Seasonal synchrony between pheromone trap catches of the bean bug, <Emphasis Type="Italic">Riptortus pedestris</Emphasis> (Heteroptera: Alydidae) and the timing of invasion of soybean fields

Seasonal catches of the bean bug, Riptortus pedestris (Fabricius), captured in traps containing the synthetic pheromone, were investigated under different field conditions from 2005 to 2007. In soybean fields, the number of bugs attracted to the pheromone traps increased after flowering and peaked 9–13 days after flowering. After these attraction peaks, the populations of adult bugs and nymphs increased in soybean fields. In traps located in grassland, however, only small numbers of the bugs were caught during the soybean flowering stages (from mid August to early September). The sex ratio of adults caught in the pheromone traps differed among soybean growth stages. Before flowering, more males were caught than females. After flowering, trapped females increased in number and the proportion of females exceeded 0.5 throughout the flowering periods. These results suggest that attraction to the pheromone may be affected by host plant phenology, and that females, in particular, respond strongly to the pheromone during flowering of the host plant soybean.     

Sex pheromones in the cereal aphid parasitoidsPraon volucre andAphidius rhopalosiphi

Laboratory and field experiments provided evidence for the release of sex pheromones by virgin femalePraon volucre Haliday andAphidius rhopalosiphi De Stefani-Perez (Hymenoptera: Braconidae, Aphidiinae). In Petri dish biosassays, rubber or vermiculite models treated with crude virgin female extracts were frequently approached by males and elicited rapid wing-fanning behaviour and copulation attempts. Delta-shaped water traps containing live virgin females caught large numbers of conspecific males when placed in winter wheat crops. Trapping slightly below crop height resulted in higher catches than trapping above the crop canopy.     

The responses ofPraon spp. parasitoids to aphid sex pheromone components in the field

In autumn 1991, aphid parasitoids of the genusPraon (Hymenoptera; Braconidae) were caught in water traps with lures containing synthetic aphid sex pheromone components at three sites in England and one in Germany. At two of the English sites and at the German site, the traps were placed in winter cereal fields whilst the third English site was in woodland. Three species were caught,P. volucre, P. dorsale andP. abjectum. Those caught in cereal fields were almost entirelyP. volucre, whilstP. dorsale dominated at the woodland site. Of the known aphid sex pheromone components, the most effective lure was the (+)-(4aS, 7S, 7aR)-nepetalactone. Nepetalactone traps placed at the woodland site in spring and summer caught fewPraon females, and attraction may be confined to the autumn, when sexual female aphids are present in the field. Male parasitoids did not respond to the aphid pheromones at any time, although they were caught in suction traps operated at the woodland site during the autumn. At the cereal sites height had a significant influence on the efficiency of the pheromone traps, those placed just above the crop canopy being most effective. There was no evidence that any other genus of parasitoid responded to aphid sex pheromones at these sites.     

Interspecific larval competition between two egg parasitoids in refrigerated host eggs of Riptortus pedestris (Hemiptera: Alydidae)

In a previous study, we found that soybean fields could be supplemented with refrigerated eggs of Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) to enhance parasitism. As a part of a study to evaluate the effect of host egg refrigeration on parasitism, host acceptance behavior and interspecific larval competition between Gryon japonicum (Ashmead) (Hymenoptera: Scelionidae) and Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) were studied in multiparasitized unrefrigerated and refrigerated eggs. O. nezarae showed complete host acceptance behavior when offered refrigerated host eggs that were preparasitized by G. japonicum. Adult emergence rate of O. nezarae was 43 and 74% when the interval between the first and second oviposition was 0 and 4 days, respectively, and was not different between refrigerated and unrefrigerated eggs. Refrigeration did not change host acceptance behavior of G. japonicum, but adult emergence declined from 80% in unrefrigerated eggs to 37% in refrigerated eggs that were pre-parasitized by O. nezarae on the same day. No negative effects of refrigeration on sex ratio, adult longevity, and adult size of the both parasitoids were found. Generally host egg refrigeration did not negatively affect host acceptance behavior of the both parasitoids on preparasitized eggs or larval competition between the two parasitoids in multiparasitized host eggs with exceptions in the development time and emergence rate of G. japonicum. Therefore, host egg refrigeration may not interrupt interactions between the parasitoid populations in the field.     

