| Galeruca daurica Joannis is an important leaf-eating pest that has recently been outbroken on Allium spp. in the lilaceae family in the Inner Mongolia Grassland Region. As the climate and ecological conditions have changed, the damage of G. daurica has been gradually serious. Therefore, it is of great significance to research on the life cycle and occurrence of G. daurica. It helps us to know the development mechanism and increase the pest control effect. In order to clarify the occurrence and biological characteristics of G. daurica and to provide scientific basis for developing integrated management, the population dynamics, spatial distribution pattern occurrence and development period of G. daurica were studied in grasslands and in laboratory conditions. The main results were summarized as follows:1. G. daurica occurred one generation each year in Inner Mongolia. The female deposited their eggs into cow dung or stone for overwinter. Overwintered eggs hatched in the middle or late April in next year. The larvae have three developmental stages, feeding by the stems and leaves of the genus Allium(Allium mongolium Regel、Allium polyrhizum Turcz ex Regel、Wild Chinese chives) to complete their development. Larva occurrence peak happened in climax in late-May, some mature larvae started to pupate, and it is a peak damage period. Adults started to emerge in early-June, fed in some period and started to oversummer in late-June. The adults hid in the cow dung or bushes, almost didn’t feed through the summer, and started to mate in middle-August or last-August and laid eggs in early-September.2. The spatial distribution pattern was analyzed by two regression models and nine indices of aggregation. The results indicated that G. daurica population is an aggregated distribution in grasslands.3. We investigated the effects of13common forage plants on the larval development, survival and feeding amount in the lab. The results showed that the larvae was a specialist herbivore, mainly foraging the genus Allium i.e. A. mongolium Regel, A. ramosum L. and A. polyrhizum Turcz. Ex Regel. and the other test plants were seldom eaten. The above Allium plants had significant effects on the larval and nymphal development durations and no significant effect on the larval survival rates. When fed on A. mongolium, A. ramosum and A. polyrhizum, the larval and nymphal development durations were24.27d,27.87d, 33.13d and6.61d,7.40d,8.43d, respectively, and the larval feeding amounts were393.76mg,442.51mg and496.09mg(fresh weight), respectively. The feeding amounts of3rd instars was the largest, accounting for63.45%～67.46%in the whole larval duration, about3times for2nd instars and5times for lstinstars. Therefore, A. mongolium is the most suitable host plant for G.. daurica larvae, secondly A. ramosum and finally A. polyrhizum. Spraying insecticide should be applied before the3rd instar when chemical control is necessary.4. We studied the effect of six constant temperature (13,17,21,25,29and33℃) on the threshold temperature and the effective accumulated temperature of G. daurica. The results showed that the development period was shortened with the increase of temperature in the range of test temperature. At the temperatures of21,25,29and33℃, the1st instar larval development durations were8.9,7.23,6.8and6.1d; the2nd instars were9.59,7.12,6.76and5.47d; the3rd instars were16.33,14.47,12.87and10.6d; the total larval development durations were30.33,27.83,26.25and25.25d; the nymphal development durations were10.93,7.33,5.87and5.83d, respectively. The development threshold temperatures of1st instar,2nd instar,3rd instar, total larva and nympha were6.3,4.59,11.2,13.75and9.47℃, respectively. The effective accumulated temperatures were237.9,156.3,357.8,745.9and119.6day degree, respectively. The maximal fecundity of females was at23℃. The suitable temperature range for G. daurica was21-29℃. |
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