Losses of Cd, Hg, and Zn During Metamorphosis in the Beetle Tenebrio Molitor (Coleoptera: Tenebrionidae)

Abstract

Insects occur in great numbers and are important for the transport of metals between trophic levels in food webs. Therefore, processes influencing metal concentrations in insects are important for the distribution of metals in ecosystems. The metamorphosis in holometabolous insects is of importance for metal concentrations. During this process some organs undergo an extensive breakdown as new organs are built up (Wigglesworth 1974). In the course of this process, concentrations of Cd were found to be altered .The impact of the metamorphosis on concentrations of other metals has been less studied. Nuorteva and Nuorteva (1982) found that Hg concentrations were lower in adult blowflies than in larvae, which suggests that Hg concentrations are altered during metamorphosis. Zn is an essential metal and is subject to homeostatic regulation (Chapman 1982). If no changes in metabolic pathways are needed, the optimal concentration of Zn may remain unchanged.The aim of this study was to measure the loss of Cd during metamorphosis in an insect and to determine whether Hg and Zn undergo a similar type of decrease. Hg was studied in both inorganic and methylated forms in order to reveal how the chemical form of this metal influences its metabolism. Tenebrio molitor was used in this study because adults and larvae share the same diet. Since this study lasts from the larval stage to the adult stage, the type of food is not changed. A shift in diet could influence the metabolism of the metals. MATERIALS AND METHODSThe metals were accumulated during the larval period in Tenebrio molitor. Preultimate instar larvae of T. molitor were kept in darkness at 20°C and 65% R.H.For each treatment, 10 larvae were reared individually in glass boxes and given wheat bran as food. The larvae were also given a piece of potato containing 109 Cd, 203 Hg, Methyl-203 Hg or 65 Zn. The potato pieces, approximately 2*5*10 mm, had been incubated 30 min in a 0.9% NaCl solution containing one of the metals. After the incubation, the potato pieces were dried on a paper towel for 1 hr and thereafter given to the larvae. The potato pieces were replaced by untreated potato after one week.Correspondence to: L. LindqvistThe following chemicals were used: 109 C d C l 2 , specific activity 1.76 mCi/mg, 65 ZnC1 2 , 1.62 mCi/mg, 203 Hg(NO 3 ) 2 , 1.37 mCi/mg; all of which were purchased from Du Pont Scandinavia, Stockholm, Sweden. Methyl-203 Hg was synthesized according to Naganuma et al. (1985).Metal contents were measured in the larvae in vivo during the last larval stage using a gamma-counter (Searle model 1185). Thereafter contents of the metals were monitored every third day throughout metamorphosis and for 27 days following eclosion of adults. RESULTS AND DISCUSSIONContents of all the studied metals declined at pupation when the exuvium was cast off and the pupal stage began. The 109 Cd content of newly eclosed adults was 76% of that of the last instar larvae. For 65 Zn it was 87%, for 203 Hg 65% and for methyl-203 Hg 83% (Fig. 1).In various insect larvae Cd ...

Elemental Concentration in Mealworm Beetle (Tenebrio molitor L.) During Metamorphosis

“…However, our results also demonstrated that in the pupae and second generation adult, Zn concentration was higher than in the second generation adult, so Zn concentration may have a role in the metamorphosis. Similar to our study, Lindqvist and Block [2] also demonstrated that during Fig. 2 Rank correlation between elemental concentration of food and studied larvae stages.…”

“…c Third larvae stage metamorphosis, remarkable difference may be in elemental concentration among developmental stages. A study of Polydesmida species also found differences in Ca, Mg, K, Na, Zn and Cu concentration between larvae and adult [2].…”

“…This difference may caused by an iron company which was near their sampling site [30]. Lindqvist and Block [2] demonstrated the Zn concentration was not affected by metamorphosis. In contrast with their findings, our study indicated that the Zn concentration was higher in the first larvae stage than in pupae.…”

“…An earlier study also demonstrated that the K and Zn had effect on the growth of larvae [6]. However, the metamorphosis plays an important role in the metal accumulation in holometabolous insects, which is particularly important in environmental studies [2].…”

“…They are good indicators because of their high diversity and they have an important functional role in the terrestrial ecosystem [1]. Among terrestrial invertebrates, insects play an important role in elemental transport chains [2]. Insect populations are sensitive to their habitat quality and they can indicate the changing of their habitats with their quantitative and qualitative parameters.…”