Beans production threatened by pest


The natural propagation of the Asian bean Thrips is causing concern for agriculture authorities as it is affecting a cash-producing crop, which is also the main ingredient to our typical Belizean meal. During a zoom meeting with the media on Thursday, experts from the Belize Agricultural Health Authority BAHA hypothesized that the pest has been in Belize for perhaps no more than six months given the nature of the epidemic. The Asian Thrips began with a very small population and it has increased exponentially, to now threaten our food security.
Megalurothrips usitatus, previously known as Taeniothrips nigricornis pest is a very tiny elongated yellow and dark insect measuring about two millimeters, found mainly affecting flowers, tender buds, and young leaves in the bean family (Fabaceae) and other target crops. It causes stunted growth and by affecting the flowers it reduces production by up to 100%.
Thrips damage the pods of beans. Infestations begin in the flowers (See Photo), and pods become twisted, deformed with reddish-brown russet marks developing as the thrips feed. Large infestations cause poor pod sets, stunted plants, and leaves and cause flowers to wilt. This species of thrips is not known to spread viruses.
Eggs are laid by the thrips in slots flowers and leaves cut by its ovipositor. The nymphs are yellow at first, but later deep yellow or orange-red. Pupae are formed in the soil. Adults and nymphs are readily seen when opening the flowers. The adults are greyish-brown, with the deepest colors on the head and striped abdominal segments.
Thrips are spread by active flight, but also winged adults and nymphs can be picked up by winds and carried long distances.
Farmers can look for the wilting of flowers and leaves, and adult thrips, and nymphs, in the flowers. Because of Megalurothrips usitatus similarity with other species, specimens should be sent for expert identification. Sticky traps are used to monitor and control some species of thrips, and could be tried for this species.
The results of delimiting surveys conducted by the Ministry of Agriculture, BAHA, and the Caribbean Agricultural Research and Development Institute CARDI have found that this pest is now distributed throughout the Country.
Thrips are known to affect other leguminous crops such as soybean, pigeon pea, lima bean, and even peanuts. BAHA has found the insects in soybean and peanuts in Belize as well as in other wild leguminous species. It is even known to affect potatoes, but the experts never found it affecting that commodity because of the early harvest.
In the case of Belize, the main bean crop for this year seems to have escaped the brunt of the infection because by the time the pest exploded perhaps 90% of the bean or more had already flowered and set pods. Any late planting of the commodities resulted in severe damages and is indicative of the very destructive nature of this pest for future plantings.
Jose Novelo, Director of the Grain Program at the Ministry of Agriculture also briefed the media on the pest on Thursday. According to Novelo, having run into problems with the availability of RK beans towards the end of 2020, the Ministry of Agriculture considered that it needed to get more information on what was being produced and the crops that were affected. What the Ministry of Agriculture discovered is that the damage was primarily in black eye peas.
Black-eyed peas are normally exported to CARICOM and other countries. Belize does not utilize many black-eyed peas, so that was a relief to the Ministry of Agriculture. However, beans are important for Belize. About six thousand acres were recently in production and the damage was between forty-five to fifty percent, and there have been heavy losses that were incurred in the black-eyed peas primarily in Corozal, Orange Walk, and the Cayo District. The estimated loss value of that six-thousand-acre crop was about 8.4 million dollars.
BAHA is concerned and all strategies have to be developed. The upcoming major bean crop is at the end of 2021 and the beginning of 2022, so it is very likely going to be affected. Experts within BAHA say that Belize has to have sound strategies by then to be able to fight this pest. This will entail a very strict monitoring program so that as soon as it is detected actions can be taken that it does not develop into massive populations. BAHA believes that even by then, natural controls in the environment are going to become activated and also help in suppressing the very high populations of this pest.
Several natural enemies feed on thrips. There are predatory thrips, minute pirate bugs, predatory mites, lacewing larvae, and ladybird beetles (adults and larvae). Parasitoids have been reported to affect thrips (eulophids), but their impact is not well known.
It is best to avoid pesticides to manage thrips, especially those pesticides that are long-lasting, as they will destroy populations of beneficial insects. Also, thrips develop resistance to pesticides easily.
Before planting avoid planting next to infested crops. Rotate crops with non-host plants to break the lifecycle. Avoid planting another food legume crop after beans.
During growth, intercrop with a non-host plant to slow the movement of thrips through the crop. For example, grow capsicum between yard-long beans. Destroy weeds within and around crops to prevent the build-up of thrips populations. Use a hose with a strong jet of water to remove thrips from the plants. Do away with crop remains after harvest to prevent thrips from spreading from old to young crops.
It is unlikely that thrips populations will be high enough to justify the use of pesticides. In any case, the use of pesticides is likely to do more harm than good, as they will kill natural enemies. Also, thrips tend to hide in sheltered places on plants, and within flower buds, thus they are difficult to reach with pesticides. If pesticides are applied, try plant-derived products (botanical sprays) first, and always try to treat the undersides of the leaves.
Do not use broad-spectrum insecticides such as dimethoate, malathion, and permethrin. They have a greater effect on the natural enemies of thrips than on the thrips.
“We are going to have to depend on a series of activities or a combination of integrity pest management activities using biocontrol agents such as predators. We are going to have to establish threshold levels which means determining what pest population you can come in with a measure of while the use of heavy pesticides is not recommended because it just turns into a vicious cycle of ever-increasing resistant pests,” affirms Francisco Gutierrez, Acting Managing Director, of BAHA.

Francisco Gutierrez

He continued, “At the very least we’ll probably be advising on the use of pesticides that are softer, that have a lot less impact on the environment such as plant-based extracts. All of these strategies are going to be pursued, but overall, what is going to be very critical is an educational and training campaign, so that we can get our farmers involved in this process.”
As a result of those heavy losses in this critically important crops, a task force has been formed to come up with solutions to the Asian bean thrip infestations. The task force includes representatives from the Ministry of Agriculture, BAHA, CARDI, the Regional Organization for Agricultural Health for Central America (OIRSA), the Pest Control Board, and grain producers.