Xiangbo Kong

Antennal morphology and sensilla ultrastructure of Dendroctonus valens LeConte (Coleoptera: Curculionidae, Seolytinae), an invasive forest pest in China

Dendroctonus valens LeConte, an invasive forest pest, is highly dependent on its olfactory system for activities such as host seeking, mating, oviposition and population aggregation. The antennae are the primary olfactory organs in bark beetles. We describe four morphological types of sensilla on the antenna of D. valens: (1) 3 subtypes of sensilla trichodea located at the apex and lateral surface of the club. Sensilla trichodea types 1 and 3 were innervated by 5 and 13 dendrites, respectively. Sensilla trichode type 2 was not found dendrites in a lumen, (2) sensilla chaetica found on the scape and funicle and innervated by 7 dendrites, (3) a pair of sensilla basiconica distributed primarily on the three sensory bands, each innervated by 2 dendrites at the base, and (4) one fluted cone type of grooved peg dispersed throughout the sensory bands. The possible functions of these sensilla are discussed in relation to their morphology and ultrastructure.

Sexual dimorphism in antennal morphology and sensilla ultrastructure of Dendrolimus tabulaeformis Tsai et Liu (Lepidoptera: Lasiocampidae)

Insects rely heavily on olfaction to locate habitat, mates, and oviposition sites, while odorant molecules and the antennal olfactory sensory cells of insects are two indispensable components of olfactory response. Our previous work identified the sex pheromones and volatile compounds derived from host plant of Dendrolimus tabulaeformis Tsai et Liu, a serious economic pest of pines in northern China. However, little is known about the olfactory system of D. tabulaeformis, especially in females. To make a better understanding of the D. tabulaeformis olfactory response, we investigated the structure, innervation, numbers, and distribution of sensilla on the antennae of male and female moth, based on scanning and transmission electron microscopy. The pinniform antennae of this moth bear five types of sensilla: trichoid (TS), basiconica (BS), styloconic (StS), and chaetica (ChS) sensilla, and belt‐type structures (BTSs). The BTSs are hollow and are not chemical sensilla. The ChSs occur on the scape. StS contain dendrite sheaths and four dendrites containing microtubules in their cores. The BS contents are continuous with that in the subsegments. The TSs were sexually dimorphic and could be divided into 12 subtypes based on dendrite number and form. TS1‐4 contained two, three, or four dendrites and were similar in both sexes. TS 5‐8 and TS 9‐12 occurred only on male and female antenna, respectively. We discussed the possible functions of these sensilla. Microsc. Res. Tech., 2013.

Antennal morphology and sensilla ultrastructure of the web-spinning sawfly Acantholyda posticalis Matsumura (Hymenoptera: Pamphiliidae)

Acantholyda posticalis (Hymenoptera: Pamphiliidae) is an important pine pest with a world-wide distribution. To clarify the olfactory receptive mechanism of A. posticalis, scanning electron microscopy and transmission electron microscopy were used to examine the morphology, ultrastructure, and distribution of antennal sensilla of adults from two sites in China. The antennae were filiform, and the flagella comprised 32-35 flagellomeres. Six sensillum types were found. Sensilla chaetica were straight setae with sharply pointed tips and without dendrites in the lumen. Sensilla trichodea were characterized by a parallel-grooved wall and one terminal pore and were innervated by four dendrites at the base. Sensilla basiconica I possessed longitudinally grooved surfaces and multiple terminal pores, with five dendrites in the lumen. Sensilla basiconica II not only had a distinct terminal pore but also had numerous tiny wall pores and many dendritic branches within the sensillum lymph. Sensilla coeloconica had deep longitudinal grooves, one terminal pore and six dendrites, while sensilla campaniformia were thick-walled with a terminal opening and sensory nerve bundles in the lumen. Sensilla chaetica and s. trichodea were most abundant and distributed over the entire antennae, while s. basiconica I and II, s. coeloconica, and s. campaniformia were restricted to the ventral flagellar surfaces. Although the shape and structure of antennae were similar in males and females, females had significantly longer antennae than males, and males had significantly more s. basiconica I than females. We compared the morphology and structure of these sensilla to other Hymenoptera and discussed their possible functions.