HOST-INDUCED ASSORTATIVE MATING IN HOST RACES OF THE LARCH BUDMOTH

Abstract The likelihood of sympatric speciation is enhanced when assortative mating is a by‐product of adaptation to different habitats. Pleiotropy of this kind is recognized as important in parasites that use their hosts as a long‐range cue for finding mates, but is generally assumed to have limited applicability for most other organisms. In the larch budmoth, Zeiraphera diniana (Lepidoptera: Tortricidae), sympatric host races feed on larch or pine. Zeiraphera diniana females attract males (call) by releasing host‐independent long‐range pheromones. Pheromone composition differs strongly between host races, but we show in an experimental field study that cross‐attraction can occur at a rate of 0.03–0.38. Cross‐attraction to larch females increases when they call from neighborhoods (8‐m radius) rich in pine or from pine trees. Cross‐attraction to pine females similarly increases when calling from neighborhoods rich in larch, but there is no significant effect of calling substrate. Males, as well as females, of this species preferentially alight on their own host, and in neighborhoods where their own host is common. This effect of tree species and host neighborhood on assortative mating is therefore due, at least in part, to the numbers of males of each host race present within approximately 200 m² surrounding the female. This proximity effect is enhanced by the clumped distributions of the hosts themselves. Host chemistry might also affect pheromone production and/or response directly, but we have evidence neither for nor against this. This work provides empirical evidence that host adaptation has a pleiotropic effect on assortative mating in a species with host‐independent long‐range mating signals. Sympatric speciation via pleiotropy between ecological traits and assortative mating may thus be more common than generally supposed: Clumped resource distributions and habitat choice by adults are widespread.     

Sex pheromone and visual trap interactions in mate location strategies and aggregation by host-alternating aphids in the field

Abstract. Field observations were made on the responses of males and gynoparae of three host-alternating aphid species, the blackberry-cereal aphid, Sitobion fragariae (Walker), the bird cherry-oat aphid, Rhopalosiphum padi (L.) and the damson-hop aphid, Phorodon humuli (Schrank) to species-specific sex pheromones released from transparent and coloured water traps.Pheromone traps caught significantly more males than did control traps without pheromone, whereas transparent, light green, yellow and orange traps caught most insects.Measurements of the distance over which sex pheromones function indicated that male P.humuli detect the pheromone 2–6 m from the source and can fly upwind to a source in wind speeds of 0.7 m s^-1.In all three species significantly more gynoparae were caught in pheromone traps than in control traps, suggesting that pheromone released by adult sexual females may assist late-flying gynoparae to locate a suitable host plant on which to deposit their progeny.The response is relatively stronger for males than gynoparae, but the pheromones appear to act as both sex and aggregation pheromones.     

Vertical distribution of codling moth adults in pheromone-treated and untreated plots

The vertical distribution of codling moth,Cydia pomonella (L.) within pheromone-treated and untreated apple and pear orchard canopies was determined using tethered virgin females, unbaited sticky traps, and blacklight observation of released moths. Mating of virgin females tethered at various heights in untreated orchard canopies increased with placement height from 1–4 m. Application of pheromone dispensers for mating disruption at 2 and 4 m above the ground greatly decreased mating. Greatest capture of males and females on unbaited sticky traps occurred at mid- and upper-canopy heights. Total capture of males and females in pheromone-treated plots was not statistically different than in untreated plots. The percentage of mated females captured on sticky traps did not vary with trap height or pheromone treatment. Released moths marked with flourescent powder and observed at dark with a blacklight indicated that moths are primarily distributed high in the canopy. However, males shifted to a position lower in the canopy when pheromone dispensers were placed 2.1 m above the ground. Results suggest that pheromone dispensers be placed in the upper canopy for optimal disruption of codling moth mating.     

Winter survival and oviposition before and after overwintering of a parasitoid wasp, Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae)

Winter survival and oviposition before and after overwintering in Ooencyrtus nezarae, an egg parasitoid of phytophagous heteropterans, were examined in Osaka, Japan. Eggs of Riptortus clavatus parasitized by O. nezarae were kept under natural photoperiod and temperature. When honey was supplied, some female adults emerging from early September to late November overwintered. The percentage of overwintering individuals increased as the date of adult emergence advanced. Most female adults supplied with honey and hosts oviposited soon after emergence, then stopped laying eggs. Female adults emerging in mid‐October and early November laid eggs and then overwintered. The induction of diapause in the field seems to vary greatly depending on host availability. Without honey, the survival time of female adults was very short, whether host eggs were supplied or not. After overwintering, most females began to lay eggs in early May if host eggs were supplied, and they produced both male and female progeny. In the study area, a legume field in Osaka, parasitization by O. nezarae was observed from early July to November.     

