Genetic homogeneity in South American tomato pinworm, Tuta absoluta: a new invasive pest to oriental region

Investigating the effects of species niche shifts on the potential distribution of Tuta absoluta (Lepidoptera: Gelechiidae) by using global occurrence data

Invasive species may occupy quite different environments in their invaded areas to native ones, which may intensively interfere with predicting potential distribution through ecological niche modeling (ENM). Here, we take the tomato leafminer Tuta absoluta Meyrick (Lepidoptera: Gelechiidae), a tomato pest, as an example to investigate this topic. We analyzed niche expansion, stability, unfilling, and Schoener's D by principal component analysis (PCA) ordination method to examine its realized niche shifts and to explore how ENM approaches are affected by niche shifts. We used 5 datasets: Asian, African, European, South American, and global occurrence records in this study. Results showed that high niche unfilling for the species' invaded areas in Asia (20%), Africa (12%), and Europe (37%), possibly due to T. absoluta being in the early stages of invasion. High niche expansion was observed in Asia (38%) and Europe (19%), implying that some European and Asian populations had reached new climatic areas. African niche had the most niche stability (94%) and was equivalent to the native one in climate space (PCA ordination method), but the n-dimensional climate space framework showed that they were different. When projecting the native model to Asia and Europe, the native model performed poorly, implying that the niche shifts affected the transferability of the native model. ENM based on global data outperformed than other models, and our results suggested that T. absoluta has a large potential distribution in Asia, Mexico, South Europe, the United States, and Australia. Meanwhile, we recommend updating ENMs based on the species' invasion stage.

Migratory behaviour of Brown planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), in India as inferred from genetic diversity and reverse trajectory analysis

The brown planthopper, Nilaparvata lugens (Stål) is a major sucking insect pest of rice. This insect has long been considered as migratory; however, its route in India is still unknown. Hence, to find out its migration route genetic diversity, genetic structure and gene flow of 16 N. lugens populations from major rice growing regions of India was studied based on mitochondrial cytochrome oxidase I (COI). The results revealed a high genetic homogeneity among the populations on the basis of genetic diversity statistics and neutrality tests. There was a prevalence of a single major haplotype across the country. No spatial relevance was found with the genetic structure of the populations indicating presence of excessive gene flow among them. Extensive gene flow among populations was also confirmed with the presence of higher number of immigrants in North, Central, and East India. To further clarify the migration sources, 48 h air-mass reverse trajectory was performed for Varanasi just aftermath of cyclones Amphan and Yaas, which disclosed Eastern/Northeastern states along with Bangladesh and Myanmar as the possible source areas. Overall, the results revealed a single panmictic homogeneous population of N. lugens in India with extensive gene flow as a consequence of their migration. These findings will help in better forecasting enabling efficient regional management of this important rice pest.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03337-6.

Molecular diversity of Sesamia inferens (Walker, 1856) (Lepidoptera: Noctuidae) from India

Pink stem borer, Sesamia inferens (Walker, 1856) (Lepidoptera: Noctuidae) is reported to infest many graminaceous crops and cause significant losses. S. inferens cause damage by killing the central shoot and producing a characteristic symptom called "dead heart". Since graminaceous crops are an important source of food for humans and their livestock, impetus should be given on designing efficient management strategies against pink stem borer. The study of genetic variability of pest populations enables to interpret the ecological investigations correctly and also helps to comprehend the dissimilar response of pest to management tactics. The present study was undertaken to evaluate the diversity in S. inferens populations using mitochondrial cytochrome oxidase subunit I sequences from India, Pakistan, China and Indonesia. Analysis revealed a very low nucleotide diversity in Indian populations (π = 0.00981), as compared to a high nucleotide diversity in the sequences outside India (π = 0.4989). The phylogenetic analysis also did not show any clustering among populations within India and Pakistan. However, the nearest neighbour for the Indian and Pakistan population is a sequence from Indonesia followed by China indicating possible ancestral background. This is the maiden attempt to assess the molecular diversity of Indian populations in comparison to populations from other Asian countries.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02678-y.

Diversity analysis reveals genetic homogeneity among Indian populations of legume pod borer, Maruca vitrata (F.)

Legume pod borer, Maruca vitrata, has lately emerged as one of the major insect pests of pigeonpea causing considerable crop losses. Thus, efficient management of M. vitrata is an important component for sustained pigeonpea productivity for which information on insect diversity could be useful. Present study was undertaken to evaluate the diversity in M. vitrata populations collected from major pigeonpea growing areas of India using molecular markers, Cytochrome C Oxidase subunit 1 (cox1) and Translational Elongation Factor-1α (tef-1α). Genomic DNA from larvae of different populations was extracted; 709 bp and 550 bp fragments of cox1 and tef-1α were PCR-amplified, cloned and sequenced. Comparison of sequences of different populations using multiple sequence alignment did not show any differences in cox1 and tef-1α sequences within the Indian populations. However, further analysis based upon cox1 sequences has revealed moderate nucleotide diversity (π = 0.26174) among Indian and global M. vitrata populations, whereas nucleotide diversity within Indian populations is nonsignificant (π = 0.00226). Additionally, phylogenetic analysis of cox1 sequences grouped all the Indian populations into one cluster while that of global were completely separate indicating a different ancestral background. This is a maiden attempt for diversity assessment of Indian M. vitrata populations that established them to be genetic homologs with different ancestral background.

Current Strategies and Future Outlook for Managing the Neotropical Tomato Pest Tuta absoluta (Meyrick) in the Mediterranean Basin

The invasion of new regions by exotic pests has been more than ever a critical issue that warrants coordinated international actions to manage established populations and prevent further spreading. Invasive insects can undermine the ecological equilibrium of both natural and agricultural ecosystems. Moreover, increasing temperatures due to climatic change exacerbate this problem by allowing pests to further reach regions previously considered unsuitable. The tomato pinworm Tuta absoluta (Meyrick) (Lepidoptera) is an exotic pest native to Peru that has spread beyond Neotropical America. In Europe, its occurrence was reported in Spain in 2006, and thereafter, it has spread throughout the Mediterranean Basin and further into Africa and part of Asia. While T. absoluta can cause losses to tomato production all over the globe, the differences in each invaded region (e.g., climate, vegetation) may affect its population dynamics and, consequently, management protocols. Therefore, the main intent of this forum paper is to explore how European growers and researchers are dealing with T. absoluta in the Mediterranean area. As for many other invasive pests, the best approach has been the adoption of integrated pest management (IPM). Specifically, the integration of biological control agents (e.g., mirid predators and egg parasitoids), microbial insecticides (i.e., Bacillus thuringiensis), selective chemical insecticides, and sex pheromone-based control has proven adequate, especially in tomato greenhouses. Nonetheless, some of the challenges ahead include the development of resistant tomato cultivars, the management of wild vegetation and companion plants to optimize the conservation of natural enemies and their effectiveness at the crop level, the management of insecticide resistance, and the improvement of sex pheromone-based tactics.