Entomologia Experimentalis et Applicata 96: 9–25, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands. 9 Searching and oviposition behavior of a mymarid egg parasitoid, Anagrus nigriventris, on five host plant species of its leafhopper host, Circulifer tenellus A.K. Al-Wahaibi & G.P. Walker Department of Entomology, University of California, Riverside, CA 92521, USA (Phone: 1 909 787 5808; Fax: 1 909 787 3086; E-mail: walker@citrus.ucr.edu) Accepted: February 10, 2000 Key words: Hymenoptera, Mymaridae, Homoptera, Cicadellidae, biological control, plant-insect interactions, tri- trophic interactions, behavioral ecology, beet leafhopper Abstract Searching and oviposition behavior and parasitization ability of Anagrus nigriventris Girault (Hymenoptera: Mymaridae), an egg parasitoid of beet leafhopper, Circulifer tenellus (Baker) (Homoptera: Cicadellidae), were examined on five host plant species of beet leafhopper: sugar beet (Beta vulgaris L.), red stem filaree (Erodium cicutarium [L.]), peppergrass (Lepidium nitidum