Insecticide compatibility with the predatory ring-legged earwig Euborelia annulipes increases mortality of diamondback moth

Abstract

ABSTRACT Brassica growers rely on insecticides to control the diamondback moth (DBM) Plutella xylostella (L.), resulting in cases of insecticide resistance and control failure. The ring-legged earwig Euborellia annulipes (Lucas) is found in brassica fields and may prey upon DBM eggs, larvae, and pupae. Therefore, preservation of E. annulipes in brassica crops could enhance DBM control, and may help with DBM insecticide resistance management. The insecticides azadirachtin, chlorantraniliprole, cyantraniliprole, deltamethrin, indoxacarb, methomyl, spinosad, and teflubenzuron were evaluated to assess mortality of E. annulipes adults and DBM larvae when exposed to insecticide dry residues, and predation rate upon DBM larvae and pupae. Euborellia annulipes exhibited survival >98% to all tested insecticides when exposed to label rates used on brassica crops against DBM. The highest mortality of DBM larvae confined on insecticide dry residue was 61% after 24 h exposure. This mortality significantly increased up to 92% when E. annulipes was present in the same period. Female of E. annulipes showed a preference for DBM larvae over pupae irrespective of ratio availability and insecticide combinations. When only larvae or pupae were available, up to nine larvae or four DBM pupae were consumed within 24 h. At the label rate for spraying brassica crops, all tested insecticides were compatible with E. annulipes and the predator added significant mortality to DBM larvae in the presence of insecticide residue. The findings reveal opportunities for integrating E. annulipes as a biological control agent into management programmes for DBM that cannot effectively rely on insecticides alone.