Effects of Two Plant Extracts on Larval Leafminer Liriomyza trifolii (Diptera: Agromyzidae) in Tomatoes

Aqueous extracts from two plants, Urginea maritima L. (Liliaceae) and Euphorbia myrsinites L. (Euphorbiaceae), were tested for their insecticidal activity against the leafminer Liriomyza trifolii (Burgess) on infested tomato, Lycopersicon esculentum Mill., plants in the laboratory and field. Two grams of plant material was extracted with 100 ml of water and then diluted 1:100, 1:50, and 1:25 with distilled water. Diluted plant extract was either applied to the infested tomato leaves or by soil drench and was compared with foliar application of cyromazine. All dilutions of both plant extracts caused significant control of the leafminer larvae and maintained populations below those of the nontreated control plants in all trials. Only at the most concentrated dilutions (1:25) were the plant extracts statistically similar to the cyromazine treatment. Furthermore, greenhouse yields from all of the foliar treatments were statistically similar to the cyromazine treatment and significantly better than the nontreated control. Four species of leafminer parasitoids were found in the greenhouse; however, the percentage of parasitism was significantly less in all treated replicates than in the nontreated control replicates. Aqueous extracts from these two plant extracts exhibited both translaminar and systemic activity and are potential candidates as new organic insecticides.