Soybean plant response to the attack of Oberea brevis Swed. (Col., Cerambycidae)

In Madhya Pradesh, India, the girdle beetle, Oberea brevis Swed., attacked soybean plants on an average of 13.4% in 1969, 34.2% in 1973 and 21.1% in 1974. The attack in itself was responsible for the loss of 29.1% grains as compared to healthy plants. The larvae of both generations girdle the stems from inside to cut off a small portion of the stems for the protection of the diapausing larvae. By this the pod bearing portions of the plants fell down. It was noted that 52.5% of the infested plants were cut down at a mean height of 33 cm, and 21.9% plants at an average height of 6 cm at which the largest number of pods and grains were lost. Another significant cut‐off of 15.4% of the plants took place at an average height of 18 cm. A few plants were also cut near the top when the loss of pods and grains was comparatively small. The cut off height of the infested plants was negatively correlated with pod loss (r = –0.755), pod weight (r = –0.900), grain number (r = –0.955) and grain weight (r = –0.625) and a linear relationship was found between them. The weight of the grain from the top‐cut portions of infested plants was significantly reduced in relation to that of healthy plants and their germination capacity was also seriously affected. Zusammenfassung Wirkungen des Fraßes von Oberea brevis Szved. (Col., Cerambycidae) auf Sojabohnen In Madhya Pradesh, Indien, befiel der Ringelungs‐Bock, O. brevis , 1969 = 13,4%, 1973 = 34,2% und 1974 = 21,1% der Sojabohnen‐Pflanzen. Der Befall führte zum Verlust von i. M. 29,1% des Samengewichts, verglichen mit unbefallenen Pflanzen. Die Larven beider Generationen leben in den Stangen und ringeln diese von innen her, um Teile aus dem Stengel herauszuschneiden, die zum Schutz für die Larven‐Diapause verwendet werden. Hierdurch brechen die oberhalb der Ringelung befindlichen Pflanzenteile ab. Es zeigt sich, daß 52,5% der befallenen Pflanzen in einer Höhe von 33 cm, 21,9% in 6 cm Höhe und 15,4% in 18 cm Höhe abgeschnitten wurden, was zu einem nur geringen Verlust an Sojabohnen führte. Die Schnitthöhe war negativ korreliert mit der Zahl verlorengegangener Bohnen (r = –0,755), dem Verlust an Bohnengewicht (r = –0,900), der Verminderung der Samenzahl (r = –0,955) und dem Verlust an Samengewicht (r = –0,625). Zwischen diesen Gliedern bestanden lineare Beziehungen. Das Gewicht der Samen der an der Spitze abgeschiedenen Pflanzen war signifikant kleiner als jener von gesunden Pflanzen. Auch war ihre Keimfähigkeit verringert.