Introduction
⌅Tomato leaf miner (Tuta absoluta (Meyrick) (TLM)) is a devastating pest that can decrease fruit quality and cause up to 100% losses in Solanaceous crops in absence of control methods (11. Bueno VHP, van Lenteren JC, Calixto LAM Jr, Montes F, Silva D, Santiago LD, Pérez LM. New records of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) predation by Brazilian Hemipteran predatory bugs. J Appl Entomol. 2013; 137:29-34. https:// doi.org/10.1111/jen.12017 , 22. Biondi A, Guedes RNC, Wan FH, Desneux N. Ecology, worldwide spread, and management of the invasive South American tomato pinworm, Tuta absoluta: past, present, and future. Annual Review of Entomology. 2018; 63:239-258. ). The pest originated in South America and, after a rapid invasion, became a major threat to tomato production in Europe, Africa and Asia (33. Bawin T, Dujeu D, De Backer L, Francis F, Verheggen FJ. Ability of Tuta absoluta (Lepidoptera: Gelechiidae) to develop on alternative host plant species. The Canadian Entomologist. 2016; 148:434-442., 22. Biondi A, Guedes RNC, Wan FH, Desneux N. Ecology, worldwide spread, and management of the invasive South American tomato pinworm, Tuta absoluta: past, present, and future. Annual Review of Entomology. 2018; 63:239-258. ). Its presence was reported in Panama and Costa Rica (44. CABI Head Office, Wallingford, UK. 2016. Distribution Maps of Plant Pests, Tuta absoluta. [Distribution map]. Map 723 (1st revision). Consulted: 29/3/2018 available online: http://www.cabi.org/isc/datasheet/49260 ), and Caribbean countries such as Cuba and Dominican Republic are at high risk of being invaded, due to their proximity to infested areas, mainly after its first report in Haiti in 2019 (55. Verheggen F, Bertin R. First record of Tuta absoluta in Haiti. Entomologia Generalis. 2019; 38:349-353. https://doi.org/10.1127/entomologia/2019/0778 ).
In countries where the pest is present, the adopted integrated pest management (IPM) includes biological control augmentative or conservative, sex pheromone traps and use of selective insecticides (22. Biondi A, Guedes RNC, Wan FH, Desneux N. Ecology, worldwide spread, and management of the invasive South American tomato pinworm, Tuta absoluta: past, present, and future. Annual Review of Entomology. 2018; 63:239-258. , 66. Giorgini M, Guerrieri E, Cascone P, Gontijo L. Current Strategies and Future Outlook for Managing the Neotropical Tomato Pest Tuta absoluta (Meyrick) in the Mediterranean Basin. Neotrop Entomol. 2018. https://doi.org/10.1007/s13744-018-0636-1 ). However, the indiscriminate use of chemical pesticides may fail to successfully control the pest by inducing insect resistance (22. Biondi A, Guedes RNC, Wan FH, Desneux N. Ecology, worldwide spread, and management of the invasive South American tomato pinworm, Tuta absoluta: past, present, and future. Annual Review of Entomology. 2018; 63:239-258. ) and reducing the populations of natural enemies associated with the crops, and it also causes higher levels of residues on harvested tomato fruits (11. Bueno VHP, van Lenteren JC, Calixto LAM Jr, Montes F, Silva D, Santiago LD, Pérez LM. New records of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) predation by Brazilian Hemipteran predatory bugs. J Appl Entomol. 2013; 137:29-34. https:// doi.org/10.1111/jen.12017 ). Due to this problem, the development of tomato cultivars resistant to TLM was promoted in South America (77. Dias DM, Resende JT, Zeist AR, Gabriel A, Santos MH, Vilela NC. Resistance of processing tomato genotypes to leafminer (Tuta absoluta). Horticultura Brasileira 2019; 37(1): 40-46doi:10.1590/s0102-053620190106 ).
