Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2004
Publication Date: 12/1/2004
Citation: Logarzo, G.A., Virla, E.G., Triapitsyn, S.V., Jones, W.A. 2004. Biology of zagella delicata de santis (hymenoptera:trichogrammatidae) egg parasitoid of tapajosa rubromarginata (signoret) (hemiptera:clypeorrhyncha:cicadellidae) in argentina. Florida Entomologist. 87(4):511-516 Interpretive Summary: The glassy-winged sharpshooter, Homalodisca coagulata Say (Homoptera: Cicadellidae), is native to the southeastern United States. Since the early 1990's, this insect has expanded its numbers and its range resulting in a very serious pest problem in crops (especially grapes in southern California. As xylem feeders, GWSS is an effective vector of the bacterial plant pathogen, Xylella fastidiosa. This bacterium is the causal organism for Pierce's Disease (PD) of grapes, phoney peach disease in the southern U.S., variegated chlorosis of citrus in Brazil and, most recently, oleander leaf scorch in southern California. GWSS could be a disaster in the grape industry. Only one biological control agent of any significance has been noted so far, the small egg parasite, Gonatocerus ashmeadi Girault (Hymenoptera: Mymaridae). Although parasitism rates have been high, 80-100%, there have been ample numbers of overwintering adult sharpshooters to produce problematic populations the following season. Natural control was not enough to control the pest. GWSS needs more work on management and biological control, including foreign exploration for BC agents for California. Reported herein are the results of laboratory and field studies of Zagella delicata De Santis, an Argentine egg parasitoid of a sharpshooter related to GWSS. Information is provided on its bionomic (adult longevity, oviposition preference, sex ratio, duration of development), the incidence on its host in the field, and seasonal occurrence. Comments are included regarding the potential of this egg parasitoid as a biological control agent of GWSS.
Technical Abstract: Research on biological control of glassy winged sharpshooter (GWSS), Homalodisca coagulata (Say) was started in the 1990s. This sharpshooter, vector of the bacteria Xylella fastidiosa, expanded its range and its numbers resulting in a very serious pest problem in several crops, especially grapes in southern California. In 2000, an exploration of sharpshooter egg parasitoids was initiated in Argentina. Fourteen egg-parasitoid species were collected. We report here the results of laboratory and field studies of one of them, Zagella delicata De Santis, providing information on their bionomics (adult longevity, oviposition preference, sex ratio, duration of development), the incidence on their hosts in the field, and seasonal occurrence. Zagella delicata produced only one adult per host egg. The overall results showed that 72.5% of the eggs exposed were parasitized, and that wasps emerged from 43.8% of these. In host plant searching preference tests, Z. delicata females parasitized 66.7% host eggs on sugar cane, 57.0% eggs on corn and no host eggs were attacked on citrus leaves. The duration of development (from oviposition to adult emergence) averaged 23.5 + or - 1.18 days. The average adult longevity was 10.30 + or - 5.77 days. Females lived longer than males (females: 12.2 + or - 5.6 days, males 6.2 + or - 3.7 days). The sex ratio in the laboratory was 1: 2.11 (males/females). In the hyperparasitism test, no adults of Z. delicata emerged from eggs previously exposed to Gonatocerus tuberculifemur. The 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 potential biological control agent aganist other, exotic, proconiine sharpshooters including H. coagulata. However, the efficency of Z. delicata is restricted to habitats dominated by grasses.