Combination Insecticide Treatments with Methoprene and Pyrethrin for Control of Khapra Beetle Larvae on Different Commodities.

Trogoderma granarium Everts, the khapra beetle, is a serious pest of stored products throughout the world. Larvae pose a significant threat to stored products because they feed on >100 different commodities, possess the ability to enter facultative diapause, and are difficult to detect. Control methods for T. granarium include fumigation, contact insecticides, trapping, and insecticide-incorporated packaging. The objective of this study was to determine the residual efficacy of two insecticide formulations (methoprene + deltamethrin + piperonyl butoxide synergist Gravista® and methoprene + deltamethrin, DiaconIGR®Plus). These insecticides were evaluated on three stored product commodities, corn, wheat, and brown rice, by exposing T. granarium larvae during a 12-month testing period. Both formulations significantly reduced adult emergence on corn and wheat for 12 months and on brown rice for up to 6 months. Adult emergence was highest at month 12 for corn (8.41%), and brown rice (85.88%), and month 9 for wheat (39.52%), treated with DiaconIGR®Plus or Gravista®, respectively. A biological index used to measure the development of exposed larvae on the treated grain from the larval stage (low values) to adult emergence (high values) was lower (fewer adults) on corn and wheat compared to controls. Despite differences in formulations, each of these grain protectants could be utilized by stored commodity managers to protect commodities during storage and transportation for T. granarium when and if this pest is detected at USA ports of entry.

Disruption of semiochemical-mediated movement by the immature Trogoderma variabile Baillon and Trogoderma inclusum Le Conte (Coleoptera: Dermestidae) after exposure to long-lasting insecticide-incorporated netting.

BACKGROUND: Highly mobile stored product insects may be able to readily orient in response to food cues and pheromones to attack durable commodities at each link of the postharvest supply chain. A 0.4% deltamethrin-incorporated long-lasting insecticide-incorporated netting (LLIN) is a successful novel preventative integrated pest management (IPM) tactic to intercept dispersing insects after harvest. However, it is unknown whether exposure to LLIN may affect olfaction and orientation to important semiochemicals by immature stored product dermestids, therefore the aim of this study was to assess whether exposure to LLIN disrupts the normal olfactory and chemotactic behavior of warehouse beetle, Trogoderma variabile Ballion (Coleoptera: Dermestidae), and the larger cabinet beetle, T. inclusum Le Conte (Coleoptera: Dermestidae), larval movement in the presence of important semiochemicals, including food kairomones (e.g., flour) and pheromones, e.g., (Z)-14-methyl-8-hexadecenal. RESULTS: The distance moved by the larval population of T. variabile was reduced by 64% after 24-h exposure to LLIN compared to control netting but not immediately after exposure, while T. inclusum larvae movement was reduced by 50% after 24-h exposure to LLIN compared to the control netting. Generally, the olfaction and orientation of larval dermestids were affected after exposure to LLIN compared to control netting. There were species-linked differences in effects on olfaction after the insects were exposed to LLIN. CONCLUSION: Our study suggests the use of LLIN may enhance the effectiveness of other concurrent behaviorally-based strategies such as mating disruption when used as part of a comprehensive IPM program in the postharvest environment. © 2023 Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Comparison of different traps and attractants in 3 food processing facilities in Greece on the capture of stored product insects.

