EUROPEAN JOURNAL OF ENTOMOLOGY

Eur. J. Entomol. 109 (4): 491-502, 2012 | DOI: 10.14411/eje.2012.062

Respiratory metabolism of the pea aphid, Acyrthosiphon pisum (Hemiptera: Aphididae)

Karel SLÁMA¹, Pavel JEDLIČKA^2,3

¹ Biological Center of Czech Academy of Sciences, Institute of Entomology, Drnovská 507, 161 00 Praha 6; e-mail: slama@entu.cas.cz

² Biological Center of Czech Academy of Sciences, Institute of Entomology, Branišovská 31, 370 05 České Budějovice, Czech Republic; e-mail: jedlicka@entu.cas.cz

³ Department of Entomology, National Taiwan University, Taipei 106, Taiwan

The respiratory metabolism of different polyphenic forms of the pea aphid, including wingless and winged asexual females (virginoparae), sexual females (oviparae) and winged or wingless adult males, was investigated using a micro-respirographic method. The records revealed sub-nanoliter amounts per min of O₂ consumption or CO₂ output. Respiratory metabolism of individuals was monitored for 3 to7 h after removal of the aphid from the food plant. Most of the recordings were for relatively large (3.5 mg), wingless asexual females (virginoparae). These aphids exhibited a continuous and very regular respiratory gas exchange (example: specimen of 3.5 mg body mass consumed 180 nl of O₂ per min; released simultaneously 300 nl CO₂ per min; = standard metabolic rate of 3085 µl O₂ / g / h; R.Q. = 1.66). This continuous pattern of respiration occurred only when the aphids were kept at relatively high humidity. By contrast, aphids of various seasonal forms exhibited discontinuous respiratory gas exchange when kept in relatively dry air (atmospheric, room conditions). These patterns can be briefly described as follows: (a) Short and rather small micro-cycles of CO₂ emission, manifested usually by the sudden expiration of 60-120 nl of CO₂ once every 5 min; (b) Larger bursts of 240-480 nl of CO₂ with a periodicity of one hour; (c) Enormously large, discontinuous bursts of 10-14 µl CO₂, duration 10-30 min, repeated with a periodicity of several hours. There was no constant pattern of diffusive CO₂ emission (DGC). The aphids exhibited a pattern of CO₂ release that was appropriate for the external conditions, such as temperature and humidity, and internal physiological conditions such as metabolic activity, availability of reserve substances (carbohydrate, lipid) and water. Certain stages (wingless virginoparae) exhaled volumes of CO₂ greatly in excess of their O₂ consumption (R.Q. over 1.5). Sudden exhalations of CO₂ from the body were a consequence of a bulk production and outflow of CO₂ and not due to the diffusion of CO₂ previously accumulated within the tracheal system. Due to their generally high metabolic activity (1142 to 6780 µl O₂ / g / h), aphid tissue and organs produced relatively large amounts of metabolically formed carbonic acid. The resulting respiratory acidaemia was moderated by outbursts of gaseous CO₂, liberated from liquid carbonate buffers by a regulatory mechanism based on enzymatic hydration and neutralization of carbonic acid by discontinuous formation of gaseous CO₂.

Keywords: Hemiptera, Aphididae, Acyrthosiphon pisum, O₂ consumption, CO₂ "bursts", discontinuous respiration, respiratory acidaemia, virginoparae, oviparae

Received: February 16, 2012; Revised: May 9, 2012; Accepted: May 9, 2012; Published: October 5, 2012  Show citation