New predator insects may help fight major maize pests

Two newly identified parasitoids promise major benefits as biological control solutions for maize pests in Africa and Europe. Researchers Paul-André Calatayud, senior research scientist at the French Research Institute for Development, and Sevgan Subraman

Insect pests, such as maize stem borers and fall armyworm, increasingly challenge food production around the world.

Huge demands for crops have meant agricultural systems have simplified and frequently focused on single crops. In monocropping systems, when fields are full of a single crop, they can easily be found by their insect pests, as opposed to when mixed cropping is practised. Because of this, higher yield losses have more chance to occur in monocropping systems.

Climate change, which is mostly associated with increased temperatures and changes in rainfall patterns, as well as wild habitat reduction by farmers, have added to this by increasing pest pressure and resurgence.

The rapid evolution of pest resistance to chemicals, an increasing organic food market, and the negative effects of chemicals on the health of people and the environment, have increased the need to control insect pests biologically.

Insect predators

Biological control uses live organisms, such as insect predators, to kill or eat insect pests. Insect parasitoids are one form of biological control. These are insects that develop as parasites on other arthropods, mostly insects, causing their death or sterility.

They can target each developmental stage of the insect (eggs, larvae or pupae). These parasitoids have received increased attention because they are efficient, cheaper and offer a management strategy that safeguards human health and the environment.

Two species of these parasitoids have been discovered by us and our colleagues in Kenya. They have been found to be efficient biological control agents, including Cotesia typhae to control the maize stem borer Sesamia nonagrioides, and Cotesia icipe to control the fall armyworm, Spodoptera frugiperda.

S. nonagrioides is an African cereal stem borer that invaded Europe and the near and Middle East about 100 000 years ago. It has become a major pest for maize and, due to global warming, the pest has been spreading.

Fall armyworm is an invasive species, originally from tropical areas in the Americas, and invaded subSaharan Africa in 2016. It has now spread to Asia and Australia and has the potential to soon spread in Europe.

African countries have faced major maize shortages and billions of dollars’ worth of damage due to the devastation caused by the fall armyworm and the increased cost of pesticide applied.

There are other parasitoids that can kill these pests, but they are not always present in nature. Understanding the prevalence and effectiveness of these other parasitoids is important. We must ensure that the parasitoids that we introduce don’t interfere with

It was found to be an effective natural enemy of the fall armyworm in Africa.

Spodoptera frugiperda seriously limits maize yields by infesting the crop throughout its growth stages from seedling to maturity. The use of chemical pesticides seems to be the most common practice used to control the pest, but these can be harmful, particularly to the environment as they can affect non-targeted organisms, such as bees.

Through extensive field surveys in East Africa, several indigenous parasitoids, which attack the fall armyworm at its larval stage, were found.

This included a new species of parasitoid named C. icipe.

It successfully parasitised 45% of fall armyworm.

The next phase will focus on developing biological control of the fall armyworm in East Africa using C. icipe and other parasitoids.

These studies aim to propose a solution to the lack of full control methods against two major maize pests. It provides good biological control solutions that should fulfil environmental safety regulations while being efficient and economically sound.

We are now putting together feasibility studies for governments on introducing these parasitoids into their new environments.

• This article was first published by theconversation.com.