Abstract There was a definite vertical distribution of spiralling whitefly on the guava plant for immatures occurring on the surface of the guava leaves. Eggs and young nymphs occurred on the uppermost and youngest leaves while aged nymphs and pupae were found on older and lower leaves. According to these relationships, sample position for each stage on different sequence leaves was determined.
An analysis of the pattern of spatial distribution of spiralling whitefly on the sampled leaves revealed that egg circles were of the aggregative type. While nymphs or pupae a random distribution.
The optimal sampling size for each developmental stage of the whitefly was estimated by m-m analysis. At the egg circle density of 0.5 circles/leaf, sample size of 122 and 20 leaves were required to fulfill a precision level of 0.1 and 0.25, respectively. Whereas, 408 and 65 leaves were required for the 2nd instar；397 and 63 leaves for the 3rd instar and pupa.
摘要 螺旋粉蝨 (Aleurodicus dispersus Russell) 自卵至蛹各蟲期於番石榴植株之幼至老之葉片上呈垂直分布，即卵及幼齡若蟲分布於上位幼葉上，老齡若蟲及蛹則分布於下位老葉上。調查時作適當部位取樣，可減少誤差。分析取樣葉片間之空間分布，由10g s2-log m關係式，得知卵圈、若蟲及蛹之斜率(b)分別為1.7524、1.0452及1.2456；由m-m關係式得知其斜率(β)為1.1291、1.0048及1.0313，判定其卵圈為聚集型，若蟲及蛹傾向於逢機型。田間取樣數的估計，卵圈之密度設定為0.5圈/葉，精密度為0.1及0.25時，取樣數各為122及20葉片；若蟲與蛹之密度為0.5隻/葉，所需樣品數則二齡若蟲為408及65葉，三齡若蟲與蛹為397及63葉。
| Key words: Aleurodicus dispersus, spiralling whitefly, spatial distribution, sampling size. | | 關鍵詞: 螺旋粉蝨、空間分布、取樣數。 |
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