Characterization of sounds in maize produced by internally feeding insects: investigations to develop inexpensive devices for detection of Prostephanus truncatus (Coleoptera: Bostrichidae) and Sitophilus zeamais (Coleoptera: Curculionidae) in small-scale
Keywords:
acoustic probe, post-harvest, hidden infestation, grain, signal processing, TanzaniaAbstract
Infestations by Prostephanus truncatus Horn (Coleoptera: Bostrichidae) and Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) are prevalent in small-scale Zea mays L. storage facilities in Tanzania and other regions of sub-Saharan Africa. It is especially difficult to detect these species’ larvae, which feed unseen inside the grain kernels. An electronic device that acoustically detects and reliably indicates the presence of such larvae could assist pest managers in maintaining the quality of the stored maize. A study was conducted in a sound- and vibration-controlled environment to estimate the amplitudes and spectral ranges of signals that an inexpensive electronic system would encounter while detecting insects in maize storage facilities. Larva-infested wheat kernels from a laboratory colony of Sitophilus oryzae (L.), a species similar in size and behavior to S. zeamais, were placed in a pouch and inserted near the side or the bottom of a bag of maize. An acoustic probe was inserted into the bag, and recordings were made at multiple positions, 5–35 cm from the pouch. Numerous sounds of 4 different types were detected over a range of frequencies extending to 7 kHz, well within the signal-processing capabilities of currently available low-cost microcontroller platforms. Larval sound impulses were detected frequently within 25 cm from the pouch, but not at 35 cm. However, adjustable-length probes could be used to reach within 30 cm of all maize kernels in the types of containers commonly used in regional storage facilities. Thus, there is considerable potential to develop an inexpensive sensor/ microcontroller system useful for managing stored product insect pests in sub-Saharan Africa.
Resumen
Las infestaciones de Prostephanus truncatus Horn (Coleoptera: Bostrichidae) y Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) son frecuentes en instalaciones de pequeña escala de Zea mays L. almacenado en Tanzania y otras regiones del África subsahariana. Es especialmente difícil de detectar larvas de estas especies que se alimentan de manera invisible dentro de los granos de cereales. Un aparato electrónico que pueda detectar acústicamente y confiablemente la presencia de estas larvas podría ayudar a los profesionales den el manejo de plagas en el mantenimiento de la calidad del maíz almacenado. Se condujo un estudio en un ambiente de sonido y vibración controlada para calcular las amplitudes y rangos espectrales de las señales que un sistema electrónico de bajo costo podría encontrarse al detectar insectos en las instalaciones de almacenamiento de maíz. Granos de trigo infestados por una colonia de laboratorio de larvas de Sitophilus oryzae (L.), una especie similar en tamaño y comportamiento a S. zeamais, fueron colocados en una bolsa y puestos cerca del lado o de la parte inferior de una bolsa de maíz. Se insertó una sonda acústica en la bolsa y se realizaron grabaciones en múltiples posiciones, 5-35 cm de la bolsa. Se detectaron numerosos sonidos de 4 tipos diferentes en un rango de frecuencias que se extiende a 7 kHz, que estan dentro de las capacidades de procesamiento de señales de plataformas de microcontroladores de bajo costo disponibles actualmente. Se detectaron los impulsos de sonido de larvas con frecuencia dentro de 25 cm de la bolsa, pero no a los 35 cm. Sin embargo, se podrían utilizar las sondas de longitud ajustable para llegar dentro de los 30 cm de todos los granos de maíz en los tipos de recipientes utilizados comúnmente en las instalaciones de almacenamiento regionales. Por lo tanto, existe un gran potencial para desarrollar un sistema barato de sensor/microcontrolador útil para el manejo de plagas de insectos en productos almacenados en África subsahariana.
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