Antennal morphology and sensilla ultrastructure of three tomicus species (coleoptera: Curculionidae, scolytinae)

The antennal morphology and sensilla ultrastructure of Tomicus yunnanensis, T. minor, and T. brevipilosus were studied by scanning electron microscopy and transmission electron microscopy. Eight common sensilla types were recorded: (1) sensilla trichodea (S.tr.) types 1 and 2 were located on the club and were innervated by five and eight dendrites, respectively; (2) sensilla chaetica (S.ch.) types 1 and 2 had no dendrites in the sensilla lymph lumen; (3) sensilla basiconica (S.b.), top‐protuberated S.b. and fluted cones (Fl.c.) occurred on the club; and Böhm bristles (B.b.) occurred on the funicle. S.b. were the most abundant and were innervated by 10–14 dendritic branches. Top‐protuberated S.b., a new sensilla type, were innervated by one dendrite. Fl.c. were innervated by five dendrites. Only three sensilla furcatea were visible on the antennae of female T. yunnanensis. The possible functions of these sensilla are discussed in relation to their morphology and ultrastructure. No statistical differences between sexes were found in the size and numbers of each sensilla type. Although the three species had similar antennal morphology and sensilla type, sensilla on sub‐segments 3 and 4 of the antennal club of T. minor were much sparser than those of T. yunnanensis or T. brevipilosus. Concerning the antennae of T. yunnanensis, there were more S.tr. type 2, S.ch. type 2 and S.b. and the size of S.tr. type 1 and S.b. were significantly greater than those of T. minor. Microsc. Res. Tech., 2012.

Molecular characterization and phylogenetic analysis of three odorant binding protein gene transcripts in Dendrolimus species (Lepidoptera: Lasiocampidae).

Pine caterpillar moths, Dendrolimus spp. (Lepidoptera: Lasiocampidae), are serious economic pest of pines. Previously, phylogenetic analyses of Dendrolimus using different methods yielded inconsistent results. The chemosensory systems of insects may play fundamental roles in promoting speciation. Odorant‐binding proteins (OBPs) participate in the first step of odor detection. Studying the evolution of OBPs in closely related species may help us to identify their role in speciation. We identified three OBPs – one pheromone‐binding protein and two general odorant‐binding proteins – from male antennae of four Dendrolimus species, D. superans (Butler), D. punctatus (Walker), D. kikuchii Matsumura, and D. houi Lajonquiere, the olfactory recognition systems of which had not been previously investigated. We analyzed their molecular characteristics and compared their sequences to those of OBPs in D. tabulaeformis Tsai et Liu. Ka/Ks ratio analyses among the five Dendrolimus species indicate that PBP1 genes experienced more evolutionary pressure than the GOBPs. Phylogenetic relationships of PBP1 and GOBP1 both indicated that D. houi was the basal species, then branched D. kikuchii, while D. tabulaeformis, D. punctatus, and D. superans evolved more recently. These relationships are consistent with the changes in sex pheromone components of these five species. Dendrolimus tabulaeformis and D. punctatus are closely related sister species. However, the distances among GOBP2 sequences in the five Dendrolimus were very short, and the relationships of D. houi and D. kikuchii could not be resolved. Integrating our results with those of previous studies, we hypothesized that D. kikuchii, D. punctatus and D. superans evolved from the basal ancestor because of sex pheromone mutations and environmental pressure.

Identification and Behavioral Evaluation of Sex Pheromone Components of the Chinese Pine Caterpillar Moth, Dendrolimus tabulaeformis

