Behavioral Process of Aggregation of the Red-Striped Sawfly, Arge nigrinodosa MOTSCHULSKY (Hymenoptera : Argidae)

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The larval behavior leading to aggregation was observed in the laboratory. Hatchlings just emerged from an egg mass moved toward the tip of a shoot irrespective of the direction of gravity, went into a petiole in turn, and colonized. The aggregation was rapidly formed by all the larvae having this fixed pattern of behavior on a shoot.The following three points were considered essential for the formation of aggregation. Firstly, the orientation of the ovipositing female orients the hatchlings to come out in the upward direction, i.e. in the direction of the tip of the shoot. Secondly, the larvae have the basic habit of moving straight-forward between petioles on a shoot. Thirdly, the direction of light and the direction of the petiole which makes an acute angle with the shoot were recognized as factors reponsible for the change of course in larval movement.