Solanum species such as S. peruvianum, S. hirsutum, S. galapagense, S. cheesmaniae and S. pimpinellifolium, among others, constitute a genetic background for breeding resistant tomato cultivars to TLM and other pests (88. Rakha M, Zekeya N, Sevgan S, Musembi M, Ramasamy S, Hanson P. Screening recently identified whitefly/spider mite-resistant wild tomato accessions for resistance to Tuta absoluta. Plant Breeding. 2017; 136(4):562-568doi:10.1111/pbr.12503 , 99. Maciel GM, Marquez GR, Silva EC, Andaló V, Belloti IF. Tomato genotypes with determinate growth and high acylsugar content presenting resistance to spider mite. Crop Breeding and Applied Biotechnology. 2018;18:1-8., 1010. Ghosh P, Jagadish KS, Purushothama MG, Hanson P, Rakha M, Sotelo-Cardona P, Vaddi S, Srinivasan R. Performance of Wild Tomato Accessions and Elucidation of Resistance against Invasive Pest Phthorimaea absoluta Damage under Tropical Conditions. Horticulturae. 2023; 9:143. https://doi.org/ 10.3390/horticulturae9020143 ). Currently, the most used Solanum species to develop resistant tomato cultivars are S. pennellii Correll and S. habrochaites Knapp & Spooner (1111. Resende NCV, Silva AA, Maluf WR, Resende JTV, Zeist AR, Gabriel A. Selection of tomato lines and populations for fruit shape and resistance to tomato leafminer. Horticultura Brasileira. 2020; 38:117-125. DOI - http://doi.org/10.1590/S0102-053620200202 ). Higher plants are capable to synthetize secondary metabolites to induce toxic metabolic effects, or of non-preference effects, to different harmful organisms (1212. Isah T. Stress and defense responses in plant secondary metabolites production. Biological Research. 2019; 52(39):1-25. doi:10.1186/s40659-019-0246-3 ). These compounds (toxic or repellent chemical substances) are synthetized on specialized plant structures (e.g., glandular trichomes in tomato) and help protect them against several arthropod pests (1313. Weinblum N, Cnaani A, Yaakov B, Sadeh A, Avraham L, Opatovsky I, Tzin V. Tomato Cultivars Resistant or Susceptible to Spider Mites Differ in Their Biosynthesis and Metabolic Profile of the Monoterpenoid Pathway. Front. Plant Sci. 2021; 12:630155. doi: 10.3389/fpls.2021.630155 ). The mechanisms of resistance detected in Solanum species are antixenosis (non-preference effects) and antibiosis (chemical compounds effects) associated with glandular or non-glandular trichomes (1414. Leite GLD. Resistencia de tomates a pragas. Unimontes Cientifica. Montes Claros. 2004; 2(6):130-140). These mechanisms reduce egg laying (i.e., female fertility) and larval feeding on TLM (22. Biondi A, Guedes RNC, Wan FH, Desneux N. Ecology, worldwide spread, and management of the invasive South American tomato pinworm, Tuta absoluta: past, present, and future. Annual Review of Entomology. 2018; 63:239-258. , 1515. Thomazini AP, Vendramim JD, Brunherotto R, Lopes MT. Efeito de Genótipos de Tomateiro sobre a Biologia e Oviposição de Tuta absoluta (Meyrick) (Lep.:Gelechiidae). Neotropical Entomology. 2001; 30(2):283-288. ) and increase adult longevity of the adults by the effect of methyl ketone 2-tridecanone present in the glandular trichomes (1515. Thomazini AP, Vendramim JD, Brunherotto R, Lopes MT. Efeito de Genótipos de Tomateiro sobre a Biologia e Oviposição de Tuta absoluta (Meyrick) (Lep.:Gelechiidae). Neotropical Entomology. 2001; 30(2):283-288. ).
The tomato cultivars may confer resistance against TLM by affecting its development time, survival and reproduction, among other biological parameters (1515. Thomazini AP, Vendramim JD, Brunherotto R, Lopes MT. Efeito de Genótipos de Tomateiro sobre a Biologia e Oviposição de Tuta absoluta (Meyrick) (Lep.:Gelechiidae). Neotropical Entomology. 2001; 30(2):283-288. ). For example, longer duration of larval and pupal stages, reduction of larval viability lower pupal weight and lower female fecundity of females in different lineages of cultivars belonging to Solanum lycopersicon L. have been found to indicate resistance to TLM under laboratory conditions (1616. Aslan B, Birgücü AK. Population parameters of the tomato leaf miner Tuta absoluta (Lepidoptera: Gelechiidae) on wild tomato species. Plant Protect. Sci. 2022; 58:315-325., 1717. Duarte L, Martínez MA, Bueno VHP. Biology and populational parameters of Tuta absoluta (Meyrick) under laboratory conditions. Rev. Protección Veg. 2015; 30(1):19-29. Cu-ID: https://cu-id.com/2247/ojs559.).
