Host Selection Mechanism Of Chlorophorus Caragana

In recent year, Chlorophorus caragana Xie & Wang was found in Ningxia province, which was a kind of important boring species of Caragana. In order to elucidate the host selection mechanism of C. caragana, plant size, volatile components, physical structure characteristics, non-volatile secondary metabolites, nutrient substance of host and non-host tree of C. caragana were compared. Electrophysiological and behavioral responses of C. caragana to five species of Caragana plant volatiles were studied in the laboratory bioassays. The lures derived from different varieties were also evaluated in the field. In addition, adults oviposition selection and larvae artificial feeding experiment were also carried out in the labortory.1. The host plant range of C. caragana, host damage level were evaluated at first time. C. intermedia was mostly damaged, accompanied by C. microphylla. No damage was found as to C. korshinskii, C. brachypoda and C. ordosica. The ground diameter of damaged C. intermedia was about 1.25-2.00 cm and the ground diameter of damaged C. microphylla was about 0.75-1.50 cm. We found 1.50 cm should be a threshold value for ground diameter of damaged plant species. The ground diameter of C. brachypoda and C. ordosica (0.50-0.75cm) were smaller, both of which grow up slowly. The average ground diameter of 10-year-old C. brachypoda and C. ordosica were about 1.04±0.04cm. On the contrary, the ground diameter of C. korshinskii was about 1.90-3.55cm, which grew up quickly. No significant correlation was found between C. caragana damage level and plant height.2. The effect of voaltiles of five Caragana species on C. caragana host orientation selection was carried out in the labortory. Significent difference of volatile substances of five Caragana species was found. C. microphylla, C. intermedia and C. korshinskii were attractive to C. caragana, and they consist of similar volatiles components, including terpenoid compounds ((Z)-β-ocimene、1,3-pentadiene、β-elemene、limonene and β-pinene), ketone compounds (isophorone) and ester compound (cis-3-hexenyl acetate), which were abundant in the three plant species. C. ordosica was repellent to C. caragana, which consisted of terpenoids (perillene, a-pinene), esters (dibutyl phthalate), aldehydes (pelargonic aldehyde) and alkanes (pentadecane). No significent orientation selection behavior to C. brachypoda was found, which mainly consisted of esters (cis-3-hexenyl acetate) and olefin (nonylene).3. The EAG and behavior response of C. caragana to five Caragana species were carried out in the labortory. Several compounds could elicit the consistent electrophysiological response, including isophorone (C. microphylla, C. intermedia and C. korshinskii), β-pinene (C. microphylla, C. intermedia and C. ordosica), cis-3-hexenyl acetate (C. intermedia), limonene (C. intermedia), diisobutyl phthalate (C. ordosica), pentadecane (C. microphylla, C. intermedia and C. korshinskii, C. ordosica). The EAG response value of male and female C. caragana increased by concentration of tested compounds. Isophorone and limonene could elicite the largest EAG response, accompanied by diisobutyl phthalate. In behavioural assay, isophorone,β-pinene and limonene were attractive to C. caragana, but cis-3-hexenyl acetate, nonylene and pelargonic aldehyde were repellent to C. caragana.4. The trapping experiment of five blends based on the natural volatile components of five Caragana species was carried out in the field. The blends derived from C. microphylla, C. intermedia and C. korshinskii were attractive to C. caragana adults. However, the blends derived from C. brachypoda and C. ordosica were not attactive to C. caragana adults. Isophorone was a kind of effective attractant to C. caragana in the field. Three-year continuous field population monitoring showed that C. caragana emerged on June 8th for each year and three obvious emergence peaks each year could be found.5. Oviposition detection and selection behavior to five Caragana species of C. caragana were carried out in the labortory. Comprehensive oviposition index was based on 8 oviposition behavior indicators. C. caragana need not bite incisions or supply nutrition before oviposition. C. caragana detected oviposition site by using antenna, maxillary palp, labipalp, foot and ovipositor. C. caragana could oviposit on C. microphylla, C. intermedia and C. korshinskii, but could not oviposit on C. brachypoda and C. ordosica.6. The relationship between oviposition selection of C. caragana and physical structure characteristics of Caragana species were eluciated. Physical structure characteristics of bark surface of Caragana species was crucial to oviposition selection of C. caragana. For C. ordosica, bark surface was wraped tightly by necrotic tissue, which hinder oviposition of C. caragana. Conversely, C. caragana prefered to oviposit on C. microphylla and C. intermedia, which was due to the adaptive bark roughness of the two species. The bark roughness decreased with increase of tree height of C. microphylla and C. intermedia, accordingly, the number of eggs also decreased. The barks of C. korshinskii were smoother than C. microphylla and C. intermedia, the number of eggs was much less, compared with C. microphylla and C. intermedia.7. Type and ultrastructure of antenna, maxillary palp, labipalp, foot and ovipositor of C. caragana were studied. There are seven sensillum types on antenna (sensillum chaeticum, trichoid sensillum, sensilla basiconica, ear shaped sensillum, dome sensillum, plug cone sensillum, Bohm’s mane sensillum), four sensillum types on maxillary palp (sensillum chaeticum, sensillum finger, peripheral sensillum, Bohm’s mane sensillum), three sensillum types on labipalp (sensillum chaeticum, peripheral sensillum, Bohm’s mane sensillum), two sensillum types on foot (sensilla chaetica, trichoid sensillum), three sensillum types on ovipositor (sensilla chaetica, trichoid sensillum, sensilla basiconica). Furtherly, sensillum pedestal (loose, eminentia and tightness), wall structure of sensillum (smooth, with track and cinclides), neuron structure (dendrite acromere, cilium node, dendrite inner segment), secondary cell structure (tormogen, trichogen, spermatogonium) were also studied. All these sensillum was putatively divided into mechanoreception, chemoreception, hygro- or thermo reception sensilla8. Forehead width (the shortest distance between antennal fossa) was the best index used to distinguish larvae instar. In the labortory, half-nature artificial diet of C. caragana was studied. Survival late and growth status were evaluated when larvae raised on artificial diet made from phloem and xylem of five Caragana species. The artificial diet made from C. microphylla, C. intermedia, C. korshinskii and C. brachypoda were fit for C. caragana feeding. The three plant species were classified into susceptible hosts. Conversely, C. ordosica was classified into resistant tree. The correlation between secondary metabolism and nutrient substance of five Caragana species and larva growth status were studied. Secondary metabolism substance of periderm was unrelated to insect damage. In generally, phloem of susceptible tree species contained higher nutrient substances, such as protein, and lower total phenols, flavone and tannin than resistant tree species. Both secondary metabolism and nutrient substance in resistant tree species were higher than susceptible tree species. It was secondary metabolism substances that affect nutrient absorbing and utilizing for C. caragana larvae. In addition, alkaloid may be a kind of synergistic agent to C. caragana.