Background The Chinese pine caterpillar moth, Dendrolimus tabulaeformis Tsai and Liu (Lepidoptera: Lasiocampidae) is the most important defoliator of coniferous trees in northern China. Outbreaks occur over enormous areas and often lead to the death of forests during 2–3 successive years of defoliation. The sex pheromone of D. tabulaeformis was investigated to define its chemistry and behavioral activity. Methodology/Principal Findings Sex pheromone was collected from calling female D. tabulaeformis by headspace solid phase microextraction (SPME) and by solvent extraction of pheromone glands. Extracts were analyzed by coupled gas chromatography/mass spectrometry (GC-MS) and coupled GC-electroantennographic detection (GC-EAD), using antennae from male moths. Five components from the extracts elicited antennal responses. These compounds were identified by a combination of retention indices, electron impact mass spectral matches, and derivatization as (Z)-5-dodecenyl acetate (Z5-12:OAc), (Z)-5-dodecenyl alcohol (Z5-12:OH), (5Z,7E)-5,7-dodecadien-1-yl acetate (Z5,E7-12:OAc), (5Z,7E)-5,7-dodecadien-1-yl propionate (Z5,E7-12:OPr), and (5Z,7E)-5,7-dodecadien-1-ol (Z5,E7-12:OH). Behavioral assays showed that male D. tabulaeformis strongly discriminated against incomplete and aberrant blend ratios. The correct ratio of Z5,E7-12:OAc, Z5,E7-12:OH, and Z5,E7-12:OPr was essential for optimal upwind flight and source contact. The two monoenes, Z5-12:OAc and Z5-12:OH, alone or binary mixtures, had no effect on behavioral responses when added to the optimal three-component blend. Conclusions/Significance The fact that deviations from the optimal ratio of 100∶100∶4.5 of Z5,E7-12:OAc, Z5,EZ7-12:OH, and Z5,E7-12:OPr resulted in marked decreases in male responses suggests that biosynthesis of the pheromone components is precisely controlled. The optimal blend of the sex pheromone components of D. tabulaeformis worked out in this study should find immediate use in monitoring this pest in Chinese forests.

External Morphology of Trichogramma dendrolimi Matsumura (Hymenoptera: Trichogrammatidae) Organ and Ultrastructure of the Sensilla

In this article, we described the ultrastructure of the sensilla on the antenna, eyes, mouthparts, wings, legs, and external genitalia of female and male Trichogramma dendrolimi using scanning electron microscopy (SEM). The antenna possessed the most sensilla types. We found 13 types of sensilla on female antenna, which were trichoid sensilla (TS) type 1‐4, chaetica sensilla (ChS) type 1‐2, campaniform sensilla (CaS), falcate sensilla, placoid sensilla (PS) type 1‐2, basiconic capitate peg sensilla (BCPS) type 1, coeloconic sensilla (CoS), and styloconic sensilla. Ten types of sensilla were found on the male antenna, some were the same as that on female T. dendrolimi antenna, such as TS types 1 and 3, CaS, PS type 1, BCPS type 1, and CoS, but TS types 5 and 6, ChS type 3, and BCPS 2 were specific to male T. dendrolimi antenna. The leg possesses eight types of sensilla and a kind of tympana structure. Four types of TSs were found on the wings. On the mouthparts, sensilla on the maxillary and labial palps were unique, including two TSs and one ChS. The ovipositor possesses three types of sensilla, and the copulatory organ possesses two types. The eyes had only one kind of TS. Furthermore, external morphology of antenna and external genitalia revealed distinct sexual dimorphisms. According to their morphology, the possible functions of these sensilla were discussed. These results may further our understanding of the sensory mechanisms of T. dendrolimi in response to infochemicals within the environment. Microsc. Res. Tech., 2012.

Identification of Components of the Female Sex Pheromone of the Simao Pine Caterpillar Moth, Dendrolimus kikuchii Matsumura

The pine caterpillar moth, Dendrolimus kikuchii Matsumura (Lepidoptera: Lasiocampidae), is a pest of economic importance on pine in southwest China. Three active compounds were detected during analyses of solvent extracts and effluvia sampled by solid phase microextraction (SPME) from virgin female D. kikuchii using gas chromatography (GC) coupled with electroantennographic (EAG) recording with antennae from a male moth. The compounds were identified as (5Z,7E)-5,7-dodecadien-1-yl acetate (Z5,E7-12:OAc), (5Z,7E)-5,7-dodecadien-1-ol (Z5,E7-12:OH), and (5Z)-5-dodecenyl acetate (Z5-12:OAc) by comparison of their GC retention indices, mass spectra, and EAG activities with those of synthetic standards. Microchemical reactions of gland extracts provided further information confirming the identifications of the three components. Solvent extractions and SPME samples of pheromone effluvia from virgin calling females provided 100:18:0.6 and 100:7:1 ratios of Z5,E7-12:OAc:Z5,E7-12:OH:Z5-12:OAc, respectively. Field behavioral assays showed that Z5,E7-12:OAc and Z5,E7-12:OH were essential for attraction of male D. kikuchii moths. However, the most attractive blend contained these three components in a 100:20:25 ratio in a gray rubber septa. Our results demonstrated that the blend of Z5,E7-12:OAc, Z5,E7-12:OH, and Z5-12:OAc comprise the sex pheromone of D. kikuchii. The optimized three-component lure blend is recommended for monitoring D. kikuchii infestations.