Moreover, the acyl sugar (AS) content present in tomato leaves is another factor related to resistance to arthropods. High AS contents confer resistance of cultivars to TLM and other pests. The use of hybrid lines obtained from at least one parent with high content of AS is enough to obtain hybrids resistant to a broad spectrum of crop pests (1111. Resende NCV, Silva AA, Maluf WR, Resende JTV, Zeist AR, Gabriel A. Selection of tomato lines and populations for fruit shape and resistance to tomato leafminer. Horticultura Brasileira. 2020; 38:117-125. DOI - http://doi.org/10.1590/S0102-053620200202 ). Another defense mechanism to TLM documented in tomato plants is the induced resistance generated by the larval feeding, which activates the metabolic pathway of jasmonic acid (JA) and, in turn, could make tomato less attractive to other pests associated with the crop and TLM more attractive to their natural enemies (22. Biondi A, Guedes RNC, Wan FH, Desneux N. Ecology, worldwide spread, and management of the invasive South American tomato pinworm, Tuta absoluta: past, present, and future. Annual Review of Entomology. 2018; 63:239-258. ).
In summary, knowledge about tomato genotypes and their resistance properties against TLM is a strength to be used in integrated pest management (IPM) programs (66. Giorgini M, Guerrieri E, Cascone P, Gontijo L. Current Strategies and Future Outlook for Managing the Neotropical Tomato Pest Tuta absoluta (Meyrick) in the Mediterranean Basin. Neotrop Entomol. 2018. https://doi.org/10.1007/s13744-018-0636-1 ). For areas at risk of being invaded by TLM, this advanced knowledge is a valuable element in an impact mitigation program. In the study, three tomato cultivars were included, two from Brazil (susceptible Solanum lycopersicum cv. Santa Clara) (1818. Oliveira CM, Júnior VCA, Maluf WR, Neiva IP, Maciel GM. Resistência de linhagens de tomateiro à traça Tuta absoluta, relacionada a aleloquímicos e à densidade de tricomas. Ciênc. agrotec. 2012; 36(1):45-52., 1717. Duarte L, Martínez MA, Bueno VHP. Biology and populational parameters of Tuta absoluta (Meyrick) under laboratory conditions. Rev. Protección Veg. 2015; 30(1):19-29. Cu-ID: https://cu-id.com/2247/ojs559.), TOM 687 (an improved line obtained from the original cross S. lycopersicum, with low AS content and S. pennellii LA-716, a feral accession with high AS content, and resistant to TLM) (1919. Maciel GM, Maluf WR, Silva VF, Gonçalves-Neto AC, Gomes LAA. Híbridos pré-comerciais resistentes a Tuta absoluta obtidos de linhagem de tomateiro rica em acilaçúcares. Horticultura Brasilera. 2011; 29:151-156. ) and the Cuban cultivar “Vyta” (obtained from the cross between S. lycopersicum and S. chilense) (2020. Alvares M, Moya C, Florido M, Plana D. Resultados de la mejora genética del tomate (Lycopersicon esculentum Mill.) y su incidencia en la producción hortícola de cuba. Cultivos Tropicales. 2003; 24(2):63-70. Cu-ID: https://cu-id.com/2050/ojs600.). In Cuba, Vyta is known for its resistance to TYLCV (Tomato yellow leaf curl virus) (2121. Dueñas F, Martínez Y, Álvarez M, Moya C, Peteira B, Arias Y, Diez MJ, Hanson O. Caracterizacion agromorfologica y evaluacion de la resistencia al TYLCV en nuevos genotipos de tomate (Solanum lycopersicum L.) como apoyo al programa de mejoramiento genêtico de la hortaliza para la enfermedad. Cultivos Tropicales. 2008 ; 29(1):53-60. Cu-ID: https://cu-id.com/2050/ojs264.). This genotype is used as a carrier of the Ty-1 gene to new commercial lines and is included within the official list of Cuban cultivars (2222. Gómez O, Piñón M, Martínez Y, Quiñónes M, Fonseca D, Laterrot H. Breeding for resistence to begomovirus in tropic-adapted tomato genotypes. Plant Breeding. 