Alarm pheromones and chemical communication in nymphs of the tropical bed bug Cimex hemipterus (Hemiptera: Cimicidae).

The recent resurge of bed bug infestations (Cimex spp.; Cimicidae) and their resistance to commonly used pesticides calls for alternative methods of control. Pheromones play an important role in environmentally sustainable methods for the management of many pest insects and may therefore be applicable for the control of bed bugs. The tropical bed bug, Cimex hemipterus, is a temporary ectoparasite on humans and causes severe discomfort. Compared to the common bed bug, Cimex lectularius, little is known about the chemical signalling and pheromone-based behaviour of the tropical species. Here, we show that the antennal morphology and volatile emission of C. hemipterus closely resembles those of C. lectularius and we test their behavioural responses to conspecific odour emissions. Two major volatiles are emitted by male, female and nymph C. hemipterus under stress, (E)-2-hexenal and (E)-2-octenal. Notably, nymph emissions show contrasting ratios of these compounds to adults and are further characterized by the addition of 4-oxo-(E)-2-hexenal and 4-oxo-(E)-2-octenal. The discovery of this nymph pheromone in C. hemipterus is potentially the cause of a repellent effect observed in the bio-tests, where nymph odours induce a significantly stronger repellent reaction in conspecifics than adult odours. Our results suggest that pheromone-based pest control methods developed for C. lectularius could be applicable to C. hemipterus, with the unique nymph blend showing promising practical properties.

Nymphs of the common bed bug (Cimex lectularius) produce anti-aphrodisiac defence against conspecific males.

BACKGROUND: Abdominal wounding by traumatic insemination and the lack of a long distance attraction pheromone set the scene for unusual sexual signalling systems. Male bed bugs (Cimex lectularius) mount any large, newly fed individual in an attempt to mate. Last instar nymphs overlap in size with mature females, which make them a potential target for interested males. However, nymphs lack the female's specific mating adaptations and may be severely injured by the abdominal wounding. We, therefore, hypothesized that nymphs emit chemical deterrents that act as an honest status signal, which prevents nymph sexual harassment and indirectly reduces energy costs for males. RESULTS: Behavioural mating assays showed that males mount nymphs significantly shorter time compared to females, although initial mounting preference was the same. In support of our hypothesis, nymphs experienced the same percentage of mating with sperm transfer as females if they were unable to emit (E)-2-hexenal, (E)-2-octenal 4-oxo-(E)-2-hexenal and 4-oxo-(E)-2-octenal, from their dorsal abdominal glands. We report that the aldehydes and 4-oxo-(E)-2-hexenal are detected by olfactory receptor neurons housed in smooth and grooved peg sensilla, respectively, on the adult antennae, at biologically relevant concentrations. Behavioural experiments showed that application of 4-oxo-(E)-2-hexenal or the two aldehydes at a nymph-emitted ratio, to a male/female pair during mounting initiation, decreased mating frequency to a rate comparable to that of a male/nymph pair. CONCLUSIONS: By combining behavioural and sensory studies, we show that the nymph-specific alarm pheromone plays an important role in intra-specific communication in the common bed bug. Alarm pheromones are commonly looked upon as a system in predator/prey communication, but here we show that alarm pheromones may be used as multipurpose signals such as decreasing the risk of nymphal mating by males.

Characterization of the antennal olfactory system of the bed bug (Cimex lectularius).

The common bed bug Cimex lectularius (Hemiptera; Cimicidae) is a temporary ectoparasite on humans that is currently reinvading the developed countries. Like other haematophagous arthropods, host seeking and orientation in C. lectularius is partially mediated by olfaction. In this study, we reconfirmed the distribution of the 44 olfactory sensilla and identified 3 different sensillum types located at the distal tip of C. lectularius antenna by external morphology mapping. Using a panel of relevant odorants previously reported to be bioactive in various haematophagous arthropods, we correlated the morphological mapping with an electrophysiological characterization of the olfactory receptor neurons housed in each specific sensillum. We found that all 9 grooved peg sensilla responded specifically in a dose-dependent manner to ammonia, whereas (E)-2-hexenal, (E)-2-octenal, dimethyl trisulfide, 6-methyl-5-hepten-2-one, alpha-pinene, indole, and ethyl butyrate evoked dose-dependent responses within the 6 smooth peg sensilla. Based on the pattern of response to the tested compounds, we were able to separate the 6 smooth peg sensilla of the bed bug into 3 distinct functional classes. We compare our results with previous electrophysiological recordings made with these compounds on other haematophagous arthropods.

Do anthropogenic transports facilitate stored-product pest moth dispersal? A molecular approach.

Stored-product moths cause large economic damage in food processing industries and storage facilities. Control of indoor pests is currently dealt with locally, and control strategies seldom include different mills or cooperative industries in joint efforts to reduce infestations. In colder climates where conditions hinder flight dispersal of stored-product moths, we hypothesize that human transport between mills will facilitate dispersal. Albeit considered intuitive, this hypothesis has so far never been tested. Male moths from three mills (populations) in southern Sweden and Denmark were collected and by using amplified fragment length polymorphism (AFLP) pair-wise F(st) values were calculated. Cluster (population) origins of the genotypes were computed by using a model-based method, structure. The results suggest that known transportation of flour between two mills generate genetically more similar populations of the economically important stored-product moth, Ephestia kuehniella (Zell.) (Lepidoptera; Pyralidae), compared to the third mill, with another distribution area, but situated geographically in between the other mills. The structure model placed the sampled genotypes to belong to either two or five original populations, with a higher probability of two original populations. The third mill was consistently different from the other two mills independent of the models' calculated number of populations. Although the study was restricted to three mills and one transportation route, it highlights the possibility that transportation of food products promotes genetic mixing (i.e. dispersal) of insect pest populations. Including cooperating mills in control (or monitor) strategy schemes against stored-product pest insects would therefore be a more effective action, rather than to treat each mill separately.