Certain lures are marketed toward particular pests or classes of pests, while others might be multi-species lures. Investigative aims for this study included both which trap was most sensitive and whether different combinations of traps and attractants were delivering novel information about the stored product insect community. Comparisons were made for all combinations of 3 commercial traps and 4 different attractants plus an untreated control on the capture of stored-product insects for 2 consecutive years in 3 food processing facilities in Central Greece. The traps used in the experiments were Dome Trap (Trécé Inc., USA), Wall Trap (Trécé) and Box Trap (Insects Limited, Ltd., USA). The attractants that were evaluated were 0.13 g of (i) PantryPatrol gel (Insects Limited), (ii) Storgard kairomone food attractant oil (Trécé), (iii) wheat germ (Honeyville, USA), and (iv) Dermestid tablet attractant (Insects Limited). The traps were inspected approximately every 15 days and rotated. A total of 34,000+ individuals were captured belonging to 26 families and at least 48 species. The results indicated that Indian meal moth, Plodia interpunctella (Hübner), red flour beetle, Tribolium castaneum (Herbst), and cigarette beetle, Lasioderma serricorne (F.) were the most abundant. Although there were noticeable differences among the different traps and attractants for specific species, all combinations provided similar information on population dynamics. Generally, Dome traps baited with either the oil or the gel, were found to be the most sensitive. The results of the present study demonstrate the importance of long-term trapping protocols, as a keystone in IPM-based control strategies in food processing facilities.

Direct competition and potential displacement involving managed Trogoderma stored product pests.

The establishment of an exotic pest may require displacing local species with a similar niche. The potential of Trogoderma granarium to displace Trogoderma inclusum was explored in a stored product setting. We performed direct competition experiments varying commodity and temperature over different durations. At nine weeks T. inclusum outproduced T. granarium on all commodities at any temperature. However the proportion of T. granarium versus T. inclusum was greater at 32 °C compared to 25 °C. The nine-week production of T. granarium was best on wheat, while rice was optimal for T. inclusum. After 25 weeks, when adults were used at the start of competition, T. inclusum maintained an advantage in the direct competition. If larvae were used to initiate the competition for 25 weeks, the two species coexisted well at 25 °C, but T. granarium nearly excluded T. inclusum at 32 °C. Thus T. inclusum performs better in competition over shorter intervals when resources are plentiful, but T. granarium can be more successful over longer time periods, particularly when late instar larvae are involved. The finding suggests a real threat of introductions of T. granarium larvae to establish populations within grain storage infrastructure where T. inclusum is common.

Development of an array of molecular tools for the identification of khapra beetle (Trogoderma granarium), a destructive beetle of stored food products.

Trogoderma granarium Everts, the khapra beetle, native to the Indian subcontinent, is one of the world's most destructive pests of stored food products. Early detection of this pest facilitates prompt response towards the invasion and prevents the need for costly eradication efforts. Such detection requires proper identification of T. granarium, which morphologically resembles some more frequently encountered, non-quarantine congeners. All life stages of these species are difficult to distinguish using morphological characters. Additionally, biosurveillance trapping can result in the capture of large numbers of specimens awaiting identification. To address these issues, we aim to develop an array of molecular tools to rapidly and accurately identify T. granarium among non-target species. Our crude, cheap DNA extraction method performed well for Trogoderma spp. and is suitable for downstream analyses including sequencing and real-time PCR (qPCR). We developed a simple quick assay usingrestriction fragment length polymorphism to distinguish between T. granarium and the closely related, congeneric T. variabile Ballion and T. inclusum LeConte. Based on newly generated and published mitochondrial sequence data, we developed a new multiplex TaqMan qPCR assay for T. granarium with improved efficiency and sensitivity over existing qPCR assays. These new tools benefit regulatory agencies and the stored food products industry by providing cost- and time-effective solutions to enhance the identification of T. granarium from related species. They can be added to the existing pest detection toolbox. The selection of which method to use would depend on the intended application.

Comparative Population Growth of the Khapra Beetle (Coleoptera: Dermestidae) and the Warehouse Beetle (Coleoptera: Dermestidae) on Wheat and Rice.

We evaluated the relative population growth of two stored-product insect species in the genus Trogoderma, the khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae), and the warehouse beetle, Trogoderma variabile Ballion (Coleoptera: Dermestidae). Ten adults of each species were placed in vials containing wheat or paddy rice. These tests were performed at 27 and 32°C and the number of adults in the vials were counted after 35 and 70 days. For all the time intervals and temperatures of both species on wheat, the resulting larval abundances were similar, with the exception of 27°C at 70 days where more T. variabile larvae developed. At the higher temperature, both species had similar population growth on rice. However, the success was mixed at 27°C with T. granarium having a greater abundance after 35 days, while T. variabile dominated after 70 days. Frass production in both commodities was usually similar for the two species, but greater frass production occurred by T. variabile on wheat after 70 days at 27°C, while T. granarium produced more frass on rice after 35 days at 32°C. Both species nearly always caused equivalent commodity damage. Our research suggests that under ideal conditions these two closely, but very differently treated species in commerce from the genus Trogoderma have comparable population growth, and cause similar damage on wheat and rice.