2004 ; 123(3):275-279., 2323. Dueñas-Hurtado F, Álvarez M, Moya C, Martínez-Zubiaur Y. Identificación del gen Ty.3, de resistencia a begomovirus, en accesiones de Solanum lycopersicum L. Cultivos Tropicales. 2011; 32(2):136-142. ). Also, biological parameters of TLM on Vyta, such as survival of larvae and adults, viability of pupae, total fecundity of females and sex ratio, were affected under laboratory conditions (1717. Duarte L, Martínez MA, Bueno VHP. Biology and populational parameters of Tuta absoluta (Meyrick) under laboratory conditions. Rev. Protección Veg. 2015; 30(1):19-29. Cu-ID: https://cu-id.com/2247/ojs559.). Taking into account these arguments, the aim of this study was to assess i) the non-preference effect measured by oviposition pattern of TLM females and ii) the antibiosis effect measured by larval survival on three tomato cultivars under semi-controlled conditions.
Materials and Methods
⌅The study was carried out at the Laboratory of Biological Control, Department of Entomology, and in a greenhouse, Department of Agriculture, Universidade Federal de Lavras (UFLA), Lavras, Minas Gerais, Brazil.
Plants obtaining
⌅Plants of three tomato cultivars (Vyta, Santa Clara and TOM 687) were used in TLM resistance trials. Seedlings and plants were obtained according to the methodology described by Duarte et al. (1717. Duarte L, Martínez MA, Bueno VHP. Biology and populational parameters of Tuta absoluta (Meyrick) under laboratory conditions. Rev. Protección Veg. 2015; 30(1):19-29. Cu-ID: https://cu-id.com/2247/ojs559.). The plants were subjected to 23±7,6oC of temperature, 64±15,4 % of RH and a natural photoperiod in a greenhouse with semi-controlled conditions. The temperature and RH values were recorded with a digital thermo-hygrograph Easylog USB®.
Insect rearing
⌅Tomato plants infested with eggs, larvae, and pupae of TLM were collected in areas of the campus of the Federal University of Lavras (Minas Gerais, Brazil), located at 21°14'S 45°00'W and 918 m a.s.l. Once in the laboratory, the emerged adults were released on tomato plants inside cages (90 cm x 70 cm x 70 cm) using the cultivar Santa Clara for rearing establishment of TLM at 25±2oC, 60±10 % RH., and a 12h photoperiod. New healthy tomato plants were regularly introduced into the cages to maintain a stock colony and feed the TLM larvae. For the experiments, individuals from the second generation reared on Vyta and TOM 687 cultivars were also used.
Experimental design
⌅Adult females (72h old) were transferred from the on-plant rearing to glass tubes (5ml) with the help of a compressor-vacuum machine (FANEM®), used for sucking small insects. The tubes were sealed with PVC® paper to avoid escape of insects. In parallel, 30-day-old tomato plants were placed in mesh cages with wooden frames (70 x 70 x 110 cm). TLM individuals were released inside the cages and, after 96h (i.e., four days), all adult females were removed with a manual vacuum cleaner. The number of eggs laid by females of TLM on leaves, stems, flowers and fruits was counted per plant. Similarly, after ten days, the number of living larvae on plants was assessed. Assessments were made separately on 10-15 cm of three plant strata, namely upper, middle and lower. The methodology described by Pratissoli et al. (2424. Pratissoli D, Parra JRP, Fernandes A, Oliveira RC, Zago HB, Pereira FF. Patrón de ovoposición de la polilla del tomate, Tuta absoluta, en tomates bajo diferentes densidades de poblaciones adultas en invernadero. Agro-Ciencia. 2003; 19(1):11-15.) was used as a reference. These authors assessed oviposition of different densities of TLM adults on S. lycopersicum var. Santa Cruz. However, we assessed oviposition and larval survival of a single adult density of TLM per treatment on different tomato cultivars.
