invertebrates

We report on our research efforts towards developing efficient equipment for the automatic recognition of insects using only the acoustic modality. Specifically, we deal with three groups of insects, namely the crickets, cicadas and katydids. Inspired by well-documented tactics of speech processing, the signal processing employed in the present work is elaborated further with respect to the sound production mechanisms of insects. In order to improve the practical efficacy of our equipment, we adopt a score-level fusion of classifiers with non-parametric (probabilistic neural network) and parametric (Gaussian mixture models) estimation of the probability density function. An efficient hierarchic classification scheme is introduced, where the identification of unlabelled input takes place at various levels of hierarchy, such as suborder, family, subfamily, genus and species. We evaluate the practical significance of our approach on a large and well-documented catalogue of recordings of crickets, cicadas and katydids. For the hierarchic classification scheme, we report identification accuracy that exceeds 99% at suborder and family levels. In the straight classification scheme, we report accuracy of 90% for 307 species.

This study provides the first description of the call structures of twenty ensiferan species constituting the nocturnal acoustic community of an evergreen forest in Southern India. Of the twenty species, ten belonged to the superfamily Grylloidea, nine to the superfamily Tettigonioidea and one to the superfamily Gryllacridoidea. The calls of the gryllid species were narrow-band with dominant frequencies ranging from 3 – 7 kiloHertz. The calls of the tettigoniids covered a wide spectral range, reaching far into the ultrasound in some species. Four of the nine tettigoniid species had narrow-band, relatively low frequency calls centred at 3, 9, 11 and 15 kiloHertz respectively. The temporal patterns of the species were diverse, with syllable durations ranging from eight to 63 milliseconds and syllable periods from 17 milliseconds to two seconds. The calls of the species showed considerable overlap in both spectral and temporal features. Calling activity peaked between six o’clock in the evening and midnight and died down subsequently. We found no diel partitioning of calling time between acoustically communicating ensiferan species. Species accumulation curves suggest that the acoustic community has been almost completely sampled.

We present the first description of the calls and stridulatory structures of males and females of an Indian weta species from the Western Ghats of Southern India. Calls of males and females produced by femoro-abdominal stridulation were recorded and call features such as chirp duration, chirp period, syllable period and syllable duration were characterised. The calls of males were highly stereotyped with regular chirp periods and durations whereas chirp rates in the female calls were more variable. The number of syllables per chirp was constant for males and females and the fine temporal features such as syllable periods and syllable durations showed low inter-individual variation in both males and females. The arrangement of femoral stridulatory structures was different from the previously described anostostomatid species. The high stereotypy of calls of males and females indicates that the signal could serve for identification of species and sex

Five distinct song types of the genus Mecopoda were found in Southern India. Four were morphologically indistinguishable. Some of them were both sympatric and had synchronous breeding seasons. The songs of these five song types ranged from simple short chirps to highly complex songs with multiple components. The temporal patterns of the songs of the five song types were very distinctive, whereas their spectral features were similar. Component elements of the different songs were distinct despite overall similarity. The song types possibly represent sibling species.

Exploitation of seed hardness, as a mechanism of host plant resistance, could be a useful component of the integrated control of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae). However, traditional methods of measuring larval development period using bioassays do not provide any information on larval feeding activity within seeds. To overcome this difficulty, a biomonitor was used to investigate feeding in seeds of Vigna spp. of different hardness. Larval weight and activity counts were lower in the hard seeded types. Larvae feeding in soft seeds increased their activity with each stadium, with each stadium separated by periods of inactivity. Conversely, for larvae in hard seeds, activity in the second stadium was prolonged and almost indistinguishable from the third and fourth stadia. It is suggested that associations between seed hardness and bruchid development be investigated as contributors to a better understanding of the mechanisms of host plant resistance.