In the United States, the pea aphid (Acyrthosiphon pisum, adult female and young shown here) has a broad host range and is a serious concern for commercial pulse producers, especially in the Pacific Northwest region. A new guide in the open-access Journal of Integrated Pest Management examines pea aphid biology and ecology, as well as various management practices. (Photo by Joseph Berger, Bugwood.org)

By Ramandeep Kaur Sandhi

Ramandeep Kaur Sandhi

Pulses are important legume crops grown all over the world. They provide a good source of plant proteins for human consumption and act as natural soil fertilizers with the capacity to fix atmospheric nitrogen. Pea aphid (Acyrthosiphon pisum), has a broad host range and can cause serious economic damage and yield losses in pulse crops such as fava bean, lupin, alfalfa, lentil, chickpea, grass pea, and field pea. In the United States, A. pisum is a serious concern for commercial pulse producers, especially in the Pacific Northwest region. In a new article published this month in the open-access Journal of Integrated Pest Management, Gadi V.P. Reddy, Ph.D., professor of entomology and insect ecology at Montana State University, and I examine the biology and ecology of A. pisum and review various management practices, including host plant resistance and cultural, genetic, biological, and chemical control.

Like other aphids, A. pisum removes sap directly from the leaves, stems, and pods, causing leaf curling and wilting. During feeding, it may transfer of over 30 plant viruses, including cucumber mosaic virus or beet yellows virus. As plants mature, A. pisum attacks flowers and pods. Excreted honeydew leads to sooty mold development, affecting photosynthesis.

Acyrthosiphon pisum has a complex life cycle with asexual and sexual reproduction. Asexual females developed from overwintering eggs in spring can be winged or unwinged in summer and can produce either winged or unwinged sexual males or sexual wingless females in the fall. Different facultative symbiotic bacteria and obligate intercellular bacteria provide benefits to pea aphid fitness, including better survival, tolerance to heat stress, resistance to parasitoid wasps, compensation for loss of essential symbionts, and induction of winged forms. Defensive strategies, including morphological, social, chemical, and behavioral traits used by pea aphids to avoid and escape predators, contribute to the success of this pest in the ecosystem.

Currently, there are no effective non-chemical methods available for pea aphid control, so most farmers growing pulses have relied on chemical insecticides. Various absolute and relative sampling methods, including sweep net sampling, are used for monitoring and determining economic threshold levels for this pest in different pulse crops. Although several studies from various regions of the world have identified resistant cultivars and varieties, mainly of pea, little information is available on the mechanisms (antibiosis, antixenosis, and tolerance) of resistance in these crops and cultivars at this time.

A severe infestation of pea aphid (Acyrthosiphon pisum) in fababeans can cause wilting (left) or leave plants podless by harvest (right). (Photos by Tyler Wist, Ph.D., originally published in Sandhi and Reddy 2020, Journal of Integrated Pest Management)

Our review of cultural methods to manage pea aphid (such as mixed cropping, intercropping, early seeding, mulching, and habitat manipulation) found that the results are mixed. Case studies showed that pulse crop monocultures, such as peas, attracted more aphids than fields intercropped with cereal or mustard crops. Some biological control agents, including aphid-eating lady beetles and parasitoids such as the wasps Aphidius ervi and A. smithi, regulated pea aphid populations below the economic injury threshold levels. Similarly, entomopathogenic fungi and bacteria proved effective against pea aphid, at least under laboratory conditions. The possibility of intraguild predation between different biological control agents (the potential for one predator to prey on another) needs to be considered and evaluated under field conditions.

Chemical insecticides, mainly Flonicamid and spirotetramat, have been registered for aphid control in different pulse crops in the U.S. and Canada. Because these chemicals carry the risk of negative effects on non-target organisms, emphasis is placed on the evaluation and use of plant secondary metabolites, plant-derived compounds, insect growth regulators, and botanical insecticides for effective pea aphid control. We include recommendations for future studies, such as expanding the number of known predators, parasitoids, and pathogen species available for pea aphid control, conserving natural enemies, and keeping insecticides as a last resort. This comprehensive review will be useful information to pea growers, stakeholders, and researchers working on pulse crops.

Ramandeep Kaur Sandhi got her B.S. and M.S. in entomology from Punjab Agricultural University in India and is currently a Ph.D. candidate at Montana State University. Email: ramansandhi2010@gmail.com.