Orientation of males of sorghum midge,Contarinia sorghicola to sex pheromones from virgin females in the field

The orientation of males of the sorghum midge,Contarinia sorghicola Coq. (Diptera: Cecidomyiidae) towards virgin female baited sticky traps was studied in the field. Male response increased linearly with an increase in the number of virgin females in the sticky traps. Five females per vial were optimum for monitoring midge populations in the field. Numbers of males trapped were significantly greater in traps placed at 0.5 and 1.5 m above ground level compared with those placed at 2.5 m. Peak trap catches occurred at 0900 h. The number of males trapped decreased significantly after 1400 h; male catches continued till sunset. Trap catches followed the same pattern as the number of ovipositing females on sorghum panicles at the half-anthesis stage. Midge activity decreased with an increase in temperature and a decrease in relative humidity. Peak midge density was observed during the second fortnight of October in the rainy season and during February-March in the post-rainy season. Sex pheromones can be used to monitor midge population dynamics for integrated pest management and to screen for host plant resistance to this insect.     

Effect of soybean canopy closure on landing rates of aphids with implications for restricting spread of soybean mosaic virus

Alate Aphis citricola and Myzocallis punctatus were caught more abundantly on horizontal ermine-lime canopy-level sticky traps in a closed soybean canopy than on similar traps in an open canopy. This is the first reported case in which more alate aphids were collected on traps in fields with relatively more ground cover. Capitophorus elaeagni were caught more abundantly on traps in relatively more open canopy, and Lipaphis erysimi, Rhopalosiphum maidis and Schizaphis graminum were collected in statistically similar numbers in open and closed canopies. Our trapping technique was designed in an attempt to collect only those aphids which would otherwise have landed on the soybean canopy. Landing rates differed among species; therefore, the efficacy of using ground cover manipulation to reduce spread of soybean mosaic virus would depend upon seasonal occurrence of the important local vector species.     

Spatio‐temporal distribution of Ceratitis capitata population in a heterogeneous landscape in Central Italy

The spatio‐temporal dynamics of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), was investigated to evaluate the effect of the landscape elements and host plants on pest distribution, in an agricultural landscape of 500 ha located in Central Italy. Two farms (farm 1 and farm 2) are located in the experimental area, composing mixed fruit orchards and surrounded by hedgerows, small woodlots, private gardens and cereal fields. Ceratitis capitata population fluctuation was monitored, from 2006 to 2008, using traps baited with trimedlure. Geostatistical methods such as Inverse distance squared weighted were used to obtain distributional maps of adults, mainly males. Results showed that the adult Mediterranean fruit flies were primarily distributed inside farm 1, with the maximum density found in the months of September and October. Away from the principal host plants, particularly in cereal fields, the number of trapped individuals was always low or zero. In both farms, flies were caught sequentially in traps located on host plants (i.e. peach, apple, pear, oriental persimmon and prickly pear) at varying times of maturation, especially when fruits remained on the trees. Distributional maps provided evidence that allowed to identify habitats in which the fly developed early in the season (mixed peach orchards) and afterwards during the periodic flights.     

The Flight Heights of Chalcid Wasps (Hymenoptera,Chalcidoidea) in a Lowland Bornean Rain Forest: Fig Wasps are the High Fliers1

Tropical rain forests are characterized by their rich plant diversity and highly diverse insect faunas containing mainly rare species. Phytophagous and parasitoid insects utilizing such fragmented resources often must travel considerable distances to find suitable hosts. For small, weak‐flying insects, entry into the fast‐flowing air above the canopy can provide one way by which long‐distance dispersal is achieved. Using sticky traps placed at different heights in a lowland rain forest of Borneo, we compared the diurnal and nocturnal flight heights of chalcids, a group of mainly very small parasitoids and phytophages, to determine if the air above the canopy was used for dispersal. Most families were represented throughout the range of trap heights, including those above the general canopy. A higher proportion of individuals were trapped above the canopy at night than during the day. Fig wasps were exceptional in that they were trapped almost entirely above the canopy. They included species associated with host trees that do not fruit in the canopy, suggesting that these short‐lived, slow‐flying insects actively fly up above the canopy and then use the wind to passively carry them the long distances needed to reach their highly localized and ephemeral hosts. Once the fig wasps detect the species‐specific volatiles released by their host figs, they then may fly down into the canopy, where the lower wind speeds would allow them to fly actively upwind to their hosts.     

