Entomopathogenic nematodes for control of the cotton cutworm Spodoptera litura in marigolds

Abstract

Spodoptera litura Fabricius (Lepidoptera: Noctuidae) is a major pest of marigolds in Thailand. It causes severe damage to flower quantity and quality. The most common control method is synthetic insecticides, although this method struggles to control hidden larvae inside flowers or buds and underground pupae. Entomopathogenic nematodes (EPNs) are widely used as biocontrol agents against many foliage and cryptic insects. The virulence of two commercial EPNs strains, Steinernema siamkayai (Stock, Somsook and Reid) and S. carpocapsae (Weiser), isolated in Thailand, were assessed against different developmental stages of S. litura. The younger larvae of first and third instar were more susceptible to S. siamkayai with the LD50 of 15.84 and 40.34 dauer juveniles (DJs) per host, whereas S. carpocapsae caused higher mortality in older larvae. Against the fifth instar larvae and pupae, the LD50 ranged between 54.37 and 607.97 DJs/host. Field experiments compared the effect of EPNs with farmer's practice (insecticides). EPNs treatments with S. siamkayai and S. carpocapsae significantly reduced the percentage of damaged flowers to 2.53 ± 1.2% and 2.97 ± 1.5%, respectively, compared with insecticide treatment at 4.21 ± 2.1% in the first trial. In trial 2, the insecticide treatment had the highest percentage of damaged flowers of 5.02 ± 5.7%. The benefit–cost ratio (BCR) of EPNs treatments ranged from 2.42 to 2.53 in the first trial and 1.24–1.50 in the second trial and was superior to insecticide treatments with 2.21 and 1.16 in the two trials.

Occurrence of entomopathogenic nematodes, Oscheius myriophilus Poinar in Thailand: Preliminary characterization of novel isolates and biological control potential against insect pests

“…However, the instar larvae of S. litura and S. exigua generally remain on the underside surface of leaves (Hilliou et al, 2021) while EPNs were generally target to the underground pests and trunk borers (Hazir et al, 2001; Shapiro‐Ilan et al, 2006). Many studies showed that EPN successfully killed the two insects in both larval and pupa stages when the EPNs were applied on the right methods in the greenhouse and field conditions (Burana et al, 2022; Noosidum et al, 2016). For examples, fire retardant gel (Barricade®) can improve S. carpocapsae virulence when applied to control S. litura larvae on surfaces such as bark or leaves.…”

“…In marigold farms, the two insects also feed inside flowers or buds and underground pupae. The first and third instar larvae of S. litura were more susceptible to Steinernema siamkayai Stock, Somsook & Reid, whereas S. carpocapsae caused higher mortality in the fifth instar larvae and pupae (Burana et al, 2022). Moreover, S. exigua pupae showed high susceptibility to S. carpocapsae (Kaya & Hara, 1981), and to Steinernema riobrave Cabanillas, Poinar & Raulston (Henneberry et al, 1995).…”

“…The tobacco cutworm, Spodoptera litura F., and the beet armyworm, Spodoptera exigua Hübner (Lepidoptera: Noctuidae) are lepidopteran insects whose larval stages are economically important pests of various vegetable crops in the tropical and sub‐tropical regions (Ahmad & Mahmood, 2015; Li et al, 2015; Burana et al, 2022). The two polyphagous insect pests feed on over 100 host plants such as crucifers, onions, maize, rice, cotton, legumes, and vegetable crops (Hilliou et al, 2021).…”

“…Developing an environmentally friendly method to control insect pest populations, such as entomopathogenic nematodes, can help to reduce insecticides' harmful effects (Shapiro‐Ilan et al, 2002, 2006; Stock & Goodrich‐Blair, 2012). However, numerous reports indicate that the larval and pre‐pupa stages of the two insect pests are also vulnerable to many entomopathogenic nematodes (Burana et al, 2022; Garcia‐del‐Pino et al, 2018; Noosidum et al, 2016).…”

“…The tobacco cutworm, Spodoptera litura F., and the beet armyworm, Spodoptera exigua Hübner (Lepidoptera: Noctuidae) are lepidopteran insects whose larval stages are economically important pests of various vegetable crops in the tropical and sub-tropical regions (Ahmad & Mahmood, 2015;Li et al, 2015;Burana et al, 2022).…”