Destruction of Indoplanorbis exustus (Planorbidae) eggs by Pomacea bridgesi (Ampullariidae)

Abstract

Six size classes (5–9 mm, 10–14 mm, 15–19 mm, 20–24 mm, 25–30 mm and 30–34 mm) of the ampullariid snail Pomacea bridgesi were experimentally exposed to 10–25 egg capsules of the planorbid snail Indoplanorbis exustus. With one exception, in all the trials performed with the snails of the four highest size classes, egg capsules of I. exustus were destroyed by P. bridgesi, whereas in the 5–9 mm and 10–14 mm size classes, egg capsules were destroyed in 20% and 68.96% of trials respectively. An individual of Pomacea belonging to each of the six size classes could destroy, on average, 0.28, 2.27, 2.38, 3.82, 3.75 and 3.62 egg capsules, respectively, during a period of 24 hours. Irrespective of size class, an individual could consume 0–6 (average 1.57 0.08 s.e.) and damage 0–9 (average 1.14 0.10 s.e.) egg capsules per 24 hours. On average there are about 20 eggs in each capsule, so an individual of P. bridgesi would be able to destroy around 60 eggs of I. exustus daily. These observations are relevant to possible biological control of Indoplanorbis.