| During 2013-2014, we investigated the insect pests and natural enemies of lucern(Medicago sativa L.) field in Kangbao County of Zhangjiakou City, Hebei Province. Our study made clear the species diversity of insect pests and natural enemies, population dynamics of their dominant species on lucern. The Polymerus pekinensis Horváth was found one of the dominant species, and its basic biology was also illustrated. In addition, we defined the prevention and control index of Loxostege sticticalis Linnaeus, a potencial outbreak pest to lucern, and demonstrated the basic biology and control ability of its two parasitiods: Orgilus ischnus Marshall and Zele chlorophthalmus Spinola. The results were as follows:1. Totally, 95 species of insect pests were found through more than one year field investigation and belonged to 7 orders and 26 families, including 21 Hemipteras, 36 Coleopteras, 18 Lepidopteras, 13 Homopteras, 1 Diptera, 6 Thysanopteras, and several Orthopteras. There were 43 species first discovered on lucern in China, including 5 Homopteras, 8 Hemipteras, 26 Coleopteras and 4 Thysanopteras. The largest number of individuals was Homoptera, accounting for 68.31%,and next was Hemiptera, accounting for 17.43%. It is worth mentioning that Coleoptera had the maximum species, but the total number of individuals accounted for only 7.27%. Therioaphis trifolii(Monell) ranked as the 1st Dominant species of lucern pests, the dominance degree of which was up to 0.5841, followed by Nysius ericae(Schilling), 0.0822, and the 3rd ranking dominant species was P. pekinensis, 0.0596. Natural Enemies mainly composed by 6 ladybirds, 7 predatory beetles, 4 predatory bugs, 3 lacewings, 2 flies, ants and spiders.2. Our research made clear the population dynamics of main pests and natural enemies in lucern, the structure characteristics of insect pest community.1) The population dynamics of main pests: The population of T. trifolii was the highest on July, and the more rainfall, the higher relative humidity and the lower temperature, the less occurrence of T. trifolii will be. Occurrence period of N. ericae was more concentrated, mainly from mid-June to early July, and occasionally in other periods. P. pekinensis had 3 generations per year and overlapped between the generations. It caused damages from April to September, and high occurrence periods were in late May and late July. P. striatus brought severe damages at later growth of lucern, and the peak of population was around August 17.2) The population dynamics of natural enemies: the occurrences of Orius minutus(L.), Geocoris ater(Fabricius) and Nabis feroides mimoferu Hsiao were all from early July to mid-September, and the individuals reached the maximum at August. Two occurrence peaks, late June and mid-July, existed in the dynamics of ladybirds. From mid-May to early September the population of ants was on the rise, up to highest at September 7. Overall, the occurrence of natural enemies was followed with the population dynamics of insect pests.3) Applied Richness S, Richness index D, Diversity index H, Simpson Index C and Pielou evenness index E to analyze the the structure characteristics of insect pest community. The richness S was high from June 22 to July 13(33-36), indicated that there were more pests occurred at June and July. The index D ranged at 0.789 ~ 5.419, variable among mouths, and was higher from June 8 to July 16, in accordance with the result of richness S. The index H reached the highest at early June, after decreased gradually, and was the lowest in September. The results shown that there were more pest occurrence from June to early July and fewer happened in September. Index C reached highest at September(>0.800), and was the lowest at early June(<0.200).The results shown that some species were prominent in quantity. Index E was the highest at June and the lowest at September. It proved that the number of individual among different species distributed well in mid-June, but significant uneven in September.3. First study on the biology of P. pekinensis. There are 5 instars of nymphs for P. pekinensis, and the result of development time of 1-5 instars shown that 5th instar nymph was the longest one(4.8d). The total development time for nymphs was about 17 d. The mean pre-oviposition period of female was 11.38 d, and the Oviposition period was about 9 d. Egg stage was about 15 d in temperature 23℃. Generation duration was about 43 d. In addition, the mean longevity of adults including male and female, were 36.11 d and 36.41 d, respectively, and there is no significant difference between the genders(P=0.94).,4 Used two methods to study the relationship between the larvae density of L. sticticalis and the yield loss of lucern, formulated the prevention and control index of L. sticticalis. The artificial inoculating method obtained the linear regression equation was: y= 2.9954x-2.8166(R2=0.9836,P=1.1817E05). Lucern was mowed once or twice in Kangbao County, and the prevention and control indexes of L. sticticalis were 12 and 19 larvae per 100 branches. The other method of feeding amount also obtained a linear regression equation and it was y=3.1692x-0.0258. Similarly, the prevention and control indexes of L. sticticalis were 7 and 14 larvae per 100 branches when mowed once and twice of lucern, respectively.5 The developmental period for egg and larvae, pre-pupae and pupae, and whole generation of O. ischnus was 12.8, 10.5 and 23.2 d, respectively. Cocoon of the wasp weighted 4.1mg in average. The wasps mated immediately after emergence; with an average duration of 49 s. Female wasps oviposited soon after mating and peaked at the 1st 4 d and 8th d of the wasp life, with lifetime fecundity more than 100.5. The female and male wasps lived 11 and 14 d, respectively when honey solution was supplied. Number of the host parasitized by O. ischnus increased as the host density increase while the actual parasitic rate decreased with the increase of host density. The maximum numbers of host parasitized daily and the optimal searching efficiency for the wasp was 25.1 and 9.3, respectively, which fitted with Holling type II and III. The food consumed by the parasitized and normal larva was 106.7, and 499.8 mg, respectively. The body weight and size of the parasitized larva was significantly less than the normal larva at the 6 and 12 days after parasitizing. The developmental period for egg and larvae, pre-pupae and pupae, and whole generation of Z. chlorophthalmus was 14.7, 14.5 and 30.1 d, respectively. Cocoon of the wasp was 18.01 mg in average. The wasps mated immediately after emergence; with an average duration of 101 s. Female wasps oviposited soon after mating and peaked at the 3rd and 8th d of the wasp life, with lifetime fecundity more than 104. The female and male wasps lived 15 and 19 d, respectively when honey solution was supplied. Number of the host parasitized by Z. chlorophthalmus increased as the host density increase while the actual parasitic rate decreased with the increase of host density. The maximum numbers of host parasitized daily and the optimal searching efficiency for the wasp was17 and 7.56, respectively, which fitted with Holling type II and III. |
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