Tritrophic Interactions of Cowpea [Vigna unguiculata subsp unguiculata(L.)], Aphids [Aphis craccivora (Koch)] and Coccinellids [Menochilus sexmaculatus (Fab.)] under eCO2 and eTemp

Abstract

Experiments were conducted to understand the direct and indirect effects of temperature and elevated CO2 (eCO2), on tritrophic interactions of cowpea (Vigna unguiculata subsp. unguiculata L.), legume aphid Aphis craccivora Koch and coccinellid predator Menochilus sexmaculatus Fab. Reduction of the leaf nitrogen (6%), amino acid (6%) and protein (7%) of cowpea foliage with increased carbon (13%) and C:N ratio (21%) at eCO2 over aCO2 indicated the dilution of biochemical constituents at first trophic level. Shortened development time, DT and increment of reproductive rate, RR at eCO2 over ambient CO2(aCO2)was significant with increase in temperature from 20 to 35 °C. Reduction of the mean degree day, DD requirement of both nymphal (75.79 ± 15.163) and adult stages (157.15 ± 67.04) at eCO2 over aCO2 and same was reflected in the summation DD for both the stages at eCO2 (232.96 ± 80.32)and aCO2 (247.07 ± 64.77) across six temperatures. The ‘rm’ and ‘Ro’ increased gradually with increase in temperature followed the non-linear trend and reached maximum values at 27 °C with shortened ‘T’ across 20 to 35 °C temperatures at eCO2 indicating the significant variation of growth and development at the second trophic level. Decreased grub duration (23%) with increased predation capacity (19%) of M. sexmaculatus on A. craccivora at eCO2 over ambient was noted, indicating the incidence of A. craccivora is likely to be higher with increased predation in the future climate change scenario.