The following experimental treatments were set up: (11. Bueno VHP, van Lenteren JC, Calixto LAM Jr, Montes F, Silva D, Santiago LD, Pérez LM. New records of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) predation by Brazilian Hemipteran predatory bugs. J Appl Entomol. 2013; 137:29-34. https:// doi.org/10.1111/jen.12017 ) two tomato plants (Santa Clara cultivar) + 40 female individuals TLM, (22. Biondi A, Guedes RNC, Wan FH, Desneux N. Ecology, worldwide spread, and management of the invasive South American tomato pinworm, Tuta absoluta: past, present, and future. Annual Review of Entomology. 2018; 63:239-258. ) two tomato plants (TOM 687 cultivar) + 40 female individuals TLM, (33. Bawin T, Dujeu D, De Backer L, Francis F, Verheggen FJ. Ability of Tuta absoluta (Lepidoptera: Gelechiidae) to develop on alternative host plant species. The Canadian Entomologist. 2016; 148:434-442.) two tomato plants (Vyta cultivar) + 40 female individuals TLM and (44. CABI Head Office, Wallingford, UK. 2016. Distribution Maps of Plant Pests, Tuta absoluta. [Distribution map]. Map 723 (1st revision). Consulted: 29/3/2018 available online: http://www.cabi.org/isc/datasheet/49260 ) three tomato plants (1 Santa Clara, 1 TOM 687 and 1 Vyta) + 60 individuals TLM. Fifteen replications per treatment were considered.
The Shapiro-Wilk test was used to explore the distribution data in all the experiments. Generalized Lineal Models (GLMs) with negative binomial distribution and log link function were used to analyse the effect of the fixed plant strata, tomato cultivar factors and their interactions with the number of eggs laid by TLM and number of active larvae for each experiment separately (i. e., with choice and without choice). To know the effect of tomato cultivars on the number of eggs and active larvae per plant strata, the variable ‘cultivar’ was stratified using GLMs with negative binomial distribution and log link function, followed by Tukey post-hoc tests adjusted for a family of 3 estimates. All statistical analyses were performed in R version 4.0.2 (2525. R Core Team R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing, Vienna, Austria. 2018. https://www.R-project.org/ ).
Results and Discussion
⌅For treatments without choice, the average number of eggs laid by TLM was significantly different among plant strata (X2=27,60, df=2, p<0,0001) and cultivars (X2=8,40, df=2, p=0,02). TLM female preferred to lay the higher quantity of eggs on the upper part of the plants, followed by the middle part and a lesser quantity of females on the lower part in Santa Clara cultivar (X2=32,47, df=2, p<0,0001). However, oviposition pattern of TLM did not show preference for plant strata in the other two cultivars (for TOM 687: X2=3,52, df=2, p<0,17; for Vyta: X2=3,90, df=2, p<0,14) (Fig. 1). The pattern of eggs in treatments with choice differed significantly only for plant strata (X2=20,25, df=2, p<0,0001). TLM females preferred the middle and upper strata of the plants to lay the higher number of eggs for all cultivars without significant differences (for Vyta: X2= 27,87, df=2, p=0,06; for TOM 687: X2= 20,15, df=2, p=0,11 and for Santa Clara: X2= 19,02, df=2, p=0,60). The quantity of TLM eggs in the lower plant strata was significantly less than the quantity laid in the middle and upper plants strata , respectively (for Vyta: X2= 27,87, df=2, p=0,0026, p<0,0001; for TOM 687: X2= 20,15, df=2, p=0,014, p<0,0001 and for Santa Clara: X2= 19,02, df=2, p=0,0004, p<0,0001) (Fig. 1).
