木瓜秀粉介殼蟲於四種寄主植物上之生命表

Abstract

木瓜秀粉介殼蟲 (Paracoccus marginatus Williams and Granara de Willink) (半翅目：粉介殼蟲科) 屬於廣食性的害蟲，可為害至少 32 科植物。此蟲雖已知可存活於多種寄主植物上，但於大多數寄主植物上之發育及繁殖型式仍舊未明。本試驗以木瓜、茄子、朱槿及大花咸豐草作為木瓜秀粉介殼蟲於果樹、蔬菜、園藝植物及雜草之代表，將木瓜秀粉介殼蟲及四種寄主植物飼育於 25°C、75-80% RH、光週期 12 :12 h (L:D) 之生長箱。研究結果顯示，木瓜秀粉介殼蟲雄蟲累積發育時間均較雌蟲長，兩性累積發育時間皆於朱槿上最短 (雄蟲22.4日、雌蟲19.0日)，茄子上則最長 (雄蟲27.3日、雌蟲24.8日)。於茄子上之雌雄成蟲壽命分別為 15.2 及 1.3 日，較其他三種寄主植物上之族群短。產卵期、成蟲壽命與存活率與寄主種類並無相關。族群雌性比例於木瓜 (76.1%) 及茄子 (79.7%) 較高，繁殖力也呈現相似趨勢。試驗資料以蟲齡蟲期兩性生命表分析，無論淨增殖率 (R0) 或內在增殖率 (r)，木瓜上之族群 (R0 = 374.7子代數/雌蟲；r = 0.218/日) 皆遠高於其他三種寄主植物，顯示木瓜為木瓜秀粉介殼蟲之最適寄主。利用兩性生命表分析木瓜秀粉介殼蟲於四種寄主上穩定齡期分布之未成熟期比例及穩定齡期分布之雌雄成蟲比例，結果顯示於淨增殖率較高之族群生長的寄主上，族群之雌性比例及穩定齡期分布之雌性比例通常較高，顯示族群雌性比例與寄主適合度具相關性。綜觀上述資料，木瓜秀粉介殼蟲於木瓜上最具族群增長潛力，茄子次之，朱槿及大花咸豐草為適存值較低之寄主。寄主選擇性試驗結果指出，木瓜秀粉介殼蟲對朱槿葉片之偏好性最低，對木瓜、茄子及大花咸豐草葉片之偏好性較高；Y 型嗅覺測試儀結果顯示一齡蟲對寄主氣味幾乎無反應，說明寄主氣味可能非一齡蟲搜尋寄主之主要依據。本研究反映出木瓜秀粉介殼蟲於不同寄主上之生活史介量，並可作為後續擬定相關防治策略使用。

The papaya mealybug, Paracoccus marginatus Williams and Granara de Willink (Hemiptera: Pseudococcidae), is a polyphagous pest feeding on various tropical fruits, vegetables and ornamental plants. Previous observations indicated that P. marginatus can infest up to 32 families of plants, all of which presumably allow survival of the mealybug, yet how it develops and reproduces on various plants remains unclear. To assess the life history parameters of the mealybugs on different host plants, P. marginatus were reared on papaya (Carica papaya L.), eggplant (Solanum melongena L.), hibiscus (Hibiscus rosa-sinensis L.) and hairy beggartick (Bidens pilosa L.) under laboratory conditions of 25°C, 75-80% RH, and a photoperiod of 12:12 h (L:D). Results indicate that males generally possess longer cumulative developmental time than females, and both sexes of P. marginatus have the shortest cumulative developmental time on hibiscus (male 22.4 d, female 19.0 d) but the longest on eggplant (male 27.3 d, female 24.8 d). Longevity of adult females and males on eggplant are 15.2 and 1.3 days, respectively, which are both shorter than those on other three host plants. The patterns of oviposition period, adult longevity and survival rate were found irrelevant to host species. Proportion of female P. marginatus is higher on papaya (76.1%) and eggplant (79.7%), and a similar trend can be discovered for fecundity. Raw data were further analyzed with the age-stage, two-sex life table, the net reproductive rates (R0) and intrinsic rate of increase (r) of P. marginatus reared on papaya (R0 = 374.7 offspring/female; r = 0.218/d) are both the highest over others. Stable stage distribution analyses show that proportions of adult females are generally higher on the host on which P. marginatus possesses higher net reproductive rate, thus suggesting the potential correlation between the proportion of female and host suability. In conclusion, virtually every line of evidence in this study supports that papaya represents the most suitable host plant with most potential for population growth of P. marginatus. Host preference was tested by exposing 1st instar nymphs with leaves of four host plants, and higher preference can be discovered for papaya, eggplant and hairy beggartick but not hibiscus. Y-tube olfactometer bioassays revealed that 1st instar nymphs seem not respond to the odor of each host plant, suggesting that olfaction appears not to function as the primary mechanism for host searching of P. marginatus. Life history patterns of P. marginatus on four different hosts generated from the present study therefore can be baseline information for future development of IPM strategy for this invasive mealybug.