Identification of Pheromone Components of Plagionotus detritus (Coleoptera: Cerambycidae), and Attraction of Conspecifics, Competitors, and Natural Enemies to the Pheromone Blend.

(1) Background: The principal aim of our work was to identify pheromone components for Plagionotus detritus (L.) (Coleoptera: Cerambycidae), which could be exploited for developing a pheromone-based monitoring system for the complementary purposes of plant protection in areas where it might become a pest, and natural conservation in areas where it is rare or endangered. (2) Methods: Collection and analysis of headspace volatiles were carried out with field-collected beetles. Bioactive volatile compounds identified [(R)-3-hydroxyhexan-2-one and (S)-2-hydroxyoctan-3-one] from extracts of males were purchased [(±)-3-hydroxyhexan-2-one], and synthesized [(S)-2-hydroxyoctan-3-one] and field-tested. Electroantennogram assays showed that antennae of the predatory beetle Clerus mutillarius F. (Coleoptera: Cleridae) also responded to the synthetic compounds. (3) Results: A two-component aggregation-sex pheromone consisting of (R)-3-hydroxyhexan-2-one and (S)-2-hydroxyoctan-3-one was identified for P. detritus. (±)-3-hydroxyhexan-2-one and (S)-2-hydroxyoctan-3-one attracted adults of P. detritus in field bioassays. Adults of the clerid C. mutillarius also were attracted to both compounds. The cerambycid Xylotrechus antilope Schönh was significantly attracted to traps baited with (S)-2-hydroxyoctan-3-one alone or the blend containing this compound. (4) Conclusions: Our data confirmed that 3-hydroxyhexan-2-one and 2-hydroxyoctan-3-one are male-produced pheromone components for P. detritus. These results show that both intraspecific and interspecific communication may play key roles in longhorn beetle life history and ecology, with closely and more distantly related species eavesdropping on each other's signals.

Comparative Capture of Trogoderma granarium (Coleoptera: Dermestidae) and T. variabile in Floor Traps in Single Species Releases With Previously Captured Conspecific or Heterospecific Individuals.

In the present work, a series of tests were performed to examine the effect of previously captured adults in floor traps, on the captures of Τrogoderma granarium Everts and T. variabile Ballion, in single species releases. In a first series of tests, a single trap with kairomone oil and dead adults of single or both species was placed in a plastic container, which was used as the release arena. Subsequently, adults of both species were separately released in the arena, and the adult capture was recorded 24 h later. In a second series of trials, two traps were placed in the same arena, containing different numbers of prior seeded adults, and adult capture was similarly recorded. For T. granarium, in all cases, more adults were found inside the trap than under the trap or on the trap walls. In contrast, for T. variabile, most adults were recorded on the trap walls. In general, T. variabile had a stronger response to the traps than T. granarium. This work illustrates that previous captures of either species do not negatively affect captures of new live adults and may tend to enhance captures in some cases. This has important implications for the use of traps for the biosureveillance of these two important dermestid species.

Sublethal exposure of Trogoderma granarium everts (Coleoptera: Dermestidae) to insecticide-treated netting alters thigmotactic arrestment and olfactory-mediated anemotaxis.

