Native insects can become epidemic pests in agro-ecosystems. A population genetics approach was applied to analyze the emergence and spread of outbreak populations of native insect species. Outbreaks of the mirid bug, Stenotus rubrovittatus, have rapidly expanded over Japan within the last two decades. To characterize the outbreak dynamics of this species, the genetic structure of local populations was assessed using polymorphisms of the mtDNA COI gene and six microsatellite loci. Results of the population genetic analysis suggested that S. rubrovittatus populations throughout Japan were genetically isolated by geographic distance and separated into three genetic clusters occupying spatially segregated regions. Phylogeographic analysis indicated that the genetic structure of S. rubrovittatus reflected post-glacial colonization. Early outbreaks of S. rubrovittatus in the 1980s occurred independently of genetically isolated populations. The genetic structure of the populations did not fit the pattern of an outbreak expansion, and therefore the data did not support the hypothesis that extensive outbreaks were caused by the dispersal of specific pestiferous populations. Rather, the historical genetic structure prior to the outbreaks was maintained throughout the increase in abundance of the mirid bug. Our study indicated that changes in the agro-environment induced multiple outbreaks of native pest populations. This implies that, given suitable environmental conditions, local populations may have the potential to outbreak even without invasion of populations from other environmentally degraded areas.
Sound trappin.cr of male mosquitoes in the field svas impros'ed ",ith the introduction of an artificial swarm marker. A 1 × 2.5 m black cloth was wrapped around the base of a O.7-m high tripod, and two or four sound traps were hunsr above the cloth at O.7 and 1.5m, During dusk, 370Hz sound at 100dB was emitted for 5-sec duration and at 15-sec intervals by each speaker to trap Culex tarsalis and Culex tritaeniorh},nchus. The sound-trapped mosquitoes were mostly 3and 4-day-old males. The standard deviation of their age was much smaller than that of the resting males. Two weeks of removal sampling of Cx. tarsalis males by 3 or 6 sets of 12 sound traps from a stand of marsh fleabane in California may have reduced the insemination rate of the unfed resting female population from 22f.i・ to zero, while the insemination rate remained unchanged at 55% in a comparison area.
A series of experiments were conducted to develop a meridic diet for adults of the West Indian sweetpotato weevil, Euscepes postfasciatus, by modifing the diet for larvae of E. postfasciatus developed by Shimoji and Kohama (1996b). Adult weevils were reared at 26°C, 70% RH, under 14L10D photoperiodic conditions. Within the range of KOH doses tested (0-0.107 mol/l), as the KOH dose was increased in the diet, hatchability of the eggs laid increased and longevity of females decreased. The pH of water in the diet did not affect longevity, fecundity and hatchability, even though the diet containing acid water (pH 2.7) resulted in a higher number of hatched offspring than the other diets containing distilled water (pH 6.0), mineral water (pH 9.0) and alkaline water (pH 11.1). Constituents of the tentatively developed diet were 50 g sweetpotato powder, 20 g agar, 20 g sucrose, 12 g casein, 10 g powdered cellulose, 5 g yeast extract, 2.5 g Vanderzant vitamine mixture, 1.5 g Wesson's salts, 2.99 g KOH, 1 g sorbic acid, 1 g methyl paraben, 0.4 g cholesterol, 0.2 g chloramphenicol, and 500 ml acid water.
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