Sensory and immune genes identification and analysis in a widely used parasitoid wasp Trichogramma dendrolimi (Hymenoptera: Trichogrammatidae)

Trichogramma dendrolimi Matsumura (Hymenoptera: Trichogrammatidae) is one of the preponderant egg parasitoids of Dendrolimus spp., which are important defoliators of coniferous forests. This parasitoid wasp has been widely released to control pine caterpillar and other lepidopteran pests, but its control efficiency needs to be improved. Sensory systems are crucial for T. dendrolimi to locate hosts, and immunity is probably involved after egg deposition in the host cavity; however, few reports have focused on the molecular mechanism of olfactory detection and survival of T. dendrolimi. It is necessary to identify these genes before further functional research is conducted. In this study, we assembled and analyzed the transcriptome of T. dendrolimi using next‐generation sequencing technology. The sequencing and assembly resulted in 38 565 contigs with N50 of 3422 bp. Sequence comparison indicate that T. dendrolimi sequences are very similar to those of another parasitoid Nasonia vitripennis. Then the olfactory, vision, and immune‐related gene families were identified, and phylogenetic analyses were performed with these genes from T. dendrolimi and other model insect species. Furthermore, phylogenetic tree with odorant binding proteins of T. dendrolimi and their host Dendrolimus was constructed to determine whether convergent evolution exists. These genes can be valid targets for further gene function research. The present study may help us to understand host location and survival mechanisms of T. dendrolimi and to use them more efficiently for pest control in the future.

Population divergence of aggregation pheromone responses in Ips subelongatus in northeastern China

The Asian larch bark beetle, Ips subelongatus, is considered to be the major pest of larch within its natural range. We investigated the electrophysiological and behavioral characteristics as well as mitochondrial DNA cytochrome oxidase subunit I sequences of I. subelongatus from 13 geographic populations throughout northeastern China in order to explore population divergence of aggregation pheromone responses and the extent of potential genetic divergence. Electrophysiological analyses showed that antennae of I. subelongatus from all the six tested populations responded strongly to (S)‐(−)‐ipsenol (100% detection; 0.35–0.73 mV) in gas chromatography (GC)–electroantennographic detection (EAD) analyses, while its antipode, (R)‐(+)‐ipsenol was antennally inactive. I. subelongatus populations varied in their responses to (R)‐(−)‐ and (S)‐(+)‐ipsdienol in GC‐EAD analyses. Behavioral bioassays demonstrated that (S)‐(−)‐ipsenol alone was significantly attractive at all the tested sites, supporting its status as a key pheromone component of I. subelongatus, whereas (S)‐(+)‐ipsdienol was inactive alone. Adding (S)‐(+)‐ipsdienol to (S)‐(−)‐ipsenol did not have any effect on the trap catches from some populations in Inner Mongolia. However, (S)‐(+)‐ipsdienol showed a strong synergistic effect on (S)‐(−)‐ipsenol from several populations in Jilin and Liaoning Provinces, and a weak synergistic effect from some transition populations in Heilongjiang Province. Furthermore, 27 mitochondrial haplotypes were found among the 13 populations (intraspecific nucleotide divergence, 0.1%–1.1%). Analyses of molecular variance and haplotype networks indicated that different geographic populations have developed some genetic variation but did not form completely independent groups. From an applied point of view, a universal synthetic binary blend of racemic ipsenol and (S)‐(+)‐ipsdienol might have a potential for monitoring or even mass‐trapping of I. subelongatus across northeastern China, even though some populations only use (S)‐(−)‐ipsenol alone as their active pheromone component.