Are Aristolochic Acids Responsible for the Chemical Defence of Aposematic Larvae of Battus polydamas (L.) (Lepidoptera: Papilionidae)?

Aristolochic acids (AAs) are thought to be responsible for the chemical protection of the aposematic larvae Battus polydamas (L.) (Papilionidae: Troidini) against predators. These compounds are sequestered by larvae from their Aristolochia (Aristolochiaceae) host plants. Studying the role of the chemical protection of the second and fifth instars of B. polydamas against potential predators, we found that the consumption of larvae by the carpenter ant Camponotus crassus Mayr and young chicks Gallus gallus domesticus was dependent on larval developmental stage. Second instars were more preyed upon than fifth instars; however, the assassin bug Montina confusa Stål was not deterred by chemical defences of the fifth instar B. polydamas. Laboratory bioassays with carpenter ants and young chicks using palatable baits topically treated with a pure commercial mixture of AAs I and AAs II in concentrations up to 100 times those previously found in B. polydamas larvae showed no activity. Similar results were found in field bioassays, where palatable baits treated as above were exposed to the guild of predators that attack B. polydamas larvae and were also consumed irrespective of the commercial AA concentration used. These results suggest that the mixture of AAs I and AAs II have no defensive role against predators, at least against those investigated in the present work. Other compounds present in Aristolochia host plants such as O-glycosylated AAs; benzylisoquinoline alkaloids; and mono-, sesqui-, di-, and triterpenes, which can be sequestered by Troidini, could act as deterrents against predators.

Nanoscale radiofrequency impedance sensors with unconditionally stable tuning.

Impedance sensors perform an important role in a number of biosensing applications, including particle counting, sizing, and velocimetry. Detection of nanoparticles, or changes in, e.g., the interfacial Debye-Hückel layer, can also be performed using nanoscale impedance sensors. One method for monitoring changes in the local impedance is to use radiofrequency reflectometry, which when combined with an impedance-matched sensor can afford very high sensitivity with very large detection bandwidth. Maintaining sensitivity and dynamic range, however, requires continuous tuning of the impedance matching network. Here we demonstrate a dual feedback tuning circuit, which allows us to maintain near-perfect impedance matching, even in the presence of long-term drifts in sensor impedance. We apply this tuning technique to a nanoscale interdigitated impedance sensor, designed to allow the direct detection of nanoparticles or real-time monitoring of molecular surface binding. We demonstrate optimal performance of the nanoscale sensor and tuned impedance network both when modulating the concentration of saline to which the sensor is exposed and when electronically switching between sensors configured in a two-element differential array, achieving a stabilization response time of <20 ms.