Long-lasting insecticide treated netting (LLIN) has a number of potential uses for the control of insect pests. Using such netting, stored products may be protected from insects including the khapra beetle (Trogoderma granarium Everts, Coleoptera: Dermestidae) a widespread pest of many agricultural commodities. Here we first examined whether brief exposures of larvae to LLIN, for less than 30 min, decreased the chance of eventual adult emergence compared to larvae exposed on untreated netting. Next, we observed the responses of larvae that were either not exposed to any netting, exposed to untreated netting, or exposed to LLIN for 10 min and then placed in a wind tunnel and monitored for movement toward a stimulus. The wind-tunnel assay was performed either with or without a lure containing kairomones and pheromones known to be attractive to larvae of this species. There was little effect of the LLIN on adult emergence of exposed larvae. However, there were interacting effects of untreated netting and LLIN relating to thigmotaxis and anemotaxis. Larvae not exposed to netting showed increased likelihood of walking upwind if the semiochemical lure was provided, as expected. A similar pattern was observed when the untreated netting was used, but the larvae became more likely to remain stationary in the assay after acclimating to the net. When LLIN was used, the larvae became more likely to move and there was a baseline increase in the likelihood of moving upwind. However, upwind walking was no longer related to semiochemical presentation. These observations suggest that particular care should be used in relation to the airflow patterns and semiochemical landscape of the warehouse settings in which LLIN is deployed.

Bioassays and Methodologies for Insecticide Tests with Larvae of Trogoderma granarium (Everts), the Khapra Beetle.

New insecticide treatment options would be beneficial for control programs for Trogoderma granarium Everts, the khapra beetle, in the United States. Two insecticides were evaluated, the Polyzone® formulation of deltamethrin and a formulation of the insect growth regulator methoprene combined with deltamethrin and the synergist piperonyl butoxide. In the test with Polyzone® deltamethrin, concrete arenas were treated with a low and high rate, and held outside, inside a shed, or inside a lab. Compared to storage in the lab, residue degradation increased slightly in the shed, and then further outside, as evidenced by greater larval survival and adult emergence. Across all environmental treatments, the high rate was more effective than the lower rate. For the combination methoprene product, the effect of food contact with treated surfaces was examined. When treating arenas with food and transferring the food to clean dishes, there was no immediate effect on larval survival, but there was a reduction in survival and emergence to the adult stage after one month. For both tests, larvae apparently often went into diapause after they were introduced onto the treatment arenas. Both treatments could be utilized in management programs if T. granarium infestations are detected.

Benzaldehyde: an alfalfa-related compound for the spring attraction of the pest weevil Sitona humeralis (Coleoptera: Curculionidae).

BACKGROUND: Sitona weevils (Coleoptera: Curculionidae) are a species complex comprising pests of many leguminous crops worldwide, causing damage to young plants as adults and to rootlets as larvae, resulting in significant yield losses. Timely detection of migrating adult weevils is needed to determine when deployment of control measures becomes necessary. With the aim of developing plant volatile-based lures for Sitona spp. detection, we investigated the responses of S. humeralis to host plant-related aromatic compounds. RESULTS: In olfactometer studies, both male and female S. humeralis responded positively to the odour of alfalfa flowers, a source of aromatic volatiles. In single sensillum recordings, basiconic sensilla located on the third and fourth terminal segments of the antennal club of both sexes were found to respond to benzaldehyde at doses of 10-5 and 10-4  g, suggesting that the weevil is able to detect this compound at the peripheral sensory level. In field studies, S. humeralis was attracted to benzaldehyde in the spring, but not in the autumn. CONCLUSION: Benzaldehyde, as described in this study, may be a suitable candidate for the development of monitoring tools for S. humeralis. © 2019 Society of Chemical Industry.

Differences in spectral selectivity between stages of visually guided mating approaches in a buprestid beetle.

