Anna R. Levinson

Structure of sensilla, olfactory perception, and behaviour of the bedbug, Cimex lectularius, in response to its alarm pheromone

Abstract When deprived of the terminal antennal segments, male and female bedbugs failed to respond to their alarm pheromone and to their assembling scent. Trans-oct-2-en-1-al or trans-hex-2-en-1-al, being the major constituents of the former, induce in adults and larvae of Cimex lectularius a typical alarm behaviour resulting in dispersal of assembled bedbugs; the rapidity of escape depends on the aldehyde concentration in the air. The behavioural threshold for adults is about 9×1014 molecules of trans-oct-2-en-1-al or 6×1015 molecules of trans-hex-2-en-1-al per ml air. The distal part of the terminal antennal segment of C. lectularius reveals the following sensilla: bristles (type A1), immersed cones (type B1), plates (type B2), grooved pegs (type C), smooth pegs (type D), hairs with even (type E1), and uneven wall thickness (type E2). The number and distribution of these sensilla is relatively constant and similar in both sexes, but differs slightly in neonate larvae. The pegs and hairs of types C, D, E1 and E2 were shown to have porous walls, a prerequisite for olfactory function. Receptor potentials were recorded from olfactory sensilla of types E1 and E2 after stimulation with trans-hex-2-en-1-al and trans-oct-2-en-1-al. The minimal concentration of trans-hex-2-en-1-al evoking a receptor potential is about 2×1010 molecules per ml air. The above olfactory sensilla were found to respond also to hexan-1-al, but almost no responses to pentan-1-al, butan-1-al, trans-hex-2-ene, and trans-oct-2-ene were observed. A minimum chain length of six carbons atoms and a terminal carbonyl group are molecular prerequisites for optimal odorant activity, while the presence of a Δ2-double bond is not essential for stimulation of the alarm pheromone receptors of the bedbug.

Poropak-Q collection of pheromone components and isolation of (Z)-and (E)-14-methyl-8-hexadecenal, sex pheromone compo nents, from the females of four species of Trogodernw (Coleoptera: Dermestidae)

A major sex pheromone component of each of fourTrogoderma species was isolated by aeration of the female beetles and absorption of the volatiles on Porapak-Q. (Z)-14-Methyl-8-hexadecenal was identified as the major component inT. inclusum andT. variabile, and (E)-14-methyl-8-hexadecenal was identified inT. glabrum. Both (Z)- and (E)-14-methyl-8-hexadecenal were found inT. granarium (Khapra beetle), in the ratio 92Z∶8E. In laboratory bioassays, male beetles exhibited arousal and mating responses to the aldehydes, and could discriminate between the geometric isomers. The daily production of the aldehyde was calculated for each species, and other active components were detected. These aeration-absorption studies contrast with earlier studies on macerated beetles, in which the aldehyde was not detected. The efficacy of the aeration-absorption system for collection of the sex pheromones is also described. The absorbent (Porapak-Q) efficiently collected the active pheromone; only minor amounts of activity were left in the other parts of the system.

Synthesis and biological activity of both (E)- and (Z)-isomers of optically pure (S)-14-methyl-8-hexadecenal (trogodermal), the antipodes of the pheromone of the khapra beetle

Abstract Both ( E )- and ( Z )-isomers of ( S )-14-methyl-8-hexadecenal (trogodermal) were synthesized from 100% optically pure ( R )-(+)-citronellic acid. These antipodes of the khapra beetle pheromone were 1/500 to 1/1000 times as active as the natural ( R )-pheromone. Determination of the optical purities of citronellic acid and related compounds was achieved by hplc method. Warning was made not to forget the measurement of density in expressing the optical rotation of a neat liquid as [α] D (neat).

Dried seeds, plant and animal tissues as food favoured by storage insect species

The nutritional preferences of storage insects are evaluated from the viewpoint of feeding habits, composition and utilization of foodstuffs as well as the involvement of attractants and feeding stimulants. On the basis of their feeding habits, coleopterous species infesting stored produce may be divided into four major groups: (a) Species which in the larval and adult stage consume dried foodstuffs from plant sources (e.g., Sitophilus granarius), (b) Species which in the larval and/or adult stage consume dried foodstuffs of plant and animal origin (e.g., Oryzaephilus surinamensis, Cryptolestes ferrugineus, Tenebroides mauretanicus), (c) Species which feed on material of animal origin in the larval stage and feed on nectar and pollen as adults (e.g., Attagenus pellio), (d) Species feeding on material of animal origin as larvae and adults (e.g., Dermestes maculatus). Most lepidopterous species (except for Hofmannophila pseudospretella) feed only in the larval stage on stored seeds and other plant tissues.

