# The Multivariate Regression Models Suggested as Standardising Tools for Categorising Solitarious and Gregarious Groups of the Main Pest Locust, Schistocerca gregaria, Produce Reproducible Results

## TL;DR

Researchers developed and validated two multivariate regression models to reliably classify desert locusts into solitarious or gregarious phases, which is important for studying locust outbreaks.

## Contribution

The study validates two reproducible models for standardizing the classification of solitarious and gregarious desert locusts.

## Key findings

- The models performed consistently on new locust samples, confirming their validity.
- Both models successfully categorized solitarious, intermediate, and gregarious locust samples.
- Recommendations were made to improve model precision in classifying nymph and adult locusts.

## Abstract

Locusts can be at a state called the solitarious phase, associated with harmless populations, or at the gregarious phase, associated with outbreaks. Given the importance of the phenomenon, researchers are trying to reveal its molecular basis and find ways to tackle it. For this, assessing the phase state and comparing locusts is essential, and researchers have thus far used different formulae. To address the problem presented by the lack of standardised tools for such an essential task, we previously suggested two models as tools for standardising the method for assessing the main pest locust, Schistocerca gregaria. However, a theoretical work later cast doubts on the validity of such models and predicted that they would not work as well on future samples as in their initial application. Here, we use additional, different S. gregaria samples to test and assess the performance of these models. The results reaffirm the validity of the results of our previous work, since the models performed just as well on the present samples as they did in the previous ones. The models are thus reinstated as potential tools for standardising the way solitarious and gregarious S. gregaria samples are assessed and compared.

Outbreaks of the desert locust Schistocerca gregaria affect some of the poorest parts of Africa, with devastating outcomes. The key to understanding and dealing with this problematic adaptation to environmental changes is comparing gregarious and solitarious locusts, either in nature or in laboratories. Categorising locusts and detecting changes in their phase status is key to such comparisons, which have been hitherto based on applying mathematical models that use behavioural parameters and that each laboratory has to build anew for each experiment. All the models used thus far are different from one another. This implies differences in the tools used for the different experiments and by the different laboratories and, thus, potential noise in the results and interpretations. Standardising the way locusts are categorised is necessary if we want to reduce noise and errors. It is crucial if we seek to make the results and interpretations transferable and comparable between experiments and laboratories for such an important research area. To tackle this problem, we suggested two models as possible standardising tools. However, the problem of a lack of standardised tools re-emerged due to the doubts cast on the validity of those models. Here, we use samples from independent S. gregaria populations in order to test and validate those models. We discuss how successful the two models were at categorising solitarious, intermediate (transient), and gregarious nymph and adult S. gregaria samples. We highlight shortcomings and make more specific recommendations on the use of those models based on the precision differences they show when categorising solitarious and gregarious S. gregaria nymph and adult samples. Overall, both models have proven to be valid since their results were largely replicated and seem reproducible.