The results of oviposition pattern of TLM females showed that the insect had a similar behaviour on Vyta and TOM 687 cultivars regarding the preference for the plant stratum to lay eggs. However, combining or not tomato cultivars influenced TLM preference. Females on non-combined cultivars (i. e., without choice) did not showed preference for any plant stratum, while on combined cultivars (i. e., with choice), they preferred the middle and upper part of the plants. However, the behaviour of TLM females on Santa Clara cultivar showed a different pattern and the cultivar combination also influenced the preference for oviposition. With non-combined cultivars (i. e., without choice), they showed clear preference for the upper plant stratum while with combined cultivars (i.e. with choice), no distinction was shown between the upper and middle strata.
Our findings agreed with Pratissoli et al. (2424. Pratissoli D, Parra JRP, Fernandes A, Oliveira RC, Zago HB, Pereira FF. Patrón de ovoposición de la polilla del tomate, Tuta absoluta, en tomates bajo diferentes densidades de poblaciones adultas en invernadero. Agro-Ciencia. 2003; 19(1):11-15.), who evaluated the oviposition preference for different densities of TLM on S. lycopersicum var. Santa Cruz and concluded that the pest prefered to lay the higher quantity of eggs in the upper plant stratum. However, this preference was evidenced only on Santa Clara cultivar offered individually. When the three cultivars were combined, the females preferred the upper plant stratum followed by the middle one .
TLM on Vyta and TOM 687 responded with less preference for oviposition when these cultivars were offered singly (Fig. 1 and Tab. 1). This suggests that antixenosis is the main mechanism of resistance involved. Such mechanism reduces the host properties of the plant and limits its use by insects for egg laying, feeding or shelter (2626. Mahmoud AMA, Ebadah IMA, Moawad SS, Mohmoud YA, EL-Hameid AR, Sadek HE. Tuta absoluta (Meyrick) resistance in tomato (Solanum lycopersicum L.) accessions and species. International Journal of Pest Management. 2022. https://doi.org/10.1080/09670874.2022.2055195 ). Thomazini et al. (1515. Thomazini AP, Vendramim JD, Brunherotto R, Lopes MT. Efeito de Genótipos de Tomateiro sobre a Biologia e Oviposição de Tuta absoluta (Meyrick) (Lep.:Gelechiidae). Neotropical Entomology. 2001; 30(2):283-288. ) also attributes these mechanisms as being responsible for the egg-laying rate of TLM being lower on the feral accessions S. peruvianum (PI 134417) and S. hirsutum f. glabratum (LA 444-1) than on the commercial tomato cultivars . Additionally, this low preference of the insect on Vyta was observed in laboratory conditions (1717. Duarte L, Martínez MA, Bueno VHP. Biology and populational parameters of Tuta absoluta (Meyrick) under laboratory conditions. Rev. Protección Veg. 2015; 30(1):19-29. Cu-ID: https://cu-id.com/2247/ojs559.), and it could be associated with the repellent activity of the highly toxic volatile compounds, which could have inhibited oviposition by TLM females (2727. Gonçalves-Neto AC, Silva VF, Maluf WR, Maciel GM, Nizio DAC, Gomes LAA, Azevedo SM. Resistência à traça-do-tomateiro em plantas com altos teores de acilaçúcares nas folhas. Horticultura Brasileira. 2010;28: 203-208., 22. Biondi A, Guedes RNC, Wan FH, Desneux N. Ecology, worldwide spread, and management of the invasive South American tomato pinworm, Tuta absoluta: past, present, and future. Annual Review of Entomology. 2018; 63:239-258. ). High concentrations of 2-tridecanona, zingiberene and amino-acids (allelochemicals) produced by glandular trichomes in tomato plants may play an important role in resistance to TLM (1818. Oliveira CM, Júnior VCA, Maluf WR, Neiva IP, Maciel GM. Resistência de linhagens de tomateiro à traça Tuta absoluta, relacionada a aleloquímicos e à densidade de tricomas. Ciênc. agrotec. 2012; 36(1):45-52., 2626. Mahmoud AMA, Ebadah IMA, Moawad SS, Mohmoud YA, EL-Hameid AR, Sadek HE. Tuta absoluta (Meyrick) resistance in tomato (Solanum lycopersicum L.) accessions and species. International Journal of Pest Management. 2022. https://doi.org/10.1080/09670874.2022.2055195 ).
