Projections for the next years indicate that plants will face increasing water shortages that can cause declines in the abundance of some species (such as cereals) and may increase crop vulnerability to insect outbreak and attack.
At the same time, some Authors suggested that plant water stress can lead to an increased availability of small nitrogenous molecules for consumption by phytophagous insects, resulting in their greater reproduction and survival. Field observations indicated that periods of stress and recovery (due to differential water abundance) are more beneficial to the quality of aphid diet than constant stress. In a drought scenario, pulses of water availability within periods of water shortage might permit increases in stress-induced nitrogen without the plant wilting due to reduced leaf turgor and water content. The resulting maintenance of turgor pressure would allow aphids to continue feeding from the phloem.
Moreover, water stress is related in plants to a significant reduction in both photosynthesis and protein synthesis leaving spare amino acids (readily converted to essential amino acids by aphid gut symbionts), that lead to higher survival, higher rates of increase and enhanced fecundity with shorter development times in some aphids, such as the peach potato aphid Myzus persicae.
This scenario suggests therefore that in the next years we should face a reduced crop growth and production, coupled with increased amount of damage due to aphids…. but.. is it true? Can we test if this hypothesis is true or not?
In the recent paper, published in Entomologia Experimentalis et Applicata, K. L. S. Simpson,G. E. Jackson and J. Grace (University of Edinburgh) carefully investigated the response of aphids to plant water stress. Interestingly, they reported that all the measures of aphid population performance showed a significant negative impact of water stress with lower aphid numbers, fitness and fecundity. These data are in agreement with previous studies showing that water stress led to a reduced population size and reduced growth and development rates, whereas they are controversial in respect to data published with the aphid Sitobion avenae whose populations significantly increased under a severe water stress. Are we missing something? or considering that these experiments have been done with different species… can we have opposite responses of diverse aphids in drought plants?
A final result published by Simpson et al. is related to the effects of aphids on well-irrigated plants since in a scenario of future frequent drought it would be necessary for us to support plant growth with water. Accordingly to the published data, aphid-infested plants show increased production of abscisic acid, a compound that causes stomatal closure, which is typical in drought stressed plants. In addition, aphids may induce drought-like symptoms in well-watered aphid-infested plants, causing reduced stomatal conductance and relative water content, lower leaf water potential, lower chlorophyll levels and lower photosynthetic rates.
Under future drought scenarios, do you prefer reduced crop production and yield due to water stress or reduced crop production and yield of irrigated plants due to aphid-induced stress?
K. L. S. Simpson, G. E. Jackson, J. Grace (2012). The response of aphids to plant water stress – the case of Myzus persicae and Brassica oleracea var. capitata. Entomologia Experimentalis et Applicata