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Neuropeptides are important with respect to almost all physiological processes and behavioural patterns in an organism. In the present study, muscle bioassays, immunohistochemistry and matrix-assisted laser desorption ionization timeof-flight (MALDI-TOF) mass spectrometry are used to investigate the distribution and efficacy of proctolin in the antennal heart of 36 species of lower Neoptera. In total, 20 species of Dictyoptera (cockroaches, termites, praying mantids), eight species of Saltatoria (crickets and grasshoppers) and eight species of Phasmatodea (stick insects) are investigated. The antennal heart of all tested Blattoidea, including the termite Mastotermes darwiniensis Froggatt, exhibit a strong proctolin-like immunoreactivity, as well as a high sensitivity to proctolin, whereas members of the second clade of cockroaches (Blaberoidea) are largely insensitive to proctolin and show only a weak proctolin-like immunoreactivity. The antennal heart of praying mantids (Mantodea) also contains only few proctolin-like immunoreactive fibres but is highly sensitive to proctolin. Such a high sensitivity is found also in Phasmatodea, although the antennal heart of these insects does not have proctolin-like immunoreactive fibres. These findings are supported by MALDI-TOF mass spectrometry; no trace of proctolin is detected in antennal heart preparations of Phasmatodea. In Saltatoria, only weak (or no) effects of proctolin are observed and, in most subtaxa, no proctolin-like immunoreactivity is visible in the antennal heart preparations. Only in Grylloidea is strong proctolin-like immunostaining found in processes of the antennal heart. In these species, weak or moderate effects of proctolin are observed in the antennal heart bioassay. In general, the differences in distribution of proctolin and effects on the antennal heart within the basal Neoptera cannot be deduced from their phylogenetic position, although they show conformity within each (sub)taxon.

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The action of the plant products quassin, cinnamaldehyde and azadirachtin was examined using pharmacological and electrophysiological methods. All three substances inhibited the beat rate of the antenna-heart, with quassin causing a diastolic and cinnamaldehyde a systolic block. Quassin delayed and azadirachtin at first accelerated the frequency of action potentials in the heart muscle, but 5 · 10 )3 m of the latter compound degraded the spike pattern and decreased the heart rate. A typical prolongation of the duration of the action potentials was observed. In recordings from a nerve of the frontal ganglion, quassin and cinnamaldehyde reduced the intervals between the spontaneous bursts, which turned into a continuous spike discharge with a decline in activity, while azadirachtin had no effect. Measurements in a single neurone of this ganglion revealed that quassin had a suppressive effect on the frequency and amplitude of the action potentials. These results suggest that the physiological effects demonstrated do not cause the primary insecticidal actions of these plant products.