Growth, energy and nitrogen budgets and efficiencies of the growing larvae of Megachile pacifica (Panzer) (Hymenoptera: Megachilidae).

The larvae of Megachile pacifica, the leafcutter bee, develop within a cell constructed of pieces of leaf by the adult female which also provides a plug of nectar and pollen, the sole source of nutrient for the larvae. In this study, eggs (1 per cell) hatched in 2-3 days and larvae were fully grown after a further 9 days at 28° C.The mean larval dry weight (dw) when fully grown (P L ) was 18.89 mg. Larvae ate 45.99 mg (dw) (C) of their food leaving 0.90 mg (dw) unconsumed. The faeces (FU) weighed an average of 5.62 mg (dw) and their cocoon weighed 2.68 mg (dw) (P E ). The components of their energy budget (C=(P L +P E )+R+FU) were C=1079.4 J, P L =569.1 J, P E =62.25 J, R (metabolic energy measured with a Gilson respirometer)=218.3 J and FU=134.4 J. R calculated by difference was 313.6 J.Full grown larvae contained 1.17 mg of nitrogen (N). They egested 0.19 mg N and incorporated 0.16 mg N in the cocoons. They ingested 1.51 mg N (measured) - the calculated consumption of nitrogen (by difference) was 1.52 mg.The ecological efficiencies showed that these larvae are among the most efficient invertebrate converters of energy and nitrogen yet recorded. The assimilation efficiencies (A·C -1 ) were 87.5% (energy), 87.2% (N), the net ecological efficiencies (P·A -1 ) were 66.8% (energy) and 100% (N) and the gross ecological efficiencies (P·C -1 ) were 58.5% (energy) and 87.6% (N). the production to respiration ratio (x100) was 201.5% using calculated R.