Utilization of dry matter and bioelements in larvae of Neodiprion sertifer Geoffr. (Hym., Diprionidae) feeding on Scots pine (Pinus sylvestris L.).

In the laboratory the consumption (C), egestion (F), assimilation (A) and assimilation efficiency (A/C) of dry matter and of the bioelements C, N, P, K, Ca, Mg, S and Na were studied weekly during the whole feeding stage. The larvae were reared in clusters of 10 individuals (on average 3.5 ♂♂ and 6.5 ♀♀), fed one-year-old needles. The average values of (C), (F) and (A) were 2,950, 2,530 and 414 mg dw per cluster, respectively, implying a dry matter assimilation efficiency of only 14.0%. The mean production of tissue (P) per cluster amounted to 250 mg dw. The concentration of bioelements in faeces (in order as above) was 51.2, 0.80, 0.08, 0.36, 0.41, 0.11, 0.10 and 0.02% of dw, and in larval tissue 57.5, 7.60, 0.64, 0.85, 0.24, 0.22, 0.24 and 0.06% of dw, respectively. The concentration of N and P in larval tissue was 5.8 and 4.9 times higher than in food, that of K, Mg, S and Na about twice, that of C and Ca about equal or less. The assimilation efficiency of the bioelements was estimated at 14.5, 59.3, 47.4, 20.9, 4.6, 12.5, 13.8 and 44.4%, and the energetics (C), (F), (A), (P) and (R=A-P) at 61,900, 53,600, 8,320, 6,710 and 1,610 J per cluster, respectively. It is argued that in N. sertifer the high consumption rate, low efficiency of dry matter assimilation and low nitrogen accumulation, in all attained at a low maintenance cost, are adaptations to a food low in nitrogen content (1.3% of dw). The study is part of an investigation on the interaction between insect consumption and pine growth, performed within the Swedish Coniferous Forest Project.