A Comparative Study On The Differences Of Diapause Characteristics Among Different Geographical Populations Of Small Brown Planthopper

Diapause is a common used seasonal strategy of insects in response to adverse environmental factors. During diapause period, insect development is ceased. It is induced by some internal factors (genetic and hormonal regulation) and external factors (environmental factors such as photoperiod, temperature, humidity, etc.). Small brown planthopper (SBPH) is an important rice pest and worldwide distributed throughout East Asia, Southeast Asia, Europe and North Africa. In China, it spread all over the country. The difference in climate and agricultural productions of China might cause the geographic differentiation of biological characteristics in SBPH. Diapause is one of successful strategies for SBPH to adapt to extreme environments. The geographical difference of diapause in SSB still remains unclear. Here, we studied the impact of light and temperature on diapause induction, diapause termination, physiological and biochemical characteristics and biological features of different SBPH geographical populations (Kunming, Shenyang, Zhengzhou, Nanjing and Jiaxing). The results provided theoretical basis for life history of different geographical populations. It is of great helpful for the comprehensive governance and agricultural production of SBPH populations. The results are as follows:1. Determining the diapause criteria of SBPH individuals. The developmental period of diapause SBPH in five populations were longer than25.5days,24days,21days,23days,23.5days for Shenyang, Zhengzhou, Nanjing, Jiaxing and Kunming populations, respectively. Otherwise, it is non-diapause individuals.2. Clarifying the main diapause stages of SBPH nymph in different populations. The3rd instar nymph is the sensitive development period of SBPH. More than55%of SBPH enter into diapause at this stage. Where as only10%of SBPH begin to diapause at the4th instar nymph. The percentages of the2nd instar diapause nymphs are higher in Kunming, Shenyang and Nanjing than that in Zhengzhou and Jiaxing. The Jiaxing population has the lowest percentage of the5th instar diapause nymphs, but there is no statistically significant difference with other populations.3. Clarifying the key factors inducing diapause of SBPH in different populations. The most important factor inducing SBPH diapause is temperature. When it is≤16℃, all SBPH entered into diapause, regardless of photoperiod. SBPH belongs to short photoperiod diapause type. The photoperiod of8L:16D,10L:14D,12L:12D induce the diapause of SBPH. Nanjing population is the most sensitive population to start diapause, followed by Shenyang, Kunming, Zhengzhou and Jiaxing. The interaction of photoperiod and temperature has higher impact on SBPH diapause than photoperiod. The photoperiod mainly influences striatellus diapause by interacting with temperature.4. Clarifying the optimum conditions of SBPH diapause in different populations. The temperature of25℃and16L:8D is the most effective condition in inducing diapause, followed by25℃and8L:16D. At condition of16℃and16L:8D, the diapause period of SBPH is longer than that of25℃and8L:16D. High temperature and long photoperiod promote diapause period. Temperature plays a key role in terminating diapause of SBPH.5. SBPH belongs to glycogen accumulation type. The total sugar, glycogen, trehalose and glycerol are decreased with development in both diapause and non-diapause SBPH. The content are not significantly different in diapause and non-diapause nymphs. The content of total proteins in diapause nymphs is higher than that of non-diapause nymphs. In diapause period, total body protein content decline first and then increase. The total amino acid content of diapause SBPH remains constant from the3rd instar to the4th instar nymphs. But it increases significantly after the4th instar. However, the total amino acid increases continually from during whole nymphs period.6. Validating the biological characteristics differences in SBPH of different geographical populations. The statistical results of body length of both male and female are in line with the Bergmann rule. The body becomes small from high latitude to low latitude region. The statistical results of sex ratio show that male number is much more than female in Shenyang population. The proportion of long-winged female reduced with the decrease of latitude. The female proportion of SBPH in Shenyang population is low and the most are long wings. In the range of19-28℃, the rate of development increased with the temperature in different populations of SBPH. At31℃, the developmental period significantly increased, especially in Shenyang and Zhengzhou populations. In the range of19-31℃, adult life of SBPH were shortened with the increase of temperature. However, there is no statistically significant difference in Shenyang, Zhengzhou and Jiaxing populations. The adult life span of Nanjing population was the longest from19℃to25℃, and it is shorter at28-31℃. Except Shenyang population, the fecundity of other four populations of SBPH was the largest at28℃and can not lay eggs under30℃. In the range of22-28℃, the effective fecundity of Shenyang population decreased with the increase of temperature. At28℃, Nanjing population has the highest fecundity, followed by Shenyang, Zhengzhou and Jiaxing.