| As a member of Pyrus family, pear has a strong ability to adapt to soil. It can obtain a high yield under a common cultivation and management condition. In addition, pear trees usually have a long lifetime which means that they have much more economic return compared with other fruit trees. As a result, many farmers choose to plant pear trees to increase the income. The continuing high yield of pear plays a significant role in the development of countryside. It can boost diversified economy, help to get full use of local land resources, and help peasants with the income increase. However, due to the limitation of resource and technology, as well as the lack of professional and technical persons in rural area, most pear orchards use extensive management method. As a result of being attched by Janus Piri, Nephoteryx pirivorella and otherlepidopterous larvae, they meet a huge decrease in output. In conclusion, it is very nessesary to perform the pear pest control.Chemical control was easy to use and usually had a quick effect. It played a significant role in ensuring yield stabiliy of food, fruit, vegetable and other crops. Also, the huge initial investment and technical requirement of biological control made it difficult in extension. So chemical control was very common in China, especially in the rural area. However, the improper use of chemical control can lead to a series of problems. It caused plant phytotoxicity, making pests get drug resistance, and kiled beneficial organisms. Futher more, the high pesticide residues even caused evironmental pollotuion to some extent. This paper took the pear orchard in mountain area of North Hebei as a study object, started from the point of whether the pesticides should be used. It analysed the composition of species, community structure, biodiversity, as well as the seasonal dynamic variety in this area, tried to find the impact chemical pesticide had caused on each parameter of anthropod community. In addition, arthropod community was divided into two categories, pest and natural enemy. It evaluated the effect of chemical control from two aspects, controling of pests and the hurt to natural enemies. The major results were as below:(1)In total, 1551 individuals were captured in canopy of pear tree which belong to 107 groups. The dominant group was Camponotus. 16 groups mde up the common groups, occupying only 14.85 percent of the total number of groups but more than half percent of the total individuals. Rare groups ocuppied only three in ten of the total individuals but accounted for 84.11 percent of the total group number. The individual number and group number of arthropod in forest crop intercropping were less than which in canopy, only 636 individuals belonging to 39 groups. The dominant group was Camponotus and Mono Moriu-m pharaonis. The 14 common groups made up 35.90 percent of group number and accounted for 30.35 percent in total individuals. Compared with canopy, the percentage of rare group was relatively less, occupying 53.85 percent of group number and 9.75 percent of individual number.(2) The group number, individual number and biodiversity index D 、 H’ 、 d of arthropod community in canopy all showed a rising trend by time. The seasonal dynamic of evenness index was different, presented as August > June > July > May. Group number and individual number in July and August were significantly higher than which in May and June(P < 0.05). The maximum group number and individual number of arthropod community were in August and July. The difference of D、H’、d and Jh in each month was notable(P < 0.05). The seasonal dynamic behavior of group number, individual number and d of arthropod community in forest crop intercropping were presented as June > August > July > May(P < 0.05). The seasonal dynamic behavior of evenness index showed little difference, June > August > July = May(P = 0.004).(3) The effect of chemical control on arthropod community in the pear orchard of North Hebei was significant. The group number in canopy of pear trees decreased from 109 to 29 after the chemical control. In addition to Camponotus, Apidae, Monomorium pharaonis and Harmonia axyridis also became dominant groups. The group number in forest crop intercropping decreased from 31 to 22 after the chemical control. The number of dominant groups enlarged. After the chemical control, all index of arthropod community in canopy decreased dramatically except Jh(P < 0.05). The decrease of group number, individual number and d of arthropod community in forest crop intercropping was also significant(P < 0.05).(4) Excluding Aphidoidea, 454 individuals in canopy of pear trees, belonging to 57 groups, were classified to pest sub community, accounting for 29.27 percent of total individual number and 53.27 percent of total group number. 17 groups were classified to pest sub community in forest crop intercropping, accounting for 18.08 percent of total individual number and 43.59 percent of total group number. The effect of chemical control on pest sub community of the pear orchards in mountain area of North Hebei was significant. Take the Aphidoidea for example, the damage of Aphidoidea used to be serious. They gathered in, feeding on young shoots and were innumerable to count. Spraying had brought an obvious effect, we found no aphids in HF plots. After the chemical control, group number, individual number and diversity index of pest sub community had decreased significantly(P < 0.05) and meet a high declining rate.(5) In total, 325 individuals in canopy of pear trees, belonging to 27 groups, were classified to natural enemy sub community. They are accounted for 20.97 percent of total individual number and 25.23 percent of total group number. 54 individuals were classified to natural enemy sub community in forest crop intercropping which belong to 10 groups. The natural enemy sub community accounted for 18.08 percent of the total individual number and 43.59 percent of the total group number. After the chemical control, the number of group and individual of natural enemy sub community both in canopy of pear tree and forest crop intercropping decreased dramatically(P < 0.05), biodiversity index(D、H’、d) decreased significantly(P < 0.05), dominance index(C)(P < 0.05) and evenness index(Jh) increased. From the specific data, the effect of chemical control on natural enemy sub community was obvious. In canopy of pear tree the decreasing rate of group number ranged from 46.15% to 88.24%. The decreasing rate of individual number was higher, ranged from 76.52% to 96.90%. The effect of chemical control on in forest crop intercropping was more significant compared with that on canopy. The group number(25.00% to 75.00%) and decreasing rate(61.54% to 85.71%) were even higher than that of pest sub community. As a conclusion, chemical control has an obvious effect on natural enemy sub community, especially on those in forest crop intercropping. |
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