Field observations on the vertical distribution of the cotton leafworm, Spodoptera littoralis (Boisd.) on cotton plants

The populations of early instar larvae of the cotton leafworm Spodoptera littoralis (Boisd.) on certain cotton plants differed from one region to another. The upper region harboured the highest population (about 80 %), only 15 and 5 % were observed on middle and lower regions respectively. The populations of late instar larvae fluctuated considerably within each region and from one region to another during day time and night. More than 80 % of these larvae were found on the upper region between 12 m. and 3 a.m., but the lower region harboured almost the whole population of larvae between 12 n. and 3 p.m. During the latter period, larvae in both the upper and middle regions were less than 5 % each. The population of larvae on the middle region was relatively lower than that on both the upper and lower regions. Fluctuations in the population of larvae on different regions of plant during times of inspection were correlated with the up and down movement of them. Zusammenfassung Beobachtungen über die vertikale Verteilung der Baumwollblatteule, Spodoptera littoralis (Boisd.), im Baumwollbestand Die Zahl der jungen Spodoptera ‐Raupen war in den verschiedenen Vertikalzonen des Baumwollbestandes verschieden. Die oberste Region umfaßte etwa 80 %, die mittlere 15 %, die unterste 15 % der Raupen. Die Populationen des letzten Raupenstadiums zeigten beträchtliche Fluktuationen innerhalb einer Region sowie von einer Region zur anderen zwischen Tag und Nacht. Über 80 % der Raupen wurden in der obersten Region zwischen 12 h und 15 h gefunden, jedoch versammelte sich fast die gesamte Population zwischen 24 h und 3 h früh in der untersten Region. Die mittlere Region beherbergte für alle Tagesund Nachtzeiten die geringste Zahl der Raupen.