Thermal requirements and age-specific life tables of cowpea aphids in cowpea under natural field conditions

ABSTRACT: Thermal requirements and life tables of insects are important tools in the ecological management of pests. Thus, this study aimed to construct age-specific life tables for Aphis craccivora at different times of the year and, based on their thermal requirements, predict the occurrence of adults under field conditions. To that end, aphids of known age were kept in cages over cowpea plants at different times of the year - November 2016 and March, April, and June 2017 - at the Agricultural Sciences Center of the Federal University of Piauí. Parameters of development, fertility, and mortality were observed daily, allowing us to construct age-specific life tables, as well as an accumulated degree-day model to predict adult occurrence. The time of year affected the first and second stages of development of the cowpea aphid, the nymphal and reproductive periods, longevity, the biological cycle, the number of nymphs produced per female, the daily production of nymphs per female, life expectancy (ex), and survival (Lx). However, the fertility life tables showed significant differences only in the net reproduction rate (R0). The proposed degree-day model reached an accuracy of one day or more than the observed value, with a maximum error of 12.9%. We concluded that the proposed model is adequate to predict the occurrence of adults in the field and that the population parameters of A. craccivora in cowpea are negatively affected during November and positively affected in June

Thermal requirements, life expectancy and fertility tables of Aphis craccivora (Hemiptera: Aphididae) in Vigna unguiculata (Fabales: Fabaceae) under laboratory conditions

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