Results of treatments with natural insecticidal substances on the development and physiological state of insects
Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences,64 Kreutzwaldi St., 51014 Tartu, Estonia; e-mail: email@example.com
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.