Hermann Zacharias 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.

Chirality determines pheromone activity for flour beetles

Olfactory perception and orientation behaviour of female and male flour beetles (Tribolium castaneum, T. confusum) to single stereoisomers of their aggregation pheromone revealed maximal receptor potentials and optimal attraction in response to 4R,8R-(−)-dimethyldecanal, whereas its optical antipode 4S,8S-(+)-dimethyldecanal was found to be inactive in this respect. Female flour beetles of both species were ≈ 103 times less attracted to 4R,8S-(+)- and 4S,8R-(−)-dimethyldecanal than to 4R,8R-(−)-dimethyldecanal, while male flour beetles failed to respond to the R,S-(+)- and S,R-(−)-stereoisomers. Pheromone extracts of prothoracic femora from unmated male flour beetles elicited higher receptor potentials in the antennae of females than in those of males. The results suggest that the aggregation pheromone emitted by maleT. castaneum as well as maleT. confusum has the stereochemical structure of 4R,8R-(−)-dimethyl-decanal, which acts as sex attractant for the females and as aggregant for the males of both species.

The defensive role of alkaloids in insects and plants

The term alkaloid ( = alkali-like) is applied in a rather loose sense to denote naturally occurring organic compounds containing nitrogen (mostly in ring structures) and thus displaying basicity. According to their biosynthesis, the majority of these compounds can be regarded as derivatives of certain amino acids, viz. lysine, ornithine, phenylalanine, tryptophane and tyrosine, while terpenoid, steroid and other precursors are incorporated into their carbon skeletons. Many phytoalkaloids (about 3000 different ones are known so far) occur dissolved as cations in plant sap, and on evaporation of the former, they react with available organic acids to form salts which subsequently are deposited in vacuoles rather than in the protoplasm. Moreover, they tend to accumulate in the peripheral parts (bark, leaves, fruit) which can be shed. The alkaloids may thus be regarded as excretory products or so-called secondary substances which are offshoots from the primary metabolic pathways. Most of the alkaloids exert in various animals a more or less specific action upon different regions of their nervous system 1. The cholinomimetic alkaloids may be subdivided into compounds which act preferentially on postsynaptic neurone receptors, the neuromuscular junction as well as the receptors of secretory glands. Other alkaloids act primarily by blocking the acetylcholine receptors and influence autonomic effector cells rather than ganglion cells (e.g. tropane alkaloids). Inhibitors of cholinesterase cause accumulation o f acetylcholine and therefore continuous stimulation of cholinergic receptors (e.g. physostigmine). The sympathomimetic compounds are either releasers of noradrenaline (e.g. tyramine, ephedrine, Rauwolfia alkaloids), inhibitors of its readsorption (e.g. cocaine) or act as adrenergic blocking agents (yohimbine, ergot alkaloids). Colchicine and the Vinca alkaloids are known to inhibit the incorporation of uridine into RNA. The Veratrum alkaloids cause repetitive discharges of nerve cells, apparently by delaying repolarization (possibly by action on lipid components and an ATPase in the cell membrane).

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.

Possibilities of using insectistatics and pheromones in pest control

Agents that can decimate insect populations by suppressing growth and reproduction rather than by causing rapid mortality are called insectistatics. Their activity includes interruption of cuticle formation, induction of hormonal imbalance by extrinsic juvenoids or ecdysoids, developmental disturbances due to nutrient antagonists, symbioticides, or accelerators of metabolism. Disruption of mating may be accomplished by pheromone trapping and disorientation or by prevention of sex attraction. The possible contribution of such biotechnical procedures to the control of storage pests is discussed.

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.