Evaluation of long-term mating disruption of Ephestia kuehniella and Plodia interpunctella (Lepidoptera: Pyralidae) in indoor storage facilities by pheromone traps and monitoring of relative aerial concentrations of pheromone.

The potential for pheromone-based mating disruption (MD) of Ephestia kuehniella (Walker) and Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) was investigated in two flour mills and a pet food distributor. Plastic sachets emitting 2-3 mg per d (Z,E)-9,12-tetradecadienyl acetate, the major pheromone component of both moth species, were used as MD dispensers, which were applied in grid systems resulting in one dispenser per 100 m(3) of air volume. Pheromone traps with sticky inserts were used to monitor moth population fluctuations. To monitor pheromone levels in the air before, during, and after the treatment, electroantennographic (EAG) measurements were performed using a portable device. All localities showed decreased trap catches after application of MD. In two localities with low initial population densities, trap catches were reduced immediately after application of MD and remained very low, even several months after the MD treatment was terminated. In contrast, in a locality with a higher initial population density the reduction in trap catches was slower, and trap catches increased again soon after the termination of the MD treatment. Electrophysiological data showed not only increased aerial levels of pheromone during the treatment period but also levels that were higher than during pretreatment, even 12 mo after removal of MD dispensers. The localities had good ventilation, and the memory effect observed indicates that the pheromone adhered to surfaces that subsequently functioned as secondary dispensers. Customer complaints registered by one of the mills were 49% less in 2004, after 2 yr of MD compared with 2002, the year before the treatments began.

Reduction in an almond moth Ephestia cautella (Lepidoptera: Pyralidae) population by means of mating disruption.

Pheromone-based mating disruption of the almond moth (Ephestia cautella) (Walk.) (Lepidoptera: Pyralidae) was carried out in a chocolate factory in Sweden. Population monitoring was conducted with pheromone-baited traps and water traps. Pheromone traps showed a 94% catch reduction, and monitoring with water traps showed a significant decrease in total catch (5.0 and 1.6 individuals per trap per week before and during treatment respectively). The significance of the results was tested by fitting the observed data to a first-order autoregressive model. This made it possible to test the data with a 95% confidence interval, comparing trap catches before mating disruption treatment with trapping data during the experiment. It is suggested that this statistical approach may be used more frequently in mating disruption experiments where it is extremely difficult to control external factors and therefore equally difficult to use a comparable control plot to evaluate the treatment.

Dietary glycerol and adult access to water: effects on fecundity and longevity in the almond moth.

The quality of food eaten by larval insects will affect traits such as gamete production, fat reserves, muscle bulk and body size in the adult. Moreover, larvae also depend on high moisture content in the diet for survival. The almond moth (Ephestia cautella) (W.) (Lepidoptera; Pyralidae) does not feed as an adult although it continues to drink water. We tested the idea that an almond moth could compensate for a low-water diet as a larva by increasing its water intake as an adult. We reared larvae on two different food sources with different moisture regimes; standard laboratory diet with glycerol (relatively wet) and standard diet without glycerol (relatively dry). Half the adult moths from each treatment were given water to drink before their first and only mating. Our results show that wet larval diets (i.e. containing glycerol) significantly decreased fecundity (total number of eggs laid and the proportion of hatched larvae), whilst it significantly increased male and female longevity. The interaction effect of water access for adult males and females was significant, independent of the glycerol in the larval diet. Longevity in females that were not presented with water as adults was slightly higher if mated with a male that had had access to water, suggesting a mating donation of water. However, females that received water as adults showed a decreased longevity if mated with a male who had also had access to water as an adult, indicating a negative effect of water if received by both males and females. In addition, when the larval diet included glycerol, increased number of eggs laid decreased female longevity, whilst an absence of glycerol in the larval diet resulted in low female longevity that was unlinked with fecundity. Glycerol is used in many artificial insect diets and the fact that it shows a strong effect on key life-history traits (reproductive output and longevity in this species), merits careful re-examination of its effects on these important traits in other laboratory models. We also discuss the possibility that larval diet can affect female reproductive decisions.

Heritable variation of sex pheromone composition and the potential for evolution of resistance to pheromone-based control of the Indian meal moth, Plodia interpunctella.

The short-term evolutionary effect of pheromone-based mating disruption on the mating ability of the Indian meal moth, Plodia interpunctella, was investigated. Three independent selection lines were established, and the mating ability of moths in plastic tents treated with high doses of pheromone and in control tents was compared for two consecutive generations. In addition, the heritability of the sex pheromone blend, measured as the ratio of two major pheromone components (Z,E)-9,12-tetradecadienyl acetate and (Z,E)-9,12-tetradecadienol, was estimated. Based on a mother-daughter regression analysis including 21 families, the heritability of the pheromone blend was 0.65 +/- 0.14, indicating a potential for evolutionary change of the character. However, no increase in mating ability of females in pheromone-treated tents or alteration of the pheromone blend was observed in any selection line when compared with control lines, indicating no or weak selection on the pheromone blend as well as other traits influencing mating ability of this species under the created mating disruption conditions. Factors contributing to the lack of selection effects are discussed.