Diurnal feeding as a potential mechanism of osmoregulation in aphids

Abstract

Diurnal variation in phloem sap composition has a strong influence on aphid performance. The sugar-rich phloem sap serves as the sole diet for aphids and a suite of physiological mechanisms and behaviors allow them to tolerate the high osmotic stress. Here, we tested the hypothesis that night-time feeding by aphids is a behavior that takes advantage of the low sugar diet in the night to compensate for osmotic stress incurred while feeding on high sugar diet during the day. Using the electrical penetration graph (EPG) technique, we examined the effects of diurnal rhythm on feeding behaviors of bird cherry-oat aphid (Rhopalosiphum padi L.) on wheat. A strong diurnal rhythm in aphids as indicated by the presence of a cyclical pattern of expression in a core clock gene did not impact aphid feeding and similar feeding behaviors were observed during day and night. The major difference observed between day and night feeding was that aphids spent significantly longer time in phloem salivation during the night compared to the day. In contrast, aphid hydration was reduced at the end of the daytime feeding compared to end of the night-time feeding. Gene expression analysis of R. padi osmoregulatory genes indicated that sugar breakdown and water transport into the aphid gut was reduced at night. These data suggest that while diurnal variation occurs in phloem sap composition, aphids use night-time feeding to overcome the high osmotic stress incurred while feeding on sugar-rich phloem sap during the day.

Plant water stress intensity mediates aphid host choice and feeding behaviour

“…The boxplot displays the median as a horizontal line, the interquartile range as a box, the maximum and minimum values as bars or 'whiskers', and outliers are indicated with dots. Nachappa et al, 2016;Pineda et al, 2016), and the mechanisms commonly attributed are reduced turgor pressure and increased viscosity negatively affecting phloem access, ingestion rate, or osmoregulation.…”

“…On poorer quality hosts, aphids show an increase in the number of cell probes and the duration of salivation (Ponder et al, 2001), indicating difficulty in establishing sustained feeding sites. However, studies evaluating phloem feeding behaviour in response to water limitation have found mixed results, with some studies documenting a reduction in the time spent feeding from phloem on water-limited hosts (Guo et al, 2016) and some studies finding no difference in feeding (Ponder et al, 2001;Hale et al, 2003;Nachappa et al, 2016).…”

Expression of Thioredoxin/Thioredoxin Reductase System Genes in Aphid-Challenged Maize Seedlings

“…Aphid stylet passage, saliva excretion and food ingestion in the host tissues cannot be directly investigated, but these activities can be monitored with application of the electrical penetration graph (EPG) technique. This approach is widely used to assess the probing and ingestion behavior of the aphids [ 42 , 43 , 44 , 45 , 46 ]. Analysis of the several parameters derived from the EPG recordings (e.g., frequency, duration and sequence of different waveforms) enables in-depth assessment of behavioral responses of the aphids to the host plant tissues [ 23 , 24 ].…”

Variation Between Three Eragrostis tef Accessions in Defense Responses to Rhopalosiphum padi Aphid Infestation

“…However, we found no significant difference between RTC-406 and RTC-144 in the phloem phase. Aphids are phloem feeders that occasionally feed on xylem fluid (Nalam et al, 2020), possibly to attenuate the high osmotic potential of the phloem sap (Douglas, 2006;Tetreault et al, 2019). The EPG results expose that aphids spent more Gene expression patterns were sorted into up-and down-regulated genes upon 6, 24, and 96 h of aphid feeding on RTC-144 tef plants.…”