Peter Belton

Effects of the essential oil constituent thymol and other neuroactive chemicals on flight motor activity and wing beat frequency in the blowfly Phaenicia sericata.

BACKGROUND The effects were evaluated of the plant terpenoid thymol and eight other neuroactive compounds on flight muscle impulses (FMIs) and wing beat frequency (WBF) of tethered blowflies (Phaenicia sericata Meig.). RESULTS The electrical activity of the dorsolongitudinal flight muscles was closely linked to the WBF of control insects. Topically applied thymol inhibited WBF within 15-30 min and reduced FMI frequency. Octopamine and chlordimeform caused a similar, early-onset bursting pattern that decreased in amplitude with time. Desmethylchlordimeform blocked wing beating within 60 min and generated a profile of continuous but lower-frequency FMIs. Fipronil suppressed wing beating and induced a pattern of continuous, variable-frequency spiking that diminished gradually over 6 h. Cypermethrin- and rotenone-treated flies had initial strong FMIs that declined with time. In flies injected with GABA, the FMIs were generally unidirectional and frequency was reduced, as was seen with thymol. CONCLUSIONS Thymol readily penetrates the cuticle and interferes with flight muscle and central nervous function in the blowfly. The similarity of the action of thymol and GABA suggests that this terpenoid acts centrally in blowflies by mimicking or facilitating GABA action.

Innervation and neural excitation of ventral muscle fibres of the larva of the waxmoth, Galleria mellonella

Abstract The ventral muscle fibres may be classified anatomically as oblique, segmental, and intersegmental. All have a very dense innervation on at least one surface. Synaptic areas were found in all sections examined under the electron microscope. The largest segmental fibre has, at a conservative estimate, at least 1000 synaptic areas. Terminating axons run beneath the muscle fibre basement membrane and tracheoblasts while still wrapped in glial cells. Sections of axons showing synapses are either entirely surrounded by muscle cytoplasm and an elaborate subsynaptic reticulum or perhaps are still in contact with glial cells over part of their surface. Apart from this, synaptic areas resemble those previously described in other insects. All fibres examined were innervated by one fast axon and the five segmental fibres used in locomotion are evidently a single motor unit supplied by the same axon. The electrical response to nerve stimulation is similar to that described previously in other lepidopterous larvae but slower than that recorded from muscle fibres of adults. The responses are graded and not propagated. This nerve-muscle preparation has advantages over most others described for electrophysiological study of herbivorous Lepidoptera.

Flight sounds of the females of some mosquitoes of Western Canada

Sounds of females of thirteen western Canadian species of mosquitoes were recorded on tape and analysed to identify the fundamental (wingbeat) frequency. This frequency (f in Hz) was approximately related to wing length (f in mm) by the equation f = 822 × I−0,725 Wingbeat frequencies of the species overlapped but each was distinct from at least five others and in three species, from nine others. Apart from frequency, the characteristics of the sounds were similar from species to species. Males of the largest and smallest species could, in theory, easily use sound to discriminate between their own species and others at the opposite end of the range of size. Observations of swarming and mating of sympatric species in the field are discussed.

Deterioration of axonal membranes induced by phenolic pro-oxidants: roles of superoxide radicals and hydrogen peroxide

The susceptibility of axons to oxidative free radicals generated by pro-oxidant neurotoxins and related compounds was tested by applying the reagents to the disheathed ventral nerve trunk of the crayfish. Electrophysiological characteristics of the axons, including spike amplitude and rise time, were recorded, using intracellular glass microelectrodes. L-Dopa, or L-dopa in the presence of copper-(bis)-histidine (Cu-his), did not change significantly the electrophysiological characteristics of the axon. A 20 mM concentration of 6-hydroxydopamine (6-OHDA), 20 mM 6-OHDA in an anaerobic environment, and 20 mM 6-OHDA with inactivated catalase-SOD accelerated the rate of decline of the spike amplitude with time to 5-8 times the control rate. Simultaneously, parallel increases in rise time and spike duration were observed, consistent with partial depolarization of the resting membrane presumably resulting from increased permeability. Catalase, superoxide dismutase (SOD), or a mixture of catalase and SOD all afforded partial protection, catalase having the least protective effect, and catalase + SOD the greatest. In contrast, 20 mM H2O2, 2 mM H2O2, or Cu-his alone did not significantly accelerate deterioration of the axon. Most of the damage results from the interaction of H2O2 with O-2, rather than from the direct action of either species. p-Hydroxyphenylpyruvate (pHPP) in the presence of Cu-his induced a similar accelerated deterioration of the axon to 4.2 times the control rate. Catalase plus SOD partially protected against this effect, but either enzyme alone was not significantly protective.

Evidence for short-range sonic communication in lymantriine moths

Sexual communication of nun moth, Lymantria monacha (L.), pink gypsy moth, Lymantria mathura Moore, and fumida tussock moth, Lymantria fumida Butler (all Lepidoptera: Noctuidae: Lymantriinae), is known to be mediated by pheromones. We now show that males are attracted by the sounds of conspecific females over short distances and that wing fanning male and female L. monacha, L. mathura and L. fumida produce species- and sex-specific wing beat and associated click sounds that could contribute to reproductive isolation. Evidence for short-range communication in these lymantriines includes (i) scanning electron micrographs revealing metathoracic tympanate ears, (ii) laser interferometry showing particular sensitivity of tympana tuned to frequency components of sound signals from conspecifics, and (iii) phonotaxis of male L. monacha and L. fumida to speakers playing back sound signals from conspecific females. We conclude that tympanate ears of these moths have evolved in response not only to bat predation, but also for short-range mate finding and possibly recognition.

