Abstract
Tomato (Solanum esculentum) is one of the vegetable crops grown by both smallholder and commercial farmers in the Kingdom of Eswatini. Tomato leaf miner, Tuta absoluta M. is a major insect pest of tomatoes resulting in reduced tomato yields throughout the country. The study investigated the virulence of two sub-tropical EPN species on T. absoluta larvae. Steinernema yirgalemense and S. jeffreyense at different concentrations (0, 20, 40, 60 IJs/insect) were screened for efficacy (i.e. mortality rate) against larvae of T. absoluta in laboratory bioassays. Results obtained showed that S. yirgalemense and S. jeffreyense were able to kill T. absoluta larvae without significant differences between the two EPN species in 24-well bioassay trays. Significantly higher (p < 0.05) mortality was observed when 60 IJs/insect was used. The combination of S. yirgalemense at 60 IJs/insect (100%) and S. jeffreyense at 60 IJs/insect (98.3%) resulted in significantly higher (p < 0.05) mortality, compared with the other four combinations of EPN and concentration tested. In the leaf bioassays, S. yirgalemense (58.8%) resulted in significantly higher (p < 0.05) mean mortality compared to S. jeffreyense (46.4%). Steinernema yirgalemense at 60 IJs/insect resulted in significantly higher mean mortality compared to the other EPN and concentration combinations in the leaf bioassay. The results indicated that both EPNs tested were effective against T. absoluta larvae. Steinernema yirgalemense at 60 IJs/insect can effectively find T. absoluta larvae inside leaf mines, but large-scale field trials are recommended to demonstrate the potential use of the biocontrol agent within integrated pest management programs.
Highlights
Tomato plants are among the world’s most cultivated crops and they are cultivated by both smallholder and commercial farmers in the Kingdom of Eswatini (FAO, 2012)
All the four Entomopathogenic nematodes (EPNs) concentrations resulted in T. absoluta larval mortality that was significantly different (p < 0.05) from each other
Two EPN species, S. yirgalemense and S. jeffreyense isolated from sub-tropical environment, were used for the first time against T. absoluta larvae with successful control obtained for both species
Summary
Tomato plants are among the world’s most cultivated crops and they are cultivated by both smallholder and commercial farmers in the Kingdom of Eswatini (FAO, 2012). EPNs in the families Steinernematidae and Heterorhabditidae do not affect non-target species, do not leave residues (Georgis et al, 2006) and are essential biocontrol agents used for controlling insect pests (Grewal and Georgis, 1999). These EPNs are capable of penetrating and killing their hosts within 24–48 h of nematode invasion, which is caused by their mutualistic relationship with bacteria and of the genera Photorhabdus and Xenorhabdus that are carried in the intestine of Heterorhabditidae and Steinernematidae, respectively (Akhurst and Boemare, 1990; Husin, 2017). We tested the virulence of two sub-tropical EPN species on T. absoluta larvae
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