Energy and Nitrogen Relation for a Macrosiphum Liriodendri (Homoptera: Aphididae) Population in an East Tennessee Liriodendron Tulipifera Stand
1980
Van Hook, R. I. | Nielsen, M. G. | Shugart, Herman H. (Herman Henry)
Biomass and density of all instars of a Liriodendron aphid population on three mature trees in an east Tennessee yellow "poplar" stand were determined for the 1971 growing season. Concurrently, laboratory studies were carried out to ascertain rates of each aphid instar's metabolism, growth, reproduction, and honeydew production. Similarly, whole body caloric content and concentrations of N were determined for each instar. Results from these studies were utilized in estimating ingestion of sap by the aphid population, and in developing a mathematical model of aphid population dynamics. These estimates were used in preparing annual budgets of dry matter, energy, and N for the population. Maximum aphid biomass of 169 mg dry mass/m² ground area (Leaf Area Index = 4.7) occurred in early June coincident with maximum nitrogen concentrations in phloem sap and favorable canopy temperature. There was a second peak in population biomass in September, just prior to leaf abscission when nitrogen compounds were again mobile in the phloem streams. Reproduction and honeydew production were functions of temperature and followed a Q₁ ₀ = 2 relationship. Metabolism and growth were also functions of temperature but increased exponentially (Q₁ ₀ relationship) up to an optimum temperature, °22°C, and them declined rapidly. Values observed for these parameters were well within ranges reported in the literature for numerous aphid species. Energy budgets calculated for both laboratory and field populations of this aphid species indicate that M. liriodendri consumes ca. 400% of its dry body mass per day, or 185 kcal/m² annually. Of this ingestion, 65% goes into honeydew production (egestion), 6% into respiration, and 27% into production of biomass. Similar budgets prepared for nitrogen indicate that 970 mg N/m² are consumed annually, and of this, 27% goes into honeydew and 73% is incorporated into aphid biomass. Comparison of these data with standing pools of energy and nitrogen in the Liriodendron stand shows that this aphid population consumes 1% of annual photosynthate production and an amount equivalent to 17% of the annual standing crop of foliar N. The impact of this consumption on primary production is not presently known.
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