CONRAD, Mont. – New insect pests may be coming into the Northern Plains in transportation shipments of pulses from all over the world.
A new insect pest, the Southern cowpea weevil, has been discovered inside shipment containers over the past four years.
“The Southern cowpea weevil is a storage pest, and a stored seed feeder, just like the pea weevil is,” said Dr. Gadi V.P. Reddy, entomologist at Western Triangle Agricultural Research Center. The pea weevil, found on Montana’s Hi-Line for the first time in 2014, has been found to be one of the most problematic pests in field peas.
The Southern cowpea weevil was found in a shipment of lentil seeds in 2015. Since then, the insect pest has been found in other shipment containers.
“The insect is mainly considered an economically important pest in lentils, cowpea, green gram and black grain worldwide,” Reddy said.
But the pest has a wide range of hosts. Other hosts include: peas, chickpea, pigeon pea, garden peas, mung beans, black-eyed peas, soybeans, lima beans, and wild legumes.
Since shipments come from all over the world, no one place is the probable source for the Southern cowpea weevil entering the state.
The insect has been a major problem in tropical climates, and is most common in the southern regions in the U.S. It has been distributed around the globe from such countries as Asia, Africa, Canada, South America, and Australia.
What happens inside the seed makes the seed non-viable.
When the seeds are stored in a very warm, humid place, the Southern cowpea weevil’s life cycle will be completed in about 20–23 days.
The female adults lay eggs on the seeds, gluing the eggs to the seed surface of host plants like lentils.
“Adults can lay as many as 90 eggs during their lifetime,” Reddy said.
The eggs will hatch in five or six days when the temperature is optimal at 90–95 degrees F. They begin burrowing deep into the seed through the seed base and begin feeding inside the seed.
“Temperature does play a major role in whether the eggs hatch or not,” he said.
The favorable temperature for the Southern cowpea weevil to complete all life stages ranges from 93 degrees F to 100 degrees F.
However, some say there should not be a problem here since it only gets that hot in mid-to-late summer, if at all.
“During the summer season, the insect can infest isolated fields, and there are many cases of a pest that has established itself in an area, because it has been able to acclimatize itself, so we need to be alert and cautious,” Reddy said.
Reddy said he contacted Dr. Sanford Eigenbrode, at the University of Idaho, who reported there is little likelihood of the Southern cowpea weevil overwintering in Montana or Idaho – as least as this time.
“Dr. Eigenbrode explained the low temperatures in Montana’s climate are not well tolerated by the cowpea weevils’ egg and larval stages,” he said. “An example of that is at 14 degrees F, the eggs can die off in less than three hours and at 41 degrees F, the eggs can die off in five days.”
The Southern cowpea weevil adult does not live long after emergence from the pupa (sleeping stage). It “crushes its way out of the seed, leaving a distinctive curved exit hole in the seed’s casing.”
The adult weevil is about 0.16 inches in length and is brownish in color (some look greenish brown) and all have wings. To defend itself, the adult weevils may “play dead’’ when disturbed and then resume their movement after 5–10 minutes.
This is also a common feature in many other beetles and weevils.
The adult weevils live for a short period of time (about two weeks) and are known as very fast fliers and fast runners.
The Southern cowpea weevil can be distinguished from the pea weevil by the presence of very long legs and antennae and also by “its vast host range.”
“The pea weevil is host specific to peas whereas the Southern cowpea weevil can infest several legumes,” Reddy said.
Because seeds are stored, the cowpea weevil larvae may be feeding inside the seed when planted in the fields and it is possible the pest could take a stronghold in Montana, if conditions are ripe.
If Reddy begins to discover the Southern cowpea weevil has established in Montana fields, there are biological controls for the pest.
“There are parasitoids that feed on the larvae. We have been successful in introducing parasitoids for other pests, such as the wheat midge, and the parasitoids do work well,” he said.
In addition, there are chemical, cultural and biological management strategies for control of the insect.
As chemical management, fumigation of infested stored seeds and spraying the seeds with certain chemicals will minimize the infestation.
Good hygiene habits while storing the seeds and the removal of infested crop residue from the field are also other recommended practices for its management.
Drying and heating are other management strategies for an infestation of seeds without affecting seed germination.
Once they are in stored seeds, heating to 135 degrees F for three to four hours can kill them.
One of the best ways to control the establishment of the Southern cowpea weevil is to check every shipment of seeds, and carefully examine seeds.
Seed companies are fastidious about examining seeds, but it is also a good idea to check seeds again before planting when it is still possible for the seeds to be replaced.
“Pulse production is affected by insect pests and disease infestations, which can cause major economic losses,” Reddy said. “In the early stages of infestation, the Southern cowpea weevil may go unnoticed, and only after the presence of exit holes, would someone realize the pest has affected the seed. Definitely, it takes vigilance for all of us to keep this insect under control in Montana.”
If somebody notices any damage to seeds and presence of exit holes on any legumes, please contact Reddy or the Entomology/Ecology team members at WTARC, phone 406-278-7707 or email, email@example.com.
Reddy said some acreages of lentils may be down this year in Montana due to lower prices, but there will still be a lot of pulses, including lentils, seeded across the state this spring.
“Along with cereal production, pulses are an integral part of Montana’s farming system, and we are a leading state in U.S. pulse production,” Reddy said.
Pulses are mainly harvested for dry seeds. Known as an excellent source for protein and other nutritional qualities, for producers, pulses improve soil health and create biodiversity across the farm.