Pheromone biology of the tobacco beetle (Lasioderma serricorne F., Anobiidae) with notes on the pheromone antagonism between 4S,6S,7S-and 4S,6S,7R-serricornin

Attraction and copulation of male tobacco beetles (Lasioderma serricorne F.) are mediated by pheromonal as well as tactile stimuli, and mating consists of a relatively short courtship (male mounting the female) and long pairing stage (in end to end position). The gland producing the sex pheromone is attached to the apex of an apodeme within the second abdominal segment of the female. The antenna of male L. serricorne has a serrated flagellum (˜708 urn) being equipped with short (14–17 urn) and long (20–23 urn) bristles as well as short (3.9–4.4 urn) and long (5.3–6.3 μm) sensilla basiconica, scattered among the former.

Olfactory behavior and receptor potentials of the khapra beetleTrogoderma granarium (Coleoptera: Dermestidae) induced by the major components of its sex pheromone, certain analogues, and fatty acid esters

On the basis of the antennal receptor potentials and the extent of attraction and copulation induced in unmated male khapra beetles, (Z)- and (E)-14-methyl-8-hexadecenal were recognized as the most important components of the pheromone system of femaleTrogoderma granarium (Everts), and were named (Z)- and (E)-trogodermal. Air blown over 10−5 to 10−4 μg of (Z)-trogodermal produced receptor potentials equivalent to that elicited by one virgin femaleT.granarium, while ∼10−2 μg of (Z)-trogodermal was required to cause complete attraction and copulation of unmated males. (Z)-Trogodermal was about 10 times more active than (E)-trogodermal. (Z)-8-Hexadecenal was ∼10−2 times less effective than (Z)-trogodermal in causing attraction and 104 time less active in stimulating copulation. (Z)- and (E)-14-methyl-8-hexadecen-1-ol and methyl (Z)- and (E)-14-methyl-8-hexadecenoate displayed a relatively low activity for unmated male khapra beetles. Methyl and ethyl oleate, ethyl linoleate, ethyl palmitate, and ethyl stearate were less effective than (Z)-trogodermal by 6–8 orders of magnitude and are nonspecific attractants. The intensity of response to a particular compound was consistent when assessed by the essential components of mating behavior: receptor potentials, attraction, and copulation.

Perception by Trogoderma species of chirality and methyl branching at a site far removed from a functional group in a pheromone component

Responses to enantiomers of (Z)- and (E)-trogodermal (14-methyl-8-hexadecenal) suggest that fourTrogoderma species utilize the (R)-(−) configuration at C-14. Removal of the C-14 methyl branch decreased the response. These results demonstrate the high specificity associated with the configuration at a chiral center, or the methyl branch, distant in terms of numbers of bonds from a functional group.

Pheromone biology of the Mediterranean fruit fly (Ceratitis capitata Wied.) with emphasis on the functional anatomy of the pheromone glands and antennae as well as mating behaviour

In calling males of Ceratitis capitata Wied. (Dipt., Trypetidae), the sex pheromone is released from the anal glands through ducts to the surface of the expanded anal ampulla. The epithelium of the anal glands of sexually mature males comprises ramified as well as columnar cells, of which the former are likely to secrete the pheromone. The anal gland cells of newly emerged males are undifferentiated and fail to produce pheromone. Within the first week of adult life the pheromone level increases steeply, whereupon it remains relatively high until senescence.

