| Mangrove, a viviparous species growing along the tropical and subtropical coast, is the most important ecosystem of coastal wetlands, and a special forest bridging between land and sea, which is also one of the three main ecosystems to rescue and conserve first in China. However, in recent years, mangrove has suffered severe abuse and was destroyed by enclosing tideland for cultivation, whose distribution area was reduced obviously. Moreover, as Fujian mangrove forests locate in the critical zone of the mangrove-wetland ecosystem distribution in China, the mangrove ecosystem is rather weak, which makes several kinds of insect pests colonization in mangrove forests and causes outbreak on large scales. Herein, from 2000 to 2006, the structural characteristics of insect community for different types of mangrove forests were studied to determine the dominant species of the insect community, to figure out the major insect pests and their bionomical characteristics and population dynamics, and also to explore mechanisms of mangrove chemical defense against major insect pests in the mangrove ecosystem. In addition, the tritrophic interactions among mangrove (host), insect pests and natural enemies were also well investigated, in order to enhance the stress resistant capacity of wetland ecosystems, and to take effective measures to maintain the mangrove-wetland ecological balance, achieving to suppress the insect-pest population density, and as a result, to provide a basis for a theory on the integrated mangrove pest management and the restoration and reestablishment of ecosystems. Furthermore, the biological agents of Bacillus thuringenis and Beauveria bassiana were screened to test which is the more effective agent to contain the major insect pest development, as to provide a scientific guarantee for the sustainable utilization and conservation of mangrove-wetland resources. The main results as follows:Mangrove insect community structure and diversity are the important component on the research of mangrove ecosystems. A systematic investigation was made on the insect community at the port of Zhang river of Yunxiao National Natural Reserve of Mangrove, as well as at the port of Jiulong river of Longhai Provincial Natural Reserve in Fujian Province. At Yunxiao area, a total of 5133 samples were collected and identified, wherein the insecta involved 12 orders, 72 families and 88 species, and the arachnida contained 13 species, while the order of acarid involved 2 species. At Longhai area, 1175 samples were collected and identified, wherein the insecta involved 10 orders, 42 families and 52 species, and the arachnida had 5 species, while the order of acarid had only 1 species. So there were more orders, families and species at Yunxiao area than at Longhai area. However, their distributing characteristics in orders, families and species respectively were very approximate. As for the species distributing in orders, Hymenoptera had the most number of species, accounting for 27．27% of the total species number at Yunxiao area, and next was Lepidoptera, Coleoptera, Homoptera and Diptera, whose cumulative species number occupied 84．09%. Likewise, at Longhai area, Hymenoptera also had the most species number, accounting for 29．09%, and the following was Lepidoptera, Diptera, Homoptera and Coleoptera, which totally occupied 88．46%.The insect groups at Yunxiao and Longhai areas were detected by clustering analysis to be divided into 3 categories. The first was from the regions of the high, middle and low tide levels in Aegiceras cornicelatum mixed forests with Kandelia candel. The second was from 3 different kinds of stands, Avicennia maruna, K. candel and A. maruna mixed with A. cornicelatum. And the third was from the regions of the high, middle and low tide levels in the pure stands of A. maruna. The results showed that there existed different insect communities with different kinds of mangrove compositions. Comparison of diversity index among different insect communities showed that the insect community diversity appeared significantly different in different kinds of mangrove stands, of which the insect community richness in A. cornicelatum mixed forests with K. candel was the highest, and the following was the K. candel pure stands, and the lowest was the A. maruna stands.There were different rules of dynamics of individual amount within mangrove insect community at different tide levels in different stands. At the low tide level of pure stands of A. maruna, there was no obvious peak of individual amount, only fluctuating to some extend. At the high and middle tide levels of pure stands of A. maruna, and at the low tide level of A. cornicelatum mixed forests with K. candel, there were 2 