Studies into the ecological energetics of the wireworm melanotus rufipes hbst. (goleoptera : elateridae)

Abstract

The study was an investigation into the ecological energetics of the Elaterid, Melanotus rufipes Hbst. Prior to this study little was known of the biology and ecology of this animal, therefore such data were presented as background material for the bioenergetic study. Analyses of the head-width frequency distribution in relation to instar number revealed that male animals pass through fourteen instars and female animals through fifteen instars. The duration of the life cycle was found to be seven years in male and eight years in female animals, the adult stage lasting only one year. The population ecology of M. rufipes was investigated using random and "whole log" sampling techniques. The data were expressed as the annual change in numbers and biomass. To determine energy flow through a population of M. rufipes it was necessary to solve the bioenergetlc equations:- C = A + F 1. A = R + Pg + Pr + U 2. C = energy consumed A = energy assimilated F = energy egested R = energy respired Pg = energy of growth Pr = energy of reproduction U = energy of excretion (not measured) Preliminary feeding studies utilising simple food preference tests and flame photometry techniques revealed that M. rufipes larvae have a carnivorous preference. Further feeding studies culminated in the calculation of ingestion, assimilation and faeces production rates. No evidence could be found for feeding in the adult stage. A continuously recording electrolytic respirometer and Varburg apparatus were used to measure respiratory rates. This enabled the annual respiratory metabolism of larval and adult animals, to be calculated. Monthly values of oxygen consumption per unit weight of animal produced characteristic L-shaped curves. Data were presented on the respiratory loss of each instar per unit time. Further respiratory investigations were made into the effect of size upon metabolism, the effect of feeding on the respiratory rate and the release of CO(_2) from the spiracies of H. rufipes. Additional data suggested that temperature acclimatization is not manifest as a change in respiratory rate. Growth rates were calculated from laboratory and field data and expressed in the form of a growth curve. The calorific values of whole animals, eggs, faeces and food were determined using a Phillipson microbomb calorimeter. This enabled calorific equivalents to be calculated for all parameters of the bioenergetic equations and individual energy budgets were thus prescribed for each instar and the adult stage of M. rufipes. From these data a mean energy budget ("best estimate") was calculated thus: Mean ingestion (C):-19»55 k. cals/l00 L. timber/year, assimilation (A):- 17.48 k. cals/l00 L. timber/year, egestion (F):- 1.86 k. cals/l00 L. timber/year respiration (R):- 2.74 k. cals/l00 L.timber/year and growth (Pg):-4.15 k. cals/100 L. timber/year. The assimilation percentage on a calorific basis was 90.3% (cf. 86.3% by weight). The ratio of secondary production/respiration was 28.6%.