Energy and nitrogen budgets for larval and aduit Paropsis charybdis Stål (Coleoptera: Chrysomelidae) feeding on Eucalyptus viminalis.

Abstract

| (1) Paropsis charybdis, the Eucalyptus tortoise beetle, is a serious defoliator of several Eucalyptus species in New Zealand. A series of laboratory experiments demonstrated the growth characteristics of larvae and adults when feeding on E. viminalis at 20°C. These were used as the data bases for quantifying its trophic relationships in terms of dry matter, energy and nitrogen. (2) The four larval stages lasted 4.0, 2.5, 3.0 and 9.5 days. Growth was exponential until the second day of the fourth instar, when the superficially inactive prepupal stage began. The pupal stage lasted 9.5 days. Female beetles started to lay eggs 15 days (av.) after eclosion. (3) Larvae attained a mean maximum dry weight (dwt) of 53.29 mg. Reproductive females weighed 63.40 mg, and males 46.71 mg. (4) The guts and their contents contributed up to 50% of total larval dry weight and 15% of adult dry weight. (5) Studies of the trophic relationships of P. charybdis larvae were based upon budgets whereby consumption (C) equals the sum of production (P), respiretion (R) and egesta (FU). Production was divided into gut-free larval production (P L* ) and exuvia (P EX)+R+FUin J: 3,561.5 = (491.3+43.4) + 284.5 +2,574.9 in mgN: 4.001 = (2.078 + 0.200) +1.657 (no R term) . P = P L* + P EX The derived R term (R c), calculated as: R c = C - FU - (P = P L* + P EX) = 34.84 (6) Daily budgets of an average adult, where ΔP AD reflects the change in body weight and P R=reproductive production, were: C =(ΔP AD + P R) + R +FU in mg dwt: 27.36 = (ΔP +2.25) +R + 14.53 in J: 591.1 = ΔP + 65.4) + 82.0 +362.6 in mgN: 0368 = (ΔP AD + 0.252) + 0.285. The budget assumes that male P R is zero and includes a corrected R term whereby R C=1.43 R M. ΔP AD can be assumed to equal zero over a long term, although fluctuations were apparent during the experimental period. (7) The amount of leaf material removed but not eaten by larvae (NU) was 22.6 mg, 462.4 J or 0.526 mgN. Thus, the total material removed (MR = C +NU) was 194.3 mg, 3978.9 J or 4.527 mgN. NU per day for an average adult was 4.86 mg, 99.5 J or 0.113 mgN. Therefore adults removed 32.33 mg, 659.9 J or 0.751 mgN per day. (8) Ecological efficiencies (energy) of P. charybdis larvae (using P = P L* + P EX and A = assimilation + C - FU ) were: net ecological efficiency (P.A.-1)=56.8%, gross ecological efficiency (P.C-1)=15.2%, assimilation efficiency (A.C.-1)=26.8%, P.R.-1=121.5%. Adult efficiencies were: P. A.-1=28.6%, P.C.-1=11.1%, A.C.-1=38.7% and P.R.-1=55.7%. Efficiencies in terms of nitrogen were (larval data followed by adult data in parentheses): P.A.-1=97.2 (71.4)%, P.C.-1=56.9 (39.5)% and A.C.-1=58.6 (55.3)%. (9) Regressions were calculated to link larval length (1) or larval live weight (lwt) and the dry weight of leaf material removed from a tree by that individual so that these results can be readily applied to field studies: logMR = -2.042 + 3.418 log1 logMR = -0.728 + 1.023 log 1wt.