Orange-derived stimuli regulating oviposition in the Mediterranean fruit fly

Abstract:  Some visual and olfactory host stimuli influencing oviposition of the Mediterranean fruit fly (Ceratitis capitata Wiedemann) in orange fruit were investigated in a laboratory‐reared strain of this species. Mated females of C. capitata were found to be attracted to the same extent by fragrant orange fruits and odourless sham oranges, while unmated females were notably less attracted than mated females by the above objects. Mated females laid significantly more eggs in orange‐coloured than in whitish (optically neutral) spherical wax dummies (diameter, 9.0 cm) as well as in both orange‐coloured and whitish wax dummies supplemented with high internal humidity (80–100%) compared with respective wax dummies supplied with low internal humidity (30–50%). The orange‐like colour together with high internal humidity provides basic stimuli supporting adequate oviposition of C. capitata in oranges. The oviposition rate of female C. capitata was not significantly changed when graded dosages ranging from 0.004 to 19.6 μl of orange peel oil per cm2 were added to orange‐coloured wax dummies, while oviposition was considerably subdued by addition of 3.9 μl orange peel oil and completely disrupted by addition of 9.8 or 19.6 μl of orange peel oil per cm2 of whitish wax dummies. Oviposition of C. capitata in ripe orange fruit may thus be interpreted by the predilection of this tephritid species for an orange‐coloured, glossy pericarp, being capable of counteracting the deterrent effect of the essential oil found in orange flavedo.

Reflections on structure and function of pheromone glands in storage insect species