Ecotoxicological effect of insecticides on Ooencyrtus nezarae (Hymenoptera: Encyrtidae) reared from refrigerated and unrefrigerated Riptortus pedestris (Hemiptera: Alydidae) host

Due to increased field occurrence of Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) on various crops including soybean, persimmon and apple in recent years in Korea, demand for insecticide applications to control the stink bug has increased. Acute toxicity of eight pesticides on Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae), a major egg parasitoid of R. pedestris, was compared in the laboratory. Fenitrothion, spinosad, cyfluthrin, etofenprox and carbosulfan caused 100% mortality of O. nezarae within 24 hours by topical application or exposure to residue. Fenitrothion was also highly toxic to the parasitoid when ingested orally. In a previous study, release of refrigerated inviable eggs of R. pedestris was found to increase field parasitism; therefore, we evaluated the sublethal effect of fenitrothion when O. nezarae parasitised refrigerated or unrefrigerated host eggs. Although parasitism rates on both kinds of eggs significantly decreased when O. nezarae were provided with host eggs sprayed with fenitrothion, no difference in parasitism rate, adult emergence, sex ratio, development time and longevity of O. nezarae was found between the refrigerated or unrefrigerated host eggs when the insecticide was treated either before or after oviposition. There was no significant sublethal effect when parasitised host eggs were treated with the insecticide. From these results, all the insecticides tested showed high, acute toxicity against O. nezarae with relatively lower sublethal effects. Refrigeration of host eggs did not affect the susceptibility of O. nezarae to insecticides.     

昆虫寄主标记信息素

综述了昆虫寄主标记信息素的研究进展。昆虫寄主标记信息素是指由昆虫产生的用来标记寄主上有同种个体存在的化学物质。昆虫寄主标记信息素的主要生态学功能是调节昆虫的产卵行为,通过阻止自身或同种其它个体对已标记寄主的产卵选择,或减少产卵量来减少后代之间对寄主资源的竞争。寄主标记信息素也会给释放着带来不利的影响,如信息盗用和盗寄生现象等。昆虫寄主标记信息素也调节昆虫近缘种之间对共同寄主资源的竞争。近缘种昆虫对相互寄主标记信息素识别能力的差异反映了不同昆虫对同一寄主资源竞争能力的强弱。寄主标记信息素产生和贮存的部位一般与外分泌腺、消化系统或生殖系统相联系,杜氏腺、毒腺、前胸腺、腹腺、下唇腺、后产卵管、卵巢、中肠和后肠等是产生或贮存寄主标记信息素的常见部位。产生的寄主标记信息素一般在成虫产卵时由产卵器、口器或排泄口释放到寄主体内或体表。卵寄生蜂的寄主标记信息素一般标记在寄主的体表,雌成蜂用触角检测;其它寄生蜂的寄主标记信息素常产在寄主体内,用产卵器检测;植食性昆虫的寄主标记信息素只产在寄主表面,用触角或产卵器检测。昆虫的产卵器、口器、触角或跗节上着生有感受寄主标记信息素的化感器,可以检测到标记在寄主体内或体表的寄主标记信息素。昆虫寄主标记信息素的完全定性涉及活性化合物的分离、鉴定、合成以及行为测定等,已有几种昆虫的寄主标记信息素成分得到了分离鉴定。     

THE PREFERENCE AND DENSITY RESPONSES OF EGG PARASITOID,OOENCYRTUS NEZARAE ISHO,TO THE EGGS OF SOYBEAN STICK BUGS,RIPTORTUS CLAVATUS THUNBERG AND PIEZODORUS HYBNERI GMELIN*

