetrical track legs (resulting in a saw-tooth-shaped track) are commonly observed in these moths. Control moths do also make asymmetric successive track legs but they rarely are repeated and thus are not readily observed.     

Comparison of pheromone trap design and lures for Spodoptera frugiperda in Togo and genetic characterization of moths caught

Fall armyworm, Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae), is a pest of grain and vegetable crops endemic to the Western Hemisphere that has recently become widespread in sub‐Saharan Africa and has appeared in India. An important tool for monitoring S. frugiperda in the USA is pheromone trapping, which would be of value for use with African populations. Field experiments were conducted in Togo (West Africa) to compare capture of male fall armyworm using three commercially available pheromone lures and three trap designs. The objectives were to identify optimum trap × lure combinations with respect to sensitivity, specificity, and cost. Almost 400 moths were captured during the experiment. Differences were found in the number of S. frugiperda moths captured in the various trap designs and with the three pheromone lures, and in the number of non‐target moths captured with each lure. The merits of each trap × lure combination are discussed with respect to use in Africa. A nearly equal number of COI‐CS (161) and COI‐RS (158) moths was captured with no differences found in COI marker proportions among traps or lures. However, the diagnostic rice strain marker Tpi was rarely found. Overall, the genetic characterization of the pheromone trap collections indicated a consistent distribution of genetic markers from 2016 to 2017, suggesting a population at or near equilibrium.