obvious summits of individual amount, i.e. in early and mid-Jul., and during late Sept. to early Oct. Moreover, the amount of insect individuals happened greatly in July. At the middle tide level of mixed forests, the peak in the changing trend of individual amount appeared in May, and subsequently reduced to fluctuate to a certain extend. While at the high tide level, the insect individuals were the most abundant by late June and mid-Aug. The species richness dynamics in mangrove insect community were consistent at different tide levels of A. maruna pure stands, which shaped curve trends with 2 crests and 2 troughs with the temporal sequence, i.e. in early and mid-July, and during late Sept. to early Oct., the insect species richness is the highest in the pure stands. While the richness trends at different tide levels of mixed stands were not consistent with the temporal sequence changing. At the low tide level, the richness increased slowly till late Sept., then reduced subsequently. And the richness trend at the middle tide level was consistent with the pure stands of A. maruna, developing 2 visible peak in mid-and early July, and during late Sept. to early Oct. At the high tide level, there was a crest in early Aug, when insects were the richest. Biodiversity of mangrove insect community was consistent with evenness, diversity and dominant concentration indices in the time sequence. The changing trends of diversity index were consistent at different tide levels in the mixed forests, which all fluctuated between 2 to 4．At the high and low tide levels, there were 2 summits in late July and mid-Oct, which meant the diversity index (H') was maximum, approaching 4．While the summit at the middle tide level was ahead of 20 d. The diversity index of insect community in A. maruna pure stands varied variously, which meant the insect community was greatly influenced by the external environment. The common traits were that the diversity index was lowest in late Aug., which may be caused by the typhoon attack in mid-Aug of the year, and it brought rainstorm to reduce the insect species richness, density and abundance. The insect community of mixed forests was more stable than that of pure stands, and the evenness correlated positively to the diversity index. The tide and storm were the main determinants of mangrove insect community structural level.The main dominant species in mangrove insect community at Yunxiao area were ants, Braconidae and Bethylidae of Hymenoptera, L. cellifera, Ptyomaxia sp. and Latoia lepida of Lepidoptera, planthoppers and Diaspididae of Homoptera, and Phoridae and Ephydridae of Diptera. Because of different insect habits and the chemical and physiological characteristics of different mangrove plants, the dominant insect species were also different in different mangrove stands. Except planthoppers could inhabit and feed on various mangrove plants, most dominant species had high selections for host plants. e.g., an ant could only nest and inhabit in the crown of A. cornicelatum and K. candel, living with Diaspididae. L. cellifera feed on A. cornicelatum. L. lepida only feed on the A. cornicelatum and K. candel at the high tide level. And Ptyomaxia sp. only feed on A. maruna.The vegetative characteristics of mangrove show the regional distribution pattern, that is, visible differences of plant community in mangrove were observed among various areas. The structures and characters of insect communities vary with the different types of mangrove. The study of the main pest insects of mangrove in North China (Fujian) is still unknown. It is urgent to probe the biological and ecological fundamental of the insect pests in mangrove. From 2000 to 2006, we studied the insect pests in mangrove.L. cellifera is one of the main defoliators for A. corniculatum which is the main tree of mangrove, and identified as a new record of species in China. L.cellifera could complete 7 generations a year in Zhangzhou area, Fujian Province, and overwinters as a pupa in the rolled leaves. Adult moths appear in May of the next year, which is the flowering period of A. corniculatum, soon copulating and laying egg scatteringly on the back of leaves. And the first instar of larvae spin to stick 2 to 3 leaves together around apical bud irregularly and feed the mesophyll inside. Mature larvae spin silk to stick leaf margin into the shape of dumpling, then cocoon and pupate inside. The investigation in forests showed that at the mouth of sea the average rate of damage to A. corniculatum by L. cellifera at the low tide level is 50．27%, and the highest could reach 92%. At the middle tide level, the average rate was 17．97%, and the highest was 70．