Spectral mating preferences were examined in male Agrilus angustulus (Buprestidae: Coleoptera), a member of a taxon known for its high species diversity and striking metallic coloration. The spectral emission profile of a typical A. angustulus female displays low chroma, broadly overlapping that of the green oak leaves they feed and rest upon, while also including longer wavelengths. To pinpoint behaviorally significant spectral regions for A. angustulus males during mate selection, we observed their field approaches to females of five Agrilus planipennis color morphs that have greater chroma than the normal conspecific female targets. Agrilus angustulus males would initially fly equally frequently toward any of the three longest wavelength morphs (green, copper and red) whose spectral emission profiles all overlap that of typical A. angustulus females. However, they usually only completed approaches toward the two longest wavelength morphs, but not the green morphs. Thus, spectral preference influenced mate selection by A. angustulus males, and their discrimination of suitable targets became greater as these targets were approached. This increasing spectral discrimination when approaching targets may have evolved to allow female emissions to remain somewhat cryptic, while also being visible to conspecifics as distinct from the background vegetation and heterospecific competitors.

Interaction of Visual and Chemical CUES in Promoting Attraction of Agrilus planipennis.

Female emerald ash borers, Agrilus planipennis (Coleoptera: Buprestidae), emit a macrocyclic lactone, (Z)-3-dodecen-12-olide, that increases field trap captures on large-panel prism traps when co-emitted with the green leaf volatile (Z)-3-hexenol. We assessed attraction to these compounds by using visual decoy-baited branch traps, which attract males by mimicking a living female resting upon a leaf. Pairs of branch traps, with and without visual decoy beetles, were placed on green ash, Fraxinus pennsylvanica, trees, which were assigned different odor treatments: 1) no odor, 2) (Z)-3-hexenol alone, and 3) (Z)-3-hexenol-plus-lactone. Male captures were positively affected by the presence of decoys and the emission of either (Z)-3-hexenol or (Z)-3-hexenol plus lactone. The decoy-baited traps with the combination of (Z)-3-hexenol plus lactone caught more males than any other treatment. Greater male captures were associated with continuing captures later in the season, suggesting that decoy and odor attractants remain attractive throughout the flight period. Female captures were not affected by the visual decoys, but odors did influence captures, with the (Z)-3-hexenol plus lactone treatment catching the greatest number of females. The rare female trap captures were negatively correlated with the more common male captures on the odorless and (Z)-3-hexenol-baited traps, but were not correlated with male captures when the lactone was added. Thus, in the absence of the lactone, the visual signal of other conspecifics can inhibit female attraction. However, the pheromone attracts both sexes independently of the visual signal on the trap.

Bioreplicated visual features of nanofabricated buprestid beetle decoys evoke stereotypical male mating flights.

Recent advances in nanoscale bioreplication processes present the potential for novel basic and applied research into organismal behavioral processes. Insect behavior potentially could be affected by physical features existing at the nanoscale level. We used nano-bioreplicated visual decoys of female emerald ash borer beetles (Agrilus planipennis) to evoke stereotypical mate-finding behavior, whereby males fly to and alight on the decoys as they would on real females. Using an industrially scalable nanomolding process, we replicated and evaluated the importance of two features of the outer cuticular surface of the beetle's wings: structural interference coloration of the elytra by multilayering of the epicuticle and fine-scale surface features consisting of spicules and spines that scatter light into intense strands. Two types of decoys that lacked one or both of these elements were fabricated, one type nano-bioreplicated and the other 3D-printed with no bioreplicated surface nanostructural elements. Both types were colored with green paint. The light-scattering properties of the nano-bioreplicated surfaces were verified by shining a white laser on the decoys in a dark room and projecting the scattering pattern onto a white surface. Regardless of the coloration mechanism, the nano-bioreplicated decoys evoked the complete attraction and landing sequence of Agrilus males. In contrast, males made brief flying approaches toward the decoys without nanostructured features, but diverted away before alighting on them. The nano-bioreplicated decoys were also electroconductive, a feature used on traps such that beetles alighting onto them were stunned, killed, and collected.

Reduction in host-finding behaviour in fungus-infected mosquitoes is correlated with reduction in olfactory receptor neuron responsiveness.

