(8(1):44-54)BIONOMIC STUDIES OF RICE WEEVIL, SITOPHILUS ORYZAE LINNAEUS

穀象在臺灣發生為害情形僅次於穀蠹，但在糙米期則穀象常較穀蠢為嚴重，其繁殖迅速，生活史不甚整齊，本觀察自1951年6月至1953年10月在臺北進行，茲將觀察結果提要如下數點。 1. 穀象卵期最短為3日而最長10日平均為4.7日。卵之孵化率98%以上。 2. 幼蟲各齡期間自3~21日不等平均4.7日，幼蟲全期最短15日而最長29日，平均19.2日。 3. 前蛹期1~2日，平均1.3日。 4. 蛹期間最短3日，最長13日，平均為6.1日。蛹化率為98%。 5. 1雌蟲之產卵數，成蟲每日產卵數，通常2~7粒，1雌蟲產卵總數最少4粒而最多356粒，平均186粒。 6. 成蟲性比雌蟲平均佔46.8%。成蟲壽命雄者較雌者長，雌蟲9~139日，平均94.9日而雄蟲自12~230日，平均為113.6日。 7. 穀象在臺灣，年生8世代，第一世代由2月下旬至4月中旬，第二世代4月下旬至5月中旬，第三世代5月下旬至6月下旬，第四世代7月上旬至7月下旬，第五世代8月上旬至8月下旬，第六世代9月中旬至10月上旬，第七世代10月中旬至11月下旬，第八世代12月上旬至翌年1月下旬。 8. 1世代之歷期，最短20日，越冬期間最長50日，平均需32.2日。 9. 成蟲繁殖力，頗受季節及溫度之影響，在9月間開始飼養繁殖結果，經3個月之繁殖後，以一對成蟲最少能繁殖78頭，最多550頭，平均306.3頭，在11月上旬開始繁殖，經過3個月後最少繁殖數，在138頭，最多246頭，平均184.4頭，經過6個月，最少678頭，最多2,904頭，平均2,171.2頭，9了固月後最少3,878頭，最多6,867頭，平均5,301.3頭，經過1年，最少6,596頭，最多11,036頭，平均8,475.2頭。以上之成蟲數係包括已死蟲在內。 10. 被害損失量之估計，成蟲1對，在1年中之繁殖為害後，在供試720g糙米，經1年後之損失量最少450,3569，佔62.55%，最多571,5789佔79.39%，平均500,5879佔69.53%，其為害情況之估計，若200對成蟲繁殖為害，在1年後約可取食100公斤糙米，可見其為害之嚴量也。 Inrestation of rice weevil Sitophilus oryzae Linnaeus was the only inferior to rice bostrychid Rhizopertha dominica Fabricius in Taiwan. But due to its quick reproduc. tion and overlapped each stage was much injurions rice bostrychid. This observation was carried out at Taipei, Taiwan from June, 1951 to October, 1953. The results might be briefly summarized as follow: 1. Egg stage took 3-10 days, 4.7 days in average; percentages of egg hatching was more than 98%. 2. Each larval stadium took 3-21 days, 4.7 days in average; total larval stage took 15-29 days and 19.2 days in average. 3. Prepnpal stage toon 1-2 days and 1.3 days in averag. 4. Pupal stage took 3-13 days and 6.1 days in average; precentage of pupation was 98%. 5. Number of eggs laid by one female within 24 hrs was 2-7 usually; total number of eggs laid by one female was 4-356, and 186 in average. 6. Sex ratio female was 46.8% in average; adult duration of male wale longer than female, i. e. 9-139 days and 94.9 days in average of female and 12-230 days and 113.6 days in average of male respectively. 7. Rice weevil had 8 generations annually. End of February to mid of April was the 1st generation, end of April to mid of May was the 2nd generation, end of May to end of June was the 3rd generation, first to end of July was the 4th generation, August was the 5th generation, mid of September to first of October was the 6th generation, mid of October to end of November was the 7th generation, end of December to following end of January was the 8th generation respectively. 8. Period (or days) of one generation, the shortest was 20 days, the longest 50 days and 32.2 days in average. 9. Reproductivity of adult was much influenced with the seasonal and temperatue interference. According to rearing data one couple of rice weevil from September to its following 3 months gave 78-550 individua1s and 306.3 inaverage; from first of November to its following 3 months gave 138-246 and 184.1 in average; 678-2,904 and 2,171.2 in average following 6 monthe; 3,878-6,867 and 5,301.3 in average following 9 months and 6,596-1,1036 and 8,475.2 in average following 12 months or one year respectively. The dead individuals were not included in the above data. 10. Estimation of injuried loss was taken one couple of adults let them reproduce and feed freely over one year in given 720g. brown rice, the loss was 450g. i. e. 62.55 % 571g. or 79.39% and 500g. or 69.53%. If put 200 couples of rice weevil in brown rice, they will consume 100kg. of brown rice over one year and shown its injury was so severe