Abstract
ABSTRACT: The objective of this research was to determine the thermal requirements and develop life expectancy and fertility tables of Aphis craccivora (L.) in Vigna unguiculata (Walp.). The insects were kept in Petri dishes and fed V. unguiculata leaf discs (cultivar BRS-Tumucumaque) under five constant temperatures (18, 22, 25, 28 and 31ºC). Live and dead insects and stages of development; the onset and duration of the pre-reproductive, reproductive and post-reproductive periods; the number of nymphs per female; and the longevity of the adults were quantified daily. Based on these observations, fertility life expectancy tables were developed, and the thermal requirements of the cowpea black-aphid were determined. Increased temperature influenced all stages of insect development, as well as the pre-reproductive and post-reproductive periods and the total number of nymphs per female. The base temperature for development was 9.13ºC with thermal development constant of 99.0 GD. The highest net reproduction rate (Ro) was at 25ºC. At 28ºC, the greatest capacity to increase in number (rm) was observed, as well as the highest finite rate of increase (λ) and the shortest time to double in number (TD). The thermal range between 22 and 28ºC can be considered most favourable to the development of A. craccivora in V. unguiculata. Temperatures below 22 and above 28ºC affect the fertility and survival of cowpea black-aphids. Increased temperature induces reproduction and reduces the longevity and life expectancy of A. craccivora in cowpeas.
Highlights
Cowpea (Vigna unguiculata (L.) Walp.) is widely cultivated in northern and north-eastern Brazil and is traditionally planted by family farmers in small areas with low technology and low productivity
Aphids were collected from cowpea plants on the campus of the Universidade Federal of Piauí, Teresina, Piauí, Brazil, and transferred to plants susceptible to cowpea, kept in an air conditioned room (25oC), under a light bench consisting of eight T10 40 W daylight fluorescent lamps and eight 40 W incandescent lamps, with the aim of maintaining a predator-free population of aphids
After stabilization of the stock population, an assay was conducted under five constant temperatures in biochemical oxygen demand (BOD) chambers with temperature and photoperiod control
Summary
Cowpea (Vigna unguiculata (L.) Walp.) is widely cultivated in northern and north-eastern Brazil and is traditionally planted by family farmers in small areas with low technology and low productivity. The change in cowpea cultivation, from small (family farming) to large areas (modern agriculture), can lead to serious phytosanitary problems. According to SILVEIRA NETO et al (1976), the main factors that regulate insect abundance are the availability of food and climate factors, especially temperature, which influences behaviour and the speed of development. Temperature is able to accelerate the population increase of a species, which can result in surpassing the level of insect damage in a smaller space of time. Aphis craccivora (Koch, 1854) (Hemiptera: Aphididae) is one of the main phytosanitary problems encountered by cowpea producers in Africa, Asia and Latin America (SINGH; JACKAI, 1985; PETTERSSON et al, 1998)
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