Vigna unguiculata is a vital vegetable crop in Southeast Asia, and Megalurothrips usitatus can cause huge damage to this crop. Enhancing the resistance of V. unguiculata against M. usitatus is a promising way to protect this crop; however, there is limited information regarding the mechanism underlying the resistance of V. unguiculata against M. usitatus. Here, a behavior assay was performed to explore the resistance of V. unguiculata against M. usitatus after insect damage or treatment by jasmonic acid (JA). Furthermore, transcriptome and metabonomics analysis was used to detect the putative mechanism underlying the resistance of V. unguiculata against M. usitatus. The pre-treatment of Vigna unguiculata with JA or infestation with Megalurothrips usitatus alleviated the damage resulting from the pest insect. We further identified differentially expressed genes and different metabolites involved in flavonoid biosynthesis and alpha-linolenic acid metabolism. Genes of chalcone reductase and shikimate O-hydroxycinnamoyltransferase involved in flavonoid biosynthesis, as well as lipoxygenase and acyl-CoA oxidase involved in alpha-linolenic acid metabolism, were upregulated in plants after herbivory or JA supplementation. The upregulation of these genes contributed to the high accumulation of metabolites involved in flavonoid biosynthesis and the alpha-linolenic acid metabolism pathway. These transcriptional and metabolite changes are potentially responsible for plant defense and a putative regulatory model is thus proposed to illustrate the cowpea defense mechanism against insect attack. Our study provides candidate targets for the breeding of varieties with resistance to insect herbivory by molecular technology.

Megalurothrips usitatus (Bagnall) (Thysanoptera: Thripidae) is an important pest of cowpeas, Vigna unguiculata (L.) Walp., and can cause severe damage to the crop. Lasioseius lindquisti (Tseng) (Acari: Blattisociidae) and Lasioseius scapulatus (Kennett) (Acari: Blattisociidae) are 2 mites used against M. usitatus in Hainnan, China. The functional responses of these mites were examined in the laboratory. Lasioseius lindquisti showed a type III functional response, with a maximum prey consumption of 22.38 ± 0.63 per day. Its optimal search density for each unit in this experiment was 10.27 ± 0.50 per day. Lasioseius scapulatus showed a type II functional and an attack rate on 1st instars of M. usitatus of 0.83 ± 0.23. The handling time (h) of L. scapulatus was 0.074 ± 0.018 (means ± SE), while the maximum attack rate (T/Th) of adult females on 1st instar thrips was 13.51. Our results showed that both L. lindquisti and L. scapulatus are potentially useful predators of M. usitatus.

Megalurothrips usitatus (Bagnall) (Thysanoptera: Thripidae) is a serious insect pest, causing severe damage to crops in Southeast Asia and Hainan Province, China. The misuse of chemical pesticides has led to high resistance in pests to many pesticides. Physical control is an alternative method that is environmentally friendly. We investigated the effects of silver-gray plastic film on the behavior of M. usitatus on cowpea (Vigna ungiculata). The observations of behavior found that the silver-gray plastic film has different repellent effects on female and male thrips, with a repellency rate of over 90% for male thrips, while it repels female thrips at a rate of 85% in the laboratory. Field surveys have found that the number of M. usitatus arrived at the first peak at 7:00–9:00 a.m., and then gradually decreased, reaching its lowest point by noon, and then gradually increased to reach the second peak at 13:00–15:00 p.m. on a sunny day. In the climbing period of yardlong beans, before flowering, despite the increasing numbers of thrips, we found that the number of thrips in the silver-gray plastic film hanging area was significantly lower than that in the control area. During the early and late stages of flowering, the number of thrips in the silver-gray plastic film hanging area was significantly lower than that in the control area, but during the peak flowering period, there was no significant difference in thrips numbers between the areas with silver-gray plastic film and the control areas. These results indicate that the silver-gray plastic film is a potential method to decrease damage from M. usitatus, especially in the early stages of crop growth.