Several polyphagous coleopteran and lepidopterous species, presently known as “storage insects”, have presumably evolved from free-living ancestral species, being capable of growth and reproduction on stored, desiccated and often nutritionally deficient foodstuffs. These potentially harmful insect species have probably adapted themselves to the newly acquired storage biotope by means of a well-developed sensory equipment serving food acquisition, aggregation and mate finding.Information by molecules may be communicated among the individuals of an insect species by means of relatively volatile pheromones (Greek, pherō=convey) being emitted by exocrine glands and mainly carried by moving air to the sensilla of responsive individuals, or among the internal organs of an insect by means of relativelynonvolatile hormones (Greek, hormaō=impel), secreted fromendocrine glands and transported by the haemolymph to the receptors of target organs. It was postulated that pheromones were among the first chemical messengers utilized during evolution of animal behaviour, and that the pheromones of primitive protozoans could have been precursors of the hormones of metazoans. Hormones of the neurosecretory cells and corpora allata were found to induce sex pheromone biosynthesis in femaleTenebrio molitor, while dietary intake of a juvenile hormone analogue was shown to significantly enhance the production of aggregation pheromones in the males of certain silvanid and cucujid species.Aggregation pheromones are usually produced by the longlived and feeding males of several coleopteran species (Table 2) which deposit those chemical messengers to the substrate, where they induce the formation of bisexual assemblies supporting feeding, mating and reproduction. Sex pheromones are mostly produced by the short-lived and non-feeding females of several coleopteran and lepidopterous species (Table 2); females of those species usually release their sex pheromones to the air space during calling, and thus attract conspecific males for mating (Fig. 5 a–c).In some dermestid species, pheromone emission differs from the above scheme. Females of the short-lived and non-feedingTrogoderma granarium andT. inclusum release a phromone acting as a sex attractant for conspecific males and—in synergistic combination with tactile stimuli—as an assembling scent for conspecific females (Figs. 1 a, b, 2 and Table 1), females of the short-lived and feedingAntbrenus verbasci, Attagenus megatoma andAtt. elongatulus produce a sex pheromone for conspecific males, while females of the long-lived and feedingAn. scrophulariae emit a sex pheromone which lures conspecific males.Males of the long-lived and non-feeding bruchid speciesAcanthoscelides obtectus release a sex pheromone which attracts conspecific females. Androconial pheromones are discharged during courtship from the alar scales and abdominal tufts found in males of several microlepidopteran species (Phycitidae) includingAnagasta kuebniella, Cadra cautella, Ephestia elutella andPlodia interpunctella (Fig. 6 b–c); those aphrodisiac pheromones are known to enhance the specific responsiveness of the females to their mates. Electrophysiological recordings revealed that aggregation pheromones elicit considerable receptor potentials in the antennal olfactory sensilla of both sexes, whereas sex pheromones induce high receptor potentials in the antennal olfactory sensilla of one sex only. It was assumed that aggregation pheromones may be the evolutionary precursors of sex pheromones.Pheromone-producingexocrine glands are essentially groups of modified epidermals cells which are found in different body regions of male and/or female storage insect species. A simple pheromone gland, consisting of a single layer of adjacent secretory cells beneath the endocuticle of the 5th visible abdominal sternite, occurs in femaleTrogoderma granarium (Fig. 3 a). A more complex design, comprising an intra-abdominal semiglobular pheromone gland with numerous secretory cells being connected to tubuli which lead to an invaginated cuticular cribellum, is available in maleDermestes maculatus (Figs. 3 c, d and 4 c). The cribellum, provided with a caudally curved brush of fluted brisles, occurs in the centre of the 4th visible abdominal sternite (Figs. 4 a, b and 7 b). An apodemous exocrine gland is found in the lumen of the second abdominal segment of femaleLasioderma serricorne (Fig. 3 b). This lobate gland comprises many secretory cells, being connected by numerous tubuli to a sheath-like conical duct enveloping a V-shaped skeletal apodeme, which terminates in the abdominal tip. In maleTribolium castaneum, the secretory cells of both pheromone glands are connected by tubuli to two cribella, being densely covered by fluted bristles, and found in the femora of both forelegs (Fig. 7 a). Females of the phycitid speciesAnagasta kuebniella, Cadra cautella, Ephestia elutella andPlodia interpunctella are equipped with an intersegmental pheromone gland, situated between the 8th and 9th abdominal segment near the genital opening. The exocrine gland of the four moth species consists of a single layer of columnar secretory cells, lined by a spongy cuticle which seems to be permeable to the sex pheromone (Fig. 6 a). The latter is disseminated by calling females (Fig. 5 a, b) while their exocrine glands are widely exposed. Males of the above phycitid species are furnished with alar and abdominal androconia which become exposed during courtship and discharge aphrodisiac pheromones. The base of each of the androconial bristles and scales is immersed to an underlying unicellular, pheromone-producing gland (Fig. 6 d, e). The aphrodisiac pheromones, being secreted by the above glandular cells, are passing the lumen and walls of the bristles and scales, and evaporate from the surface of the latter. For example, malePlodia interpunctella possess 2 pairs of scent tufts (a small and a large one) on both sides of the 8th abdominal tergiet as well as 2 pairs of scent tufts (a small and a large one) near the base of the costal margin of the forewings (Fig. 6 b, c). Females of several phycitid species respond to the aphrodisiac pheromone of conspecific males by a pronounced readiness to mate.In the course of time, about 3 dozens of insect species (⊃3/4 coleopteran and ⊃ 1/4 lepidopterous species) have undergone sympatric speciation by sharing desiccated food in stores as a common habitat. Fertile matings between such heterogeneous species are often prevented by morphological and anatomical incompatibilities as well as physiological and behavioural barriers. Most of the species living in the storage habitat are reproductively isolated due to the molecular structure and blend composition of their pheromones (Table 2). Interestingly, some species (listed below) deviate from the majority by sharing the structure of their main pheromone components (mentioned in parenthesis), and are thus poorly separated: the curculionidsSitophilus oryzae andS. zeamais ((4S,5R)-5-hydroxy-4-methyl-3-heptanone), the tenebrionidsTribolium castaneum andT. confusum ((4R,8R)-dimethyldecanal) as well as the dermestidsTrogoderma inclusum andT. variabile ((R,Z)-14-methyl-8-hexadecenal). Theinsufficient reproductive isolation of the above species is compensated, i.a., by additional availability of a sex pheromone in femaleTribolium confusum, by different calling periods and emission rates of (R,Z)-14-methyl-8-hexadecenal in females of the forementionedTrogodema species.Trogoderma glabrum andT. granarium areincompletely isolated by sharing (R,E)-14-methyl-8-hexadecenal as a pheromone component; they are indeed capable of cross-mating, but produce sterile hybrids. Moreover, maleOryzaepbilus mercator andO. surinamensis incorporate (Z,Z)-3,6-dodecadien-11R-olide as a common chiral component to their aggregation pheromones. The females of 5 phycitid species share (Z,E)-9,12-tetradecadien-1-yl acetate as their main pheromone component, while they are reproductively separated by additional emission of (Z)-9-tetradecen-1-yl acetate and (Z,E)-9,12-tetradecadien-1-ol as secondary pheromone components, by the production of different androconial pheromones in conspecific males as well as different circadian calling activities.In the course of their research engagement on pheromones of storage insect and mite species (during the past 2.5 decades), the authors enjoyed fruitful collaboration with several renowned investigators working in Athens, Berlin, Hamburg, New York, Pantnagar, Tiantsin, Tokyo, Wisconsin, Yokohama and Zürich (chapter 6).