Increased reproduction by pea aphids in the presence of secondary parasitoids

1. The influence of the presence of secondary parasitoids on aphid reproduc tion was tested in a field experiment. 2. Single pea aphids Acyrthosiphon pisum in clip cages on potted bean plant s were exposed to a collection of secondary parasitoids enclosed within a s mall perforated bag. The aphids were exposed to volatile chemicals released by the secondary parasitoids but there was no physical contact. 3. The production of nymphs was recorded over an 11-day period. Aphids prod uced significantly more offspring in the presence of secondary parasitoids than in the absence of secondary parasitoids (36.9 vs. 31.2). 4. This is the second reported occurrence of this phenomenon, and the reaso ns for its occurrence and its consequences for aphid population and communi ty ecology are discussed.