Abstract The preference and density response test9 of egg parasitoid, Ooencyrtus nezarae Ishii, to the eggs of soybean stick bugs, Riptortus clavatus Thunberg and Piezodorus hybneri Gmelin, were carried out in this study. In the free choice test, O. nezarae emerged from both eggs of stick bug prefer R. clavatus eggs only in the various ratios of host egg densities. In non‐choice test, O. nezarae emerged from P. hybneri eggs parasitize both R. clavatus and P. hybneri eggs, showing a high parasitism on host eggs. However, O. nezarae reared on R. clavatus eggs had a significantly lower parasitism on the eggs of P. hybneri. Olfactometer test showed that the odor emitted from R. clavatus eggs had a great influence on the host searching and parasitizing behavior of O. nezarae. The number of R. clavatus and P. hybneri eggs parasitized by O. nezarae gradually increased with the increase of host egg densities. However, the parasitism of O. nezarae to R. clavatus eggs decreased with the increase of host density. The parasitism of O. nezarae are significantly lower (P < 0.05) on host egg P. hybneri under the laboratory condition, especially for O. nezarae emerged from R. clavatus eggs. This research results implied that in the soybean field, there were some optimal or spatial barriers for O. nezarae to find R. clavatus eggs efficiently.     

Sampling method affects estimates of population density and reproductive maturity of summer‐form pistachio psyllids

Abstract

In this study, the effects of using three different sampling methods (yellow sticky traps, beating tray, organdy bags) on estimating the distribution through the canopy of the summer‐form adults of the pistachio psyllid (Agonoscena targionii (Licht.)) was investigated throughout the vegetative period. The traps or bags were hung at two heights in the tree canopy, 3.5 m above ground and 2 m above ground. Psyllids were counted weekly, and their sex determined. Adult abundance varied during the study, but all three sampling methods indicated that densities were higher in the upper canopy than the lower canopy. The percentage of females having mature eggs was lowest in late May, and highest in June and September. Sex ratios were highly variable among sampling dates and among sampling methods, at both canopy heights. Sex ratios in bags tended to be more female‐biased in the lower canopy than in the upper canopy. Sticky trap counts were significantly male biased, more so in the upper canopy than in the lower canopy. Mean sex ratios differed significantly between bag and sticky trap samples at both heights, but did not differ significantly between tray and bag samples at either height. In addition, for a given tray or bag count, sticky trap catch of males was larger than catch of females, and was larger in the upper canopy than in the lower canopy. Bag counts (psyllids per leaflet) strongly increased with tray count.

Of the three sampling methods described here, the bag samples provided direct estimates of psyllid numbers per leaflet, but this method is extremely time consuming. Bag counts (psyllids per leaflet) increased with tray count, suggesting that beat trays can be used to estimate absolute densities.     

Trapping oestrid parasites of reindeer: the relative age, fat body content and gonotrophic conditions of Cephenemyia trompeand Hypoderma tarandifemales caught in baited traps

Abstract. Dissection of flies caught in northern Norway revealed that only mated, gravid females of H.tarandi (L.) and larviparous C.trompe (Modeer) were caught in host-mimicking C0₂-baited traps. Trapped females had the same gonotrophic and fat body (FB) conditions as females caught on and around reindeer. Most trapped females of both species were of middle to old age, having only one-half to no FB reserves left and only a few to moderate numbers of eggs or larvae remaining. Most young females trapped also had previously oviposited or larviposited at least once, and some newly eclosed, mated females were present throughout the fly season. Based on the known location of reindeer herds, it was evident that trapped flies that had recently oviposited or larviposited had dispersed into the trapping area from 25–100 km away. Declining FB reserves sustained wild-caught C.trompe females (and in utero larvae) in the laboratory for 14 days and H.tarandi females for 18 days. Reserve FB also was depleted during long flights. Females of both species that flew for the longest times (5.1–11.7 h) on a laboratory flight mill had low FB reserves, but nearly maximum numbers of eggs or larvae. Conversely, most females that flew for less than 5 h on the flight mill had little or no FB remaining, and few eggs or larvae. The large FB reserves accumulated as larvae feed in the vertebrate host enable the non-feeding adults to survive and infect their hosts even after prolonged periods of flight-inhibiting climatic conditions.     

