Cannibalism is a behavioral trait seen in a number of species and can be favored when the fitness gain outweighs the cost. In social wasps, field studies have suggested that food limitation causes larval cannibalism as a compensation of a meal for adult wasp and/or earlier production of the first workers, but experimental studies for the effect of food availability on larval cannibalism have been very scarce. Hence we examined whether Polistes chinensis antennalis foundresses exhibit a higher level of larval cannibalization under food-limited conditions than under food-available conditions. Larval cannibalization occurred frequently under both prey-and honey-limited conditions; however, young larvae were more frequently cannibalized than old larvae in the prey-limited colonies, while old larvae were more frequently cannibalized than young larvae in the honey-limited colonies. The number of days between colony initiation and the emergence of the first workers was not significantly different between the prey-limited and prey-available colonies, suggesting that under prey-limited conditions P. chinensis antennalis foundresses tend to cannibalize their young larvae and feed probably the flesh of these cannibalized larvae to old larvae in order to ensure the rapid production of the first workers. On the other hand, the number of days between colony initiation and the emergence of the first workers was longer in the honey-limited colonies than in the honey-available colonies. We propose explanations for the first time for why the foundresses in the honey-limited conditions cannibalized their old larvae more frequently than their young larvae in spite of this resulting in the delayed emergence of the first workers.

Periodical corrugations structured on a cylindrical conductor have cylindrical surface waves (CSWs), which are reflected at the corrugation ends and form a CSW-resonator. In this paper, intense radiations in terahertz region based on the CSW-resonator are reported. The CSWresonators with upper cut off frequencies in the modern IEEE G-band (110-300 GHz) are excited by a coaxially injected annular beam in a weakly relativistic region less than 100 kV. It is shown that there exists an oscillation starting energy for the CSW-resonator. Above the starting energy, very intense terahertz radiations on the order of kW are obtained. The operation frequencies in the range of 166-173 GHz and 182-200 GHz are obtained using two types of CSW-resonator with the different corrugation amplitude. Electromagnetic properties of the CSW-resonator can be controlled by the artificial structure and may play an important role in high-intensity terahertz generations and applications. V C 2015 AIP Publishing LLC. [http://dx.

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