Moreover, TLM oviposition on hybrids from the pre-commercial cultivar TOM 687 with higher AS contents was lower than on lines such as TOM-650, TOM-694, TOM-699 and TOM-700 and the commercial varieties (Bravo, Bônus y Santa Clara), with lower AS (1919. Maciel GM, Maluf WR, Silva VF, Gonçalves-Neto AC, Gomes LAA. Híbridos pré-comerciais resistentes a Tuta absoluta obtidos de linhagem de tomateiro rica em acilaçúcares. Horticultura Brasilera. 2011; 29:151-156. ), confirming resistance of TOM-687 and susceptibility of Santa Clara to TLM. However, both TOM-687 and Santa Clara were shown more preferred by TLM to lay eggs than Vyta, (except TOM-687 as a non-combined treatment) (Tab. 1).
| Cultivars | Eggs | Larvae | ||||||
|---|---|---|---|---|---|---|---|---|
| With choice | Without choice | With choice | Without choice | |||||
| Total | Sd | Total | Sd | Total | Sd | Total | Sd | |
| Vyta | 700 | 4,5 | 927 | 6,3 | 375 | 2,3 | 279 | 2,2 |
| TOM 687 | 1495 | 10,6 | 924 | 5,3 | 320 | 2,1 | 249 | 1,4 |
| Santa Clara | 1188 | 8,0 | 1140 | 9,4 | 160 | 1,2 | 403 | 4,9 |
The high number of TLM live larvae agreed with the oviposition pattern of the pest. For treatments without choice, the average number of active larvae was significantly different among plant strata (X2=57.29, df=2, p<0.0001), cultivar (X2=27.19, df=2, p<0.0001) and their interaction (X2=29.52, df=2, p<0.0001). For TOM 687 cultivar, significant differences were between plant strata (X2=95.53, df=2, p<0.0001). The highest quantity of live TLM larvae was found in the upper plant stratum (p=0.0001) followed by the middle one, (p<0.0001); the lowest amount of live larvae was in the lower plant stratum (p<0.0001). However, significant differences related to number of active larvae were not observed between plant strata in Vyta and Santa Clara cultivars after paired data analysis despite the slight or high statistical significance for them, in the global analysis (For Vyta: X2=5.86, df=2, p=0.05; for Santa Clara: X2=24.98, df=2. p<0.0001) (Fig. 2).
For treatment with choice, the average number of active larvae was significantly different among plant strata (X2=13.69, df=2, p=0.001). For Vyta and TOM 687 cultivars, the highest numbers of active larvae were found in the upper and middle plant strata, significantly diffrering from the number of larvae present in the lower plant stratum, respectively (For Vyta: X2=14.20, df=2, p=0.0004, p=0.0062; for TOM 687: X2=20.63, df=2, p<0.0001, p=0.0026). For Santa Clara cultivar, significant differences were only observed between the number of active larvae in the upper and lower strata of the plants (X2=10.15, df=2, p=0.0033) (Fig. 2).
Moreover, the similar response of TLM larvae survival in Vyta and in TOM 687 cultivar (Tab. 1) could be explained by the negative effect of AS compounds present on the leaves of the genotypes evaluated on increasing their resistance. Higher contents of AS act against T. absoluta through resistance mechanisms as antibiosis and antixenosis (1010. Ghosh P, Jagadish KS, Purushothama MG, Hanson P, Rakha M, Sotelo-Cardona P, Vaddi S, Srinivasan R. Performance of Wild Tomato Accessions and Elucidation of Resistance against Invasive Pest Phthorimaea absoluta Damage under Tropical Conditions. Horticulturae. 2023; 9:143. https://doi.org/ 10.3390/horticulturae9020143 ). However, despite the important determination of these mechanisms on the results, other elements could be involved. According to Vuceti et al. (2828. Vucetic A, Dahlin I, Petrovic-Obradovic O, Glinwood R, Webster B, Ninkovic V. Volatile interaction between undamaged plants affects tritrophic interactions through changed plant volatile emission. Plant Signaling & Behavior. 2014; 9:e29517; PMID: 24927115. http://dx.doi.org/10.416.) and Isah (1212. Isah T. Stress and defense responses in plant secondary metabolites production. Biological Research. 2019; 52(39):1-25. doi:10.1186/s40659-019-0246-3 ), induction of volatile compounds or the immune response of the plants may modify insect behaviour. These authors’ results confirmed that the chemical compounds released by healthy, damaged or insect-attacked plants can affect neighbouring plants and allow interactions that influence herbivores and natural enemies. The term "Allelobiosis" describes the links between allelopathy and insect behaviour (2929. Glinwood R, Ninkovic V, Jan P. Chemical interaction between undamaged plants: Effects on herbivores and natural enemies. Phytochemistry. 2011; 72(13):1683-1689. ).
