Effect of feces from pine-fed larvae of Dendrolimus pini L. (Lep., Lasiocampidae) on the germination and development of pine, birch and oak seeds

Germination and growth of Pinus sylvestris L., Betula pendula Roth. and Que rcus robur L. were investigated under laboratory conditions. Sterilized san d was used as the substrate and supplied with (a) increasing amounts of fae ces of larvae of Dendrolimus pini L. which had been reared previously on Sc otch pine and (b) a solution of NH4NO3 of the same N-concentration as the f aeces. The germination of pine and birch decreased strongly with increasing amounts of faeces, whereas the germination of oak was unaffected. When the inhibition of germination was overcome the further growth proceeded accord ing to the species-specific growth pattern during a period of 200 days (oak ) and 300 days, respectively (pine, birch). It was influenced neither by th e supply of faeces nor of fertilizer. It is concluded from the results that the faeces of phytophagous insects contain inhibitory components which bec ome effective only during the germination process of the species if there i s a poor supply of nutrients in the seed (pine, birch). The subsequent stag e of germ growth however, is not affected. The results are discussed in ter ms of a possible ecological function for insects as regulators of the speci es composition following mass propagations.