A very particular predator. The case of the earwig D. lineare (Dermaptera) that reduces damages caused by the fall armyworm (Noctuidae) in Maize

Abstract

The fall armyworm (FAW), Spodoptera frugiperda, is an important pest of many crops, causing important yield losses in the Americas. FAW control relied mainly on the use of GMO maize and synthetic pesticides, and as a result, resistant populations to both control strategies are common. Dermaptera are omnivorous insects that may be considered either damaging or helpful organisms within agroecosystems. The beneficial actions of Dermaptera in many crops have been previously described. Doru lineare has been observed preying on FWA egg masses in corn crops, and functional response studies demonstrated its predation efficiency on small larvae. The aim of this contribution was to evaluate the levels of damage caused by FAW to maize plants in the absence or presence of D. lineare with different densities. Experiments were done in field boxes (60x60x50 cm) covered with nylon mesh cloth and containing 20 corn plants. Each plant, at 12 BBCH phenological scale, was infested with 2 neonate larvae. We had three treatments: control (infested plants by FWA larvae), low density (infested plants + 2 adult earwigs) and high density (infested plants + 4 adult earwigs) with 10, 20 and 20 replicated respectively. Starved earwigs were put into the boxes 24 h after the plant FWA infestation. 10 days after the earwigs’ release, the living insects were counted and larvae misured. The protective effect of the predator was measured through the level of damage caused to the plants (visual scale of damages for FAW, Fernandez & Expósito, 2000), and the loss of biomass (epigeal part of plant`s dry weight). In the control, 74.5% of the plants showed high intensities of damages (level 4 and 5), associated to high yield losses, while 32.5% and 23.2 % of high levels of damages were registered when plants were protected by 2 or 4 earwigs respectively. Protected plants with 4 earwigs/20 plants were 1.5 times as heavy as the non-protected control, and those with 2 earwigs/20 plants 1.35 times as heavy as the control. A direct association between the decrease in damages caused by FWA larvae and the presence ofdifferent densities of earwigs was found.