Item

Abstract

The nesting behaviour of Trypoxylon rogenhoferi was studied in a whitewater inundation forest
(várzea) of Central Amazonia. Nests were constructed in artificial nesting sites ("trap-nests") made of wood
drilled longitudinally to a depth of 80 mm with apertures of 9.5 mm and 12.7 mm diameter respectively.
The nest architecture and most of the behavioral characteristics of T. rogenhoferi generally were similar
to those observed in other species of the genus. The nests consisted of a linear sequence of prey stocks
separated by mud partitions. Nesting activity was greater in the 9.5 mm diameter traps than in the 12.7 mm
diameter traps. Observations of the behaviour of immature T. rogenhoferi provide answers to questions
posed by some authors, such as the use of mud in the construction of the cocoon wall. The larvae of T. rogenhoferi take bits of mud from the internal wall and mix them with the silk mesh to form a girdle
around the body. The mud from the girdle is subsequently spread throughout the cocoon wall. Another
question relates to the function of the mud deposited by the female at the innermost cavity, the preliminary
plug. It was observed that the larvae produce a fragile-walled cocoon if a source of mud is not available.
The preliminary plug in a nest serves as a source of mud for the larva of the first cell. The cells were provisioned with Alpaida veniliae (KEYSERLING) (Araneidae) only. Males, in contrast to females,
developed in the innermost cells and were more abundant in the 9.5 mm diameter nests. The hatching rate
from the cells provisioned by T. rogenhoferi was 41 %, mortality from unknown causes was 38 %, and
mortality due to parasitoids was 21 %. The parasitoids most frequently involved in the destruction of cells
were Pleurochrysis postica, P. morosa, Neochrysis lecointei and two unidentified species of Caenochrysis
(Hymenoptera, Chrysididae; 60.7 %), followed by Lepidophora and Anthrax (Diptera, Bombyliidae; 23.3
%). Nesting activity was greater during the receding water phase, which coincides with the period of less
precipitation. It is suggested that the seasonality of T. rogenhoferi is dependent on prey availability, which
in turn is influenced by the flood cycle.