83%. While the distribution of L. cellifera in A. corniculatum was less at the high tide level near the bank, and the average rate of damage was only about 2%, and the highest was 12%. The larvae of different generations distributed in clustering pattern in forests, which was related to the plant resistance and pest habit that A. corniculatum in the front of seaport grew dwarfly and weakly, and L. cellifera could stand soaking in the sea and the moths were not good at flying in the upper air. That was why A. corniculatum at the mouth of sea were injured severely.Ptyomaxia sp. is a destructive defoliator for A. maruna across the conservation areas at Yunxiao and Longhai area, Fujian. These larvae could cause severe damage (100%) to the expanding buds. The apexes of stands turn brown and died, like flames. There are six generations of this species in Yunxiao area. The new hatching larvae overwinter since Nov. in the buds and recover in May. The period of oviposition stage, pupal stage and adult stage are bout 6-7, 14-18, 5-6, and 3-5 d, respectively. Species abundance of the eggs and larvae were fitted to the clustering distributions. Theλ<2 indicated that the population aggregation was caused by the certain environmental factors.L. lepida were one of the severe defoliators in K. candel and A. cornicelatum. The density decreased with the decline of tide levels. Higher damage percentage (46．3%) was found at the high tide level than at the low tide level (13．8%). There are two generations of the L. lepida per year. During May to June, the adults emerge from overwintering to mate and oviposit. The eggs begin to hatch from May to August for the first generation and the second generation occurs since July to the next year. In the lab observation, 99．86% of L. lepida survived within four hours when they were soaked into seawater. No effects of the seawater on the growing of this species, suggesting that L. lepida outbreaks at the high tide level because it developed resistance to seawater.Most serious insect pests in mangrove evolve host-plant specialization, which means the damage level depend on the plants species and their associated insect species. The main insect pests in mangrove are consisting of foliage insects from Lepidoptera and Homoptera. Plant secondary substance tannin and nutrition ingredients comprising sugar, carbon, nitrogen, protein, fat and amino acid were studied to explain the chemical mechanisms.Tannin as the deterrent substance for the insect can impede the growth of insects and decrease the productivity. In the present study, higher tannin contents (33．49%) was found in the B. gymnorrhiza compared with those of A. cornicelatum (25．26%), K. candel (25．28%) and A. maruna (25．35%), which was consistent with our results in the fields. Lower populations of herbivorous insects were found in mangrove forests with higher density of B. gymnorrhiza that contained more abundance of tannin. The seasonal dynamics of tannin in A. maruna was as followed: August > July > April > November. Lower tannins content was found in A. maruna in April or late November when the populations of Ptyomaxia sp. started to appear, however, higher tannins content occurred in July and August, which resulted in less infesting by herbivorous insects.The nutrient substances including contents of water, sugar, nitrogen, carbon, fat, protein and amino acids were tested. The carbon-nitrogen ratio was as followed: B. gymnorrhiza > K. cande > A. cornicelatum >A. maruna. The highest value of C:N ratio and lowest value of protein and amino acides were found in the B. gymnorrhiza. Higher sugar content also was found in the B. gymnorrhiza compared with other plant species, suggesting higher resistance to insect attack by deterring the development and growing of the insects. On the contrary, lower resistance was found in the A. maruna. Our findings indicated that the mangrove might decrease the plant quality to hamper the development of insects and consequently decline the foliage damage.The selection of plant species, natural enemy conservation and the biological control were discussed to explore the effective approaches in IPM in mangrove fields. The effects of Bt and B. bassiana on the Ptyomaxia sp. was carried out in the lab and showed that higher infection percentage was found in Bt treatments than in the B. bassiana treatments. It is necessary to further isolate and purify the B. bassiana strains from the Ptyomaxia sp.. The results of field trials found that the mortalities of Pyralidae after treated with Shudan, Cainong#2 (Bt insecticide) and Shachongwei were 98．1%, 92．7% and 94．74%, respectively. It implicates that biological control is safer and environment-friendly compare with the chemical control.
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