| In recent years, the occurrence of corn diseases and insect pests have been greatly changed andthere have been more and more new pests infesting corn with the increasing of corn planting areas,global warming and transformation of cropping systems in China. Monolepta hieroglyphica, apolyphagous insect pest, less injuring corn before, has become one major insect pests of corn innorthern spring corn region and part of summer corn region. The infested regions and acreage of M.hieroglyphica are gradually expanding in recent years. M. hieroglyphica was often treated as asecondary insect pest with limited studies in China. In order to clarify the occurrence and biologicalcharacteristics of M. hieroglyphica in corn field, and to provide a scientific base for developingintegrated management measures, the population dynamics, spatial distribution pattern occurrence anddevelopmental period of M. hieroglyphica were studied in field and laboratory conditions. The mainresults were summarized as follows.1. Temperature has great impact on the development of M. hieroglyphica, the developmentalduration of egg, larva and pupa at different constant temperatures presents significant differences.Developmental rates of egg, larva and pupa increase greatly with the increasing of temperature rangingfrom19℃to31℃, respectively. According to the degree-day equation between development rate andtemperature, the developmental threshold temperature and effective accumulated temperature of egg,larval and pupal stages were13.94℃and877.19d·℃,11.77℃and450.45d·℃,13.55℃and106.95d·℃, separately. Developmental rate and temperature can be well fitted Logistic Model.According to Logistic model, the maximum developmental rate of the egg, larva and pupa of M.hieroglyphica is0.028492,0.058425and0.188237, individually.2. M. hieroglyphica occurs one generation per year in Shanxi province. Mated female deposit mostof eggs in the top10cm of soil surface surrounding the corn root system where it overwinters bydiapuased egg. The overwintering eggs in corn field of Xinzhou City, Shanxi Province hatch inlate-May and the neonate larvae bore in or make tunnels on corn roots for feeding. The peak period ofM. hieroglyphica larvae is in mid-June and then some matured larvae begin to pupate in soil. M.hieroglyphica adults begin to emerge in late June with peak emergence in early August. The adultpopulation in corn field decline sharply after mid-August when most corn silks wither and the leavesbecome yellow. The M. hieroglyphica adults in corn field are not observed in mid-October, but in weedssporadically. The growth stages of corn in Jinzhong where the rain-fed corn were10days later than thatin Xinzhou where the corn can be irrigated, and also the adults begin to emerge in Jinzhong later than inXinzhou, but the trend of M. hieroglyphica adult population dynamics in the two places were similar. M.hieroglyphica adults mate mainly during10-12a.m. and17-19p.m. time slots in mid-July. Matedfemale lays eggs into soil cracks in1-2days which prefers to the soil surface with high humidity foroviposition.3. The aggregation index k>8shows that the adults distribute randomly but other aggregation indexes show that the M. hieroglyphica adults distribute aggregately in corn plants, at whorl and silkingstage of corn development, respectively. The aggregation index indicates that the distribution pattern ofM. hieroglyphica adults in corn plants at silking stage belong to aggregation distribution. The resultshows that the adults distribute uniformly with the improved Iwao’s regression equation at whorl stage,which in contradiction with the result of aggregation index. The M. hieroglyphica adults distributeaggregately with regression analysis, and the degree of aggregation increases as the population densityrises at silk and milk stage, respectively. The aggregation might be due to the comprehensive effect ofthe aggregate habits of adults and other environmental factors. The distribution laws of M.hieroglyphica adults in corn fields vary with corn development stages. M. hieroglyphica adults mainlyfeed on the upper leaves in whorl stage and the population density of the adults are significantly higherthan that on the lower leaves of corn plants. Adults begin to infest corn silks during silking stage, but thepopulation density of adults feeding on upper leaves is still the highest. Adults mainly feed on corn earsin mil stage.4. The results indicate that the distribution of overwintering eggs of M. hieroglyphica in corn fieldbelongs to the negative binomial distribution and the pattern of aggregation distribution. Theaggregation might be due to the integrated effect of the oviposition behavior of female adults and otherenvironmental factors, including the growth situation of vegetation in corn field, soil properties,temperature and humidity, etc. The eggs of M. hieroglyphica are usually deposited beneath the soilsurface. The soil surface with great moisture and cracks is preferred oviposition sites. It is observed thatthe95%of the eggs are in the top10cm between0to15cm of the soil surface. Tillage and irrigationmethods, soil surface characteristics, soil cracks, soil moisture and earthworm burrows are importantfactors that affect the oviposition behavior of adults.5. Theoretical sampling numbers at whorl, silking and milk stage were specified, and the sequentialsampling table were established according to the sequential sampling model of each stage, m0=1wasthe critical population density. The reliable sampling methods, such as checkerboard and zigzagmethods, both of them can be used in the investigation of population density at whorl and silking stage.Double diagonal lines and checkerboard methods are both reliable sampling methods at milk stage.Five-point method is also a good sampling method of valuation if we just need to know thedevelopmental trend of adults. |
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