Biology of Zagella delicata (Hymenoptera : Trichogrammatidae), an egg parasitoid of the sharpshooter Tapajosa rubromarginata (Hemiptera : Clypeorrhyncha : Clcadellidae) in Argentina
Research on biological control of glassy-winged sharpshooter (GWSS) Homalodisca coagulata (Say) started in the 1990s. This sharpshooter, vector of Pierce's disease bacteria Xylella fastidiosa Wells, expanded its geographical distribution and it has become a very serious pest problem in several crops, especially grapes, in southern California. In 2000, a survey of sharpshooter egg parasitoids was initiated in Argentina. Fourteen species of egg-parasitoids were collected. We report here on laboratory studies of adult longevity, oviposition preference, sex ratio, and development time of Zagella delicata De Santis. Field result of the incidence on its hosts and seasonal occurrence also are provided. Zagella delicata produced one adult per host egg. The overall results indicated that 72.5% of the sharpshooter eggs exposed to Z. delicata were parasitized. Wasps emergence was 43.8%. In host plant searching preference tests, Z. delicata females parasitized 66.7% of host eggs on sugar cane, 57.0% of eggs on corn and 4.5% on citrus leaves. The development time (from oviposition to adult emergence) averaged 23.5 +/- 1.2 days. The average adult longevity was 10.3 +/- 5.8 days. Females lived longer than males (females: 12.2 +/- 5.6 days, males: 6.2 +/- 3.7 days). The sex ratio in the laboratory was 1: 2.1 (males/females). In a hyperparasitism test, no adults of Z. delicata emerged from eggs previously exposed to Gonatocerus tuberculifemur. Seasonal sampling carried out in San Miguel de Tucuman showed that Z. delicata occurred from spring to fall, with maximum abundance at the beginning of the spring, where 57.2% out of the 1568 sampled eggs were parasitized. Field and laboratory data suggest that Z. delicata could be a prospective biological control agent against other, exotic, proconiine sharpshooters including H. coagulata. However, the efficiency of Z. delicata is restricted to habitats dominated by grasses.