BACKGROUND: Chemical insecticides against mosquitoes are a major component of malaria control worldwide. Fungal entomopathogens formulated as biopesticides and applied as insecticide residual sprays could augment current control strategies and mitigate the evolution of resistance to chemical-based insecticides. METHODS: Anopheles stephensi mosquitoes were exposed to Beauveria bassiana or Metarhizium acridum fungal spores and sub-lethal effects of exposure to fungal infection were studied, especially the potential for reductions in feeding and host location behaviours related to olfaction. Electrophysiological techniques, such as electroantennogram, electropalpogram and single sensillum recording techniques were then employed to investigate how fungal exposure affected the olfactory responses in mosquitoes. RESULTS: Exposure to B. bassiana caused significant mortality and reduced the propensity of mosquitoes to respond and fly to a feeding stimulus. Exposure to M. acridum spores induced a similar decline in feeding propensity, albeit more slowly than B. bassiana exposure. Reduced host-seeking responses following fungal exposure corresponded to reduced olfactory neuron responsiveness in both antennal electroantennogram and maxillary palp electropalpogram recordings. Single cell recordings from neurons on the palps confirmed that fungal-exposed behavioural non-responders exhibited significantly impaired responsiveness of neurons tuned specifically to 1-octen-3-ol and to a lesser degree, to CO2. CONCLUSIONS: Fungal infection reduces the responsiveness of mosquitoes to host odour cues, both behaviourally and neuronally. These pre-lethal effects are likely to synergize with fungal-induced mortality to further reduce the capacity of mosquito populations exposed to fungal biopesticides to transmit malaria.

4-oxo-aldehydes from the dorsal abdominal glands of the bed bug (Hemiptera: Cimicidae).

Analyses of the dorsal abdominal glands of fourth- and fifth-instar nymphs of the bed bud, Cimex lectularius L. (Hemiptera: Cimicidae), indicated the predominant constituents were (E)-2-hexenal and (E)-2-octenal, with lesser amounts of 4-oxo-(E)-2-hexenal and 4-oxo-(E)-2-octenal. The latter two compounds have not been reported previously as occurring in bed bugs. There were no differences in the chemical composition of the dorsal abdominal glands excised from exuviae left behind by either male or female adults, nor from glands excised from fourth-instar exuviae. Because the two oxo-aldehydes made up at least 16% of the gland contents, further study of the functional role of these chemicals seem advisable.

Homology of olfactory receptor neuron response characteristics inferred from hybrids between Asian and European corn borer moths (Lepidoptera: Crambidae).

First generation hybrid males from crosses between the Asian corn borer (ACB), Ostrinia furnacalis, and the "univoltine Z-strain" European corn borer (ECB), Ostrinia nubilalis, were examined with respect to behavioral and physiological responses to ACB and ECB pheromones. The hybrid males often flew to the pheromone of ECB Z-strain, but very rarely to the ACB pheromone. We mapped the tuning profiles of each ORN of the F(1) hybrids with respect to the relevant pheromone components and a common behavioral antagonist by employing differential cross-adaptation and varying doses of the ligands. In the trichoid sensilla of F(1) hybrid males, the three co-compartmentalized ORNs produced spikes that were very difficult to distinguish by size, unlike the parental populations. Comparing the responses to ACB and ECB components at different doses reveals overlapping profiles similar to males of both parental types, but more responsiveness to the ECB pheromone components. We were unable to detect any differences in the ORN tuning profiles when comparing males with different behavioral phenotypes. While the two ECB pheromone races have similar ORN tuning properties that are different from those in ACB, the spike-amplitude patterns of ECB E-strain and ACB have greater homology when compared to ECB Z-strain.

Altered olfactory receptor neuron responsiveness is correlated with a shift in behavioral response in an evolved colony of the cabbage looper moth, Trichoplusia ni.

