Results of treatments with natural insecticidal substances on the development and physiological state of insects

K. Jõgar, A. Kuusik, L. Metspalu, K. Hiiesaar, A. Luik and M. Grishakova

Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences,64 Kreutzwaldi St., 51014 Tartu, Estonia; e-mail: katrin.jogar@emu.ee

Abstract:

Reviewed are the results of treatments carried out in the Institute of Agricultural and Environmental Sciences of treatments with natural insecticidal substances on the development and physiological state of insects, using neurotoxical plant extracts (pyrethrins), plant extracts possessing several modes of action (neem) and an Insect Growth Regulator (extract of Ledum palustre possessing properties of juvenile hormone). Physiological changes evoked with treatments were monitored by means of complex methods including a constant volume respirometer, infrared actograph, infrared gas analyzer (IRGA),and a microcalorimeter.Diapausing lepidopterous pupae (Pieris brassicae, Mamestra brassicae) exhibiteddiscontinuous gas exchange cycles (DGCs). After treatments of the pupae of P. brassicae with neem, the DGCs were abolished, suggesting direct action on the neuromuscular system. The disappearance of DGCs was accompanied with lethal desiccation, supporting the hypothesis that DGC is an adaptation for restricting the respiratory water losses. Cyclic gas exchange was also lost after treatments with neem in adults of Leptinotarsa decemlineata. The clear gas exchange cycles in the pupae of Galleria mellonella, Tenebrio molitor and P. brassicae were also abolished after treatments with extracts of Artemisia vulgaris, Tanacetum vulgare, T. roseum and L. palustre. The timing of the normal and failed ecdysis (after treatment with L. palustre) as well as length of intercdysial periods in T. molitor pupae was measured exactly from calorimetric recordings. The treated pharate pupae transformed into extra-pupal instars, which is a symptom of juvenilizing effect.

Key words:

Physiology of diapause in pupae of Pieris brassicae L. (Lepidoptera: Pieridae)

K. Jõgar¹, L. Metspalu¹, K. Hiiesaar¹, A. Luik¹, A.-J. Martin¹, M. Mänd¹, R. Jaaniso² and A. Kuusik¹

¹Institute of Agricultural and Enviromental Sciences, Estonian Agricultural University, Kreutzwaldi 64, 51014 Tartu, Estonia; e-mail: katrinj@eau.ee
²Institute of Physics University of Tartu, Riia 142, 51014 Tartu, Estonia

Abstract:

Respiration patterns, water loss and heart activity were investigated during the first three months of diapause in non-acclimated pupae of Pieris brassicae. To observe and record diverse events during pupal diapause, a complex apparatus was used: a micro-calorimeter, an electrolytic respirometer, a fibre-optical oxygen sensor, a flow-through respirometer (infrared gas analyzer), an infra-red actograph and a thermocouple cardiograph. Most of the pupae (about 80%) reared in 2004 were characterised as long-cycle individuals whose discontinuous gas exchange cycles (DGCs) were very regular and lasted 26 hours on average. The remainder of the pupae studied were short-cycle individuals displaying irregular DGCs lasting less than 2 hours. Standard metabolic rates (SMR) measured during the first month of diapause between long- and short-cycle pupae did no differ significantly, being about 0.018 ml O₂ g^-1 h^-1. At the same time, water loss rate (WLR) in long- and short-cycle pupae differed significantly, being 1.07 and 1.61 mg g^-1 day^-1, respectively. During the first three months of diapause, the values of SMR and WLR did not change significally in the long-cycle pupae. In the short-cycle individuals, SMR and WLR thereupon increased gradually during the months, but the values of SMR never reached the levels characteristic of pharate adult development. The heartbeat reversal was characteristic for both the long- and short-cycle individuals but heart pauses in the first pupal group were regular, lasting 20–30 min, whereas in the second group the heart pauses were shorter and irregular.

From the results we concluded that the intensity of pupal diapause varied individually despite the apparently similar developmental conditions of the individuals, however, some hidden factors were obviously involved in diapause induction. The primary cause of the enhanced water loss in the short-cycle pupae was obviously the disturbing of the water conserving mechanisms due to the irregular gas exchange.

Key words:

(C)FV and (C)FO cycles, cold tolerance, discontinuous gas exchange cycles, heart activity, Pieris brassicae, pupal diapause, standard metabolic rate, water loss rate