Determinants of egg load in the soybean aphid parasitoid Binodoxys communis

We used a series of laboratory studies to investigate factors contributing to variability in egg load of the parasitoid Binodoxys communis (Gahan) (Hymenoptera: Braconidae), a biological control agent of the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae). The change in egg load in newly emerged females over time was determined in response to three treatments: post‐eclosion temperature, sugar meals, and host density. Binodoxys communis females emerge with an average egg load of approximately 40 mature eggs that increases to approximately 200 eggs within 24 h of emergence. The egg maturation rate over this time period is higher when females are held at 26 °C than at 18 °C. And although the egg load of sugar‐fed females was slightly higher than that of starved females, this difference was not statistically significant. Binodoxys communis females that were held with 150 hosts for 8 h laid more eggs than those that were held with 30 hosts, and they also matured more eggs over the subsequent 16 h than those held with 30 hosts or no hosts at all. However, we detected no difference in the egg maturation pattern between B. communis females held with the low host density and that of control females held with no hosts at all. Thus, we conclude that enhanced egg maturation in the higher host‐density treatment is more likely explained by a rapid replenishing of partially depleted ovaries than a host‐induced stimulus of egg maturation per se. Taken together, these results suggest a strategy of maintaining a high egg load and thus avoiding or mitigating the negative effects of egg limitation.     

Vertical Concentrations of Fungal Spores above Wheat Fields

Kramer-Collins volumetric spore samplers were used to measure concentrations of Puccinia graminis, P. recondita, Erysiphe graminis, Cladosporium, and Alternaria spores and fungal hyphal fragments within the canopy and at 1, 3, 6 and 14 m above ground level over wheat fields near Manhattan, Kansas, USA. The largest numbers of spores of each of the named fungi and hyphal fragments were trapped during hours when free moisture was not present on host leaf surfaces. As wind velocity increased, the number of spores and hyphal fragments trapped at all heights increased. Airspora trapped at the various sampling heights under all combinations of biometeorological conditions were calculated as ratios. Location and severity of infection or frequency of occurrence of the parent fungi greatly affected the percentage of propagules released in the canopy and escaped into the atmosphere. Less than 40% of P. recondita urediniospores released from tillering plants in the fall and trapped at 20–25 cm were trapped at 1 m, while only 6% of those trapped at 10 cm were trapped at 1 m. Ratios for the average number of spores trapped at 3 m: 1 m during the entire sampling period were similar for P. recondita (0.54), Alternaria (0.57), and E. graminis (0.48). However, the higher ratios that occurred with spores of P. graminis (0.72) and Cladosporium (0.76), and hyphal fragments (0.77) indicate considerable mixing of locally released airspora with airspora from exogenous sources.     

Primary attraction and kairomonal host discrimination in three species of Dendroctonus (Coleoptera: Scolytidae)

Abstract 1 Synthetic blends of bole and foliage volatiles of four sympatric species of conifers were released from pheromone‐baited multiple‐funnel traps to determine if three species of tree‐killing bark beetles (Coleoptera: Scolytidae): (i) exhibited primary attraction to volatiles of their hosts and (ii) discriminated among volatiles of four sympatric species of host and nonhost conifers. 2 Bole and foliage volatiles from Douglas‐fir, Pseudotsuga menziesii (Mirb.) Franco, increased the attraction of coastal and interior Douglas‐fir beetles, Dendroctonus pseudotsugae Hopkins, to pheromone‐baited traps. Primary attraction to bole volatiles was observed in interior D. pseudotsugae. Beetles were significantly less attracted to the pheromone bait when it was combined with volatiles of lodgepole pine, Pinus contorta var. latifolia Engelm. or interior fir, Abies lasiocarpa × bifolia. 3 The monoterpene myrcene synergized attraction of mountain pine beetles, Dendroctonus ponderosae Hopkins, to their aggregation pheromones, but there was no evidence of primary attraction to host volatiles or discrimination among volatiles from the four conifers. 4 There was significant primary attraction of the spruce beetle, Dendroctonus rufipennis Kirby, to bole and foliage volatiles of interior spruce, Picea engelmannii × glauca, but beetles did not discriminate among volatiles of four sympatric conifers when they were combined with pheromone baits. 5 Our results indicate that host volatiles act as kairomones to aid pioneer Douglas‐fir beetles and spruce beetles in host location by primary attraction, and that their role as synergists to aggregation pheromones is significant. For the mountain pine beetle, we conclude that random landing and close range acceptance or rejection of potential hosts would occur in the absence of aggregation pheromones emanating from a tree under attack.