| Wuqi County, Shaanxi Province, is the major planting area of sea-buckthorn, Hippophae rhamnoides. The larvae of Trabala vishnou gigantina is a major defoliator pest that damages the sea-bucktorn. Although T. vishnou gigantina has numerous hosts, in the sea-buckthorn forests of Shaanxi Province, the moth appears to use sea-buckthorn exclusively, despite the presence of other potential host plants (including apricot, poplar, willow, caragana, and locust). In this paper, we focused on the feeding preferences of T. vishnou gigantina larvae on six sympatric plant species. Spectroscopy technology was used to confirm the physical and chemical factors of host selection of T. vishnou gigantina larvae. Based on feeding preferences we also compared T. vishnou gigantina fitness, as measured by the following variables: performance, fecundity and nutrition utilization indices. Fitness indices and the major nutrition compounds, secondary metabolites of six plants were combined for the integrated evaluationg of the host plant quality. The study involved with nutritional utilization and enzymes activity on shifting host of T. vishnou gigantina larval, it was affirmed the nutrition value of the larvae changing the host plants, and affirmed that the activy of the change of enzymes in the larvae was one of the main reasons why the larvae increase the scope of host plants. The main results are summarized as follow:1. The results clearly demonstrate that T. vishnou gigantina larvae were able to distinguish between different plants. We observed the feeding preferences of T. vishnou gigantina larvae on six sympatric plant species in the labortory. Between host and non-host plants, larvae showed a strong preference for sea-buckthron, followed by apricot, poplar and willow in order, caragana and locust were the least preferred plants. We found that the order of preference to different plant species for larvae with different host plant experience and starvation time was consistent with that of the larvae collected in the wild. Our study also showed that feeding preference of larvae was not correlated with the oviposition preference of adults.2. The effect of chemical and physical structure of six plants on T. vishnou gigantina larvae feeding preferences was carried out by spectroscopy technology. The Fourier Transform Infrared (FTIR) spectroscopy analysis displayed that those six plants presented similar characteristic on absorption peak position, peak amount, and shape. The results showed that lipids and polysaccharide were major nutriments to affect the feeding preference of T. vishnou gigantina larvae. The crystallinity index (CrI) of six plant species was conducted, the results showed that T. vishnou gigantina larvae preferred to plant species with low degree of crystallinity.3. We compared T. vishnou gigantina fitness, as measured by the following variables: larvae weight, developmental period, pupae versus adult weight, longevity, and fecundity rates. Sea-buckthorn or apricot-reared larvae were significantly heavier than those reared on both poplar and willow throughout the experiment. Larvae reared on sea-buckthorn possessed greater pre-pupal weight, had lower mortality, and developed more quickly into heavier pupae than either poplar-raised or willow-raised larvae. Fecundity was highest on sea-buckthorn, second highest on apricot, and lowest on poplar. Longevity (of both females and males) was not significantly different across plant species. Overall, several fitness indices of T. vishnou gigantina larvae were combined for evaluation of the host plants quality, the most suitable host plants was sea-buckthorn, followed by apricot, poplar and willow were the worst suitable host plants.4.The relationship between larval development fitness indices and host plant inclusion contents was analyzed. Nutrients, water and secondary compounds differed significantly among the different host plants. Soluble sugar content was significantly, negatively correlated with female pupal weight and fecundity, and soluble protein content was significantly negatively correlated with duration of the larval duration. Female and male pupal weights were positively correlated with water content. There was no relationship between flavone content and the larvae duration or adult fecundity, but tannin content was significantly positively correlated with the duration of pupal stage.5. Larvae nutrition utilization on different host plants were significantly different as to differetn experiment parameter, including relative consumption rate(RCR), relative growth rate(RGR), efficiency of conversion of ingested food(ECI), efficiency of conversion of digested food(ECD) and approximate digestibility(AD). RCR, ECD and ECI in larvae feeding on sea-buckthorn was significantly higher than that on the other three plants, the ECD and ECI in larvae feeding on apricot and willow were higher, but the AD was lowest. From RCR index perspective, the increased RCR was necessary for larva to consume on lower AD that was raised on apricot. Increased AD or ECI was impossible for larvae to consume lower RCR that feeding on poplar and willow. It is concluded that poplar and willow were the worst suitable host plants.6.Obvious differences were determined in the activity of detoxifying, protective and digestive enzymes of T. vishnou gigantina larval, which might partly reveal the physiological adaption after host shifting. The results indicated that feeding on different host plants significantly affected the enzymes activity of corresponding larvae. The glutathione S-transferase (GST) activity in the larvae fed with sea-buckthorn and aprioct was highest after feeding 12h. However, the glutathione S-transferase activity in the larvae fed on poplar and willow was highestat after feeding for 36h. The variation trend of the tatal acetylcholinesterase (TchE) activity fed on sea-buckthorn was not obvious with feeding times increase, but the levels of TchE activity fed on poplar and willow were found to be the highest after feeding 24h, and fed on apricot was found to be the highest at 12h, while TchE activity had no significant difference after feeding 48h. Our results showed that the changes of detoxifying enzymes led to adaptation to new host plants.The result showed that the activities of digestive enzymes in larvae feeding on different host plants were differents. Shifting from sea-buckthron to apricot, poplar and willow, the protease activity of larvae were restrained significantly, and increase with feeding time. The changes of amylase activity of larvae that fed on apricot and poplar were not obvious with feeding time increase, while feeding on the willow with 6h was rapidly increasing. The changes of lipase activity that fed on different plants was no obvious. Thus, the results showed that the activity of digestive enzyme increased with the protein and the dextrose content, eventually leading to different host adaptability on differ host plants.7.Sensors on the head of T. vishnou gigantina larvae were observed though scanning electron microscope, compared with other lepidoptera larvae the types, numbers, and distribution of sensilla on the larval head were similar. Three types of sensilla were observed on the antennae of T. vishnou gigantina larvae, including only one sensilla styloconica,5 sensilla basiconicums and two sensilla chaeticas. There are 8 sensilla styloconicums on larvae palpus,2 bigger sensilla styloconicas and 4 sensilla trichodeas were observed on the palpifer. One sensilla styloconica and one sensilla chaetica were recorded on labipalp. |
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