There is little understanding of how sex pheromone blends might change during speciation events. For the cabbage looper, Trichoplusia ni, there is a mutant laboratory strain that has exhibited characteristics of a shift to a new pheromone blend. Mutant females produce a blend that is significantly different from wild-type females in having a much higher proportion of a minor pheromone component and lower quantity of the major component. Males in this colony have changed over the years to become more broadly tuned and fly upwind equally well to both the wild-type and mutant female pheromone blends. They also exhibit reduced overall sensitivity to pheromone, flying upwind to either blend at a lower success rate than is typical when wild-type males respond to the wild-type blend. Using single-cell recordings, we examined the olfactory receptor neurons (ORNs) of males from evolved and wild-type colonies for evidence of changes in response characteristics that might explain the above-described behavioral evolution. We found that in evolved-colony males the ORNs tuned to the major sex pheromone component exhibited a somewhat lower responsiveness to that compound than the ORNs of wild-type males. In addition, the minor pheromone component, emitted at excessively high rates by mutant females, elicited a drastically reduced ORN responsiveness in evolved-colony males compared to wild-type males. This alteration in ORN responsiveness may be responsible for allowing evolved males to tolerate the excessive amounts of the minor pheromone component in the mutant female blend, which would normally antagonize the upwind flight of unevolved males. Thus, peripheral olfactory alterations have occurred in T. ni males that are correlated with the evolution of the more broadly tuned, but less sensitive, behavioral response profile.

Olfactory neuron responsiveness and pheromone blend preference in hybrids between Ostrinia furnacalis and Ostrinia nubilalis (Lepidoptera: Crambidae).

The olfactory receptor neuron (ORN) and behavioral responses of hybrids between the Asian corn borer (ACB), Ostrinia furnacalis, and the E-strain European corn borer (ECB(E)), Ostrinia nubilalis were examined and compared to the parental populations. In hybrids and both parents, the large-spike-size ORN was capable of responding to all four pheromone components of ACB and ECB, despite differences in which compounds elicited the greatest spike frequency in each population. There was a small-spiking ORN more narrowly tuned to the minor pheromone components in both ACB and ECB(E). In hybrids the homologous small-spiking ORN was tuned primarily to the ECB(E) minor pheromone component, with some responsiveness to the ACB minor component. Both species and all the hybrids had an intermediate spike-size ORN tuned primarily to their common behavioral antagonist. Dominance of responsiveness to the ECB(E) versus the ACB minor pheromone component on the small-spiking ORN may explain the greater tendency of hybrids to fly upwind to the ECB(E) pheromone blend than the ACB blend. This finding points toward a distinct evolutionary role for this ORN in allowing a pheromone shift.

Altered olfactory receptor neuron responsiveness in rare Ostrinia nubilalis males attracted to the O. furnacalis pheromone blend.

Three percent of E-strain Ostrinia nubilalis males fly upwind in response to the Ostrinia furnacalis pheromone blend [a 40:60 ratio of (E)-12-tetradecenyl acetate to (Z)-12-tetradecenyl acetate (E12-14:OAc to Z12-14:OAc)], in addition to their own pheromone blend [a 99:1 ratio of (E)-11-tetradecenyl acetate to (Z)-11-tetradecenyl acetate) (E11-14:OAc to Z11-14:OAc)]. We assessed the olfactory receptor neuron (ORN) responses of these behaviorally "rare" males versus those of normal males. For the three ORNs housed within each sensillum, we tested responsiveness to Z12-14:OAc, E12-14:OAc, Z11-14:OAc, E11-14:OAc, and the behavioral antagonist (Z)-9-tetradecenyl acetate (Z9-14:OAc). Z11-14:OAc, E11-14:OAc, and Z9-14:OAc stimulated ORNs exhibiting distinct small, large, and medium spike sizes, respectively. For rare and normal males, both Z12-14:OAc and E12-14:OAc usually elicited responses from the largest-spiking ORN. In many ORNs of normal males, Z12-14:OAc or E12-14:OAc stimulated the smaller-spiking ORN that is responsive to Z11-14:OAc. In rare males, detectable ORN responses from the smaller-spiking ORN in response to Z12- and E12-14:OAc were virtually non-existent. These differences in ORN tuning in rare males will tend to create an ORN firing ratio between the large- and small-spiking ORNs in response to the O. furnacalis blend that is similar to that elicited by the O. nubilalis blend.