FURTHER STUDIES OF OLFACTION IN LARIOPHAGUS DISTINGUENDUS FÖRST. (HYM., PTEROMALIDAE)

by

AHMED H. KASCHEF (Entomology Department, Faculty of Science, Ain Shams University, Cairo (Abbassieh) ) (With 4 Figures) (Rec. 8-111-1963)

INTRODUCTION HASE (1924) pointed out that the Chalcid parasite Lariophagus disting- uendus F6rst. seems to thrive better in cultures of the bread Stego- bium paniceun2 L. than in cultures of the wheat Calandra granaria L. A detailed account of the behaviour of L. d.istinguendus F6rst. was given by the author (1959) and it has been shown that the female of this parasite finds its host mainly by the sense of smell which resides entirely in the antennae. More recently, KASCHEF (1959 & ig6i ) showed that L. disting- uendus could be reared from two new hosts, Rhizopertha dominica Fab. and Gibbiuni psylloides Czemp. It seemed, therefore, worthwhile to investi- gate the oviposition responses of this parasite to the odour of the following five hosts: Calandra granaria L., C. oryzae L., Stegobium pauiceuvr2 L., Rhizopertha dominica Fab. and psylloides Czemp.

MATERIAL AND METHODS All the experiments were carried out in a dark room with a light inten- sity of i5 lux, and having an average temperature of 23° C. and relative humidity of 45%. The to be tested were taken from the feeding jars immediately before the experiment. The duration of each test was usually one hour after which the was replaced in its original culture. The apparatus used (Fig. i ) is in form of a wooden chamber 22 X 7 X 4.5 cm. The base is relatively thick and has seven holes each of 2.5 cm. height and 1.5 cm. diameter placed at equal distances from one another. In these holes are fitted seven small cups made of plastic and full of semolina (a powdered cereal) up to 5 mm. below the edge. A perforated zinc plate which had 27 meshes per inch, covered with muslin, was placed 32 above the cups. The whole apparatus was covered from above by a glass plate which allowed observation of the behaviour of the parasite inside the chamber.

Fig. i. Apparatus used; A, Longitudinal section; B, Cross section; g, glass plate; z, perforated zinc plate covered with muslin; i to 7, plastic cups containing semolina. The host was placed in cup No. 4 and the female of the parasite was released on the metal plate through the right end of the wooden chamber. Its behaviour was observed and its position in the chamber noted every half minute. The insect would walk through the chamber from one end to the other stopping for periods of varying length above the cup containing the attractive group. The behaviour was noted in the following manner: the reaction chamber was considered to be divided into seven equal zones corresponding to the seven cups and numbered I to 7. The power of attraction was estimated by recording the duration of stopping and investigation which the parasite showed above the attractive group. In order to test the significance of the difference between the results obtained Student's t was calculated, using the equation t = (Xl - X2) J - SX1 X2, and then the probability P was estimated.

RESULTS A. Preliminary experiments s with the empty appa- ratus. In order to be sure of the isotropism of the apparatus, a series of 30 experiments were carried out using thirty egg-laying females of Lario-