Such arguments mentioned above may explain why Santa Clara in combination with other cultivars was less affected by TLM larvae and TOM 687 combined was more attractive for TLM females to lay eggs (Tab. 1). Also, Junior et al. (2012) found the influence of this factor in larval attraction when they assessed non-preference of TLM larvae for feeding on different substrates.
Different classes of volatile compounds suggest having a unique role in plant defence against herbivorous insects. However, each compound includes and establishes specific roles. Due to the low molecular weight, lipophilic nature and high vapour pressures at ordinary temperatures of monoterpenes and sesquiterpenes, they can transmit long-distance signals in the culture environment (3030. Midzi J, Jeffery DW, Baumann U, Rogiers S, Tyerman SD, Pagay V. Stress-Induced Volatile Emissions and Signalling in Inter-Plant Communication. Plants. 2022; 11:2566. https://doi.org/10.3390/ plants11192566 ). However, not only secondary metabolite accumulation plays a role in plant defence, but also phytohormone signalling as salicylic acid (SA), jasmonic acid (JA), abscisic acid (ABA), and ethylene (ET) strongly contribute to the attraction or repellence of pests or natural enemies (1313. Weinblum N, Cnaani A, Yaakov B, Sadeh A, Avraham L, Opatovsky I, Tzin V. Tomato Cultivars Resistant or Susceptible to Spider Mites Differ in Their Biosynthesis and Metabolic Profile of the Monoterpenoid Pathway. Front. Plant Sci. 2021; 12:630155. doi: 10.3389/fpls.2021.630155 ).
In our study, combination of tomato genotypes evokes contrary effects on TOM 687 and Santa Clara against TLM, because this combination modified their response, as it is observed in Tab. 1. However, these are the first results of a Cuban tomato cultivar against TLM and other studies are needed to characterize Vyta according to its AS contents or volatile compounds, which could explain the response of this cultivar against the pest. In this sense, practical implications should be evaluated since S. lycopersicum releases a diverse mixture of volatile compounds from its stem, leaves, flowers and fruits throughout its vegetative cycle (3131. D’Esposito D, Manzo D, Ricciardi A, Garonna AP, De Natale, A, Frusciante L, Pennacchio F, Ercolano MR. Tomato transcriptomic response to Tuta absoluta infestation. BMC Plant Biol. 2021; 21:358. https://doi.org/10.1186/s12870-021-03129-9 ). Other combinations of Cuban tomato varieties could be tested, including Vyta, to define the volatile profile of different parts of the plants in field conditions and that induced by the action of TLM since this mixture of volatiles could exert an impact on the insect (attraction or repellence), an effect that could be used as an alternative in this invasive pest management.
Based on our results, it can be concluded that the tomato leaf miner ‘TLM’ prefers to place the highest number of eggs on the upper and middle plant strata in the tomato cultivars assessed, mainly when they are combined. Also, the highest number of active larvae use these strata for feeding. This insect behaviour is an indicator to be considered in the sampling method for TLM. On the other hand, Vyta had a similar response to TOM 687 cultivar regarding the parameters evaluated. However, it was less preferred by TLM females for oviposition in combination with Santa Clara and TOM 687 cultivars. Combination of cultivars only influenced TOM 687 and Santa Clara, which suggests that Vyta has characteristics that confer it some level of resistance to this important pest. Our findings are very relevant for Cuban agriculture, as Vyta could be used as a first barrier to mitigate the impact of TLM damages, once the pest had invaded the country.