The First Record of Aedes (Hulecoeteomyia) japonicus (Diptera: Culicidae) and Its Establishment in Western Canada.

Abstract The potential disease-carrying mosquito, Aedes japonicus (Theobald) (Diptera: Culicidae), was identified among larvae collected in suburban Vancouver, BC, in July 2014, and over 200 were found at the same site in February 2015 where it presumably had overwintered in the egg stage. In late May 2015, a female was captured taking a bloodmeal 13km east of the larval site. This population and those in the Washington and Oregon states are clearly disjunct from those in eastern North America, and their origin, probably from one or more different introductions from Asia, is discussed. Key characters of those in British Columbia are examined and match the description of subspecies japonicus, presumably like the others in North America.

Phylogeography of the coastal mosquito Aedes togoi across climatic zones: testing an anthropogenic dispersal hypothesis.

The coastal mosquito Aedes togoi occurs more or less continuously from subarctic to subtropic zones along the coasts of the Japanese islands and the East Asian mainland. It occurs also in tropical Southeast Asia and the North American Pacific coast, and the populations there are thought to have been introduced from Japan by ship. To test this hypothesis, the genetic divergence among geographic populations of A. togoi was studied using one mitochondrial and three nuclear gene sequences. We detected 71 mitochondrial haplotypes forming four lineages, with high nucleotide diversity around temperate Japan and declining towards peripheral ranges. The major lineage (L1) comprised 57 haplotypes from temperate and subarctic zones in Japan and Southeast Asia including southern China and Taiwan. Two other lineages were found from subtropical islands (L3) and a subarctic area (L4) of Japan. The Canadian population showed one unique haplotype (L2) diverged from the other lineages. In the combined nuclear gene tree, individuals with mitochondrial L4 haplotypes diverged from those with the other mitochondrial haplotypes L1—L3; although individuals with L1—L3 haplotypes showed shallow divergences in the nuclear gene sequences, individuals from Southeast Asia and Canada each formed a monophyletic group. Overall, the genetic composition of the Southeast Asian populations was closely related to that of temperate Japanese populations, suggesting recent gene flow between these regions. The Canadian population might have originated from anthropogenic introduction from somewhere in Asia, but the possibility that it could have spread across the Beringian land bridge cannot be ruled out.

Sounds of Insects in Flight

Insects in flight displace air in time with their wing beat and therefore by definition produce sounds. The sounds range from the inaudibly low frequencies of 5–8 Hz produced by saturniid moths with wings 10 cm long (Bienz-Isler 1968) to the almost impossibly high frequencies above 1000 Hz of small biting midges with wings 1 mm long (Sotavolta 1947). Frequency is correlated with wing length, but despite painstaking studies by Sotavolta and others, no simple relationship has emerged between frequency and size that applies to all insects.

Plant terpenoids: acute toxicities and effects on flight motor activity and wing beat frequency in the blow fly Phaenicia sericata.

ABSTRACT We evaluated the acute toxicities and the physiological effects of plant monoterpenoids (eugenol, pulegone, citronellal and &agr;-terpineol) and neuroactive insecticides (malathion, dieldrin and RH3421) on flight muscle impulses (FMI) and wing beat signals (WBS) of the blow fly (Phaenicia sericata). Topically-applied eugenol, pulegone, citronellal, and &agr;-terpineol produced neurotoxic symptoms, but were less toxic than malathion, dieldrin, or RH3421. Topical application of eugenol, pulegone, and citronellal reduced spike amplitude in one of the two banks of blow fly dorsolongitudinal flight muscles within 6–8 min, but with citronellal, the amplitude of FMIs reverted to a normal pattern within 1 hr. In contrast to pulegone and citronellal, where impulse frequency remained relatively constant, eugenol caused a gradual increase, then a decline in the frequency of spikes in each muscle bank. Wing beating was blocked permanently within 6–7 min of administering pulegone or citronellal and within 16 mins with eugenol. &agr;-Terpineol-treated blow flies could not beat their wings despite normal FMI patterns. The actions of these monoterpenoids on blow fly flight motor patterns are discussed and compared with those of dieldrin, malathion, RH3421, and a variety of other neuroactive substances we have previously investigated in this system. Eugenol, pulegone and citronellal readily penetrate blow fly cuticle and interfere with flight muscle and/or central nervous function. Although there were differences in the effects of these compounds, they mainly depressed flight-associated responses, and acted similarly to compounds that block sodium channels and facilitate GABA action.

Host antibodies in mosquito bloodmeals: a potential tool to detect and monitor infectious diseases in wildlife.

Abstract When a female mosquito bites, it carries away a blood sample containing specific antibodies that can provide a history of the immune responses of its vertebrate host. This research examines the limits and reliability of a technique to detect antibodies in blood-fed mosquitoes in the laboratory. Mosquitoes were fed on blood containing a specific antibody, and then they were assayed using an enzyme-linked immunosorbent assay to determine the limits of detection of antibody over time, at different temperatures and initial antibody concentrations. The antibody, at an initial concentration of 1 μg/ml, could be detected in mosquitoes for 24–48 h after feeding. Blind tests simulating the assay of feral mosquitoes were used to test the reliability of the method and detected positive mosquitoes with few false negatives and no false positives. Specific antibodies also could be detected in mosquitoes that had been air-dried or preserved in ethanol. This research indicates that, in theory, the collection and immunological assay of blood-fed mosquitoes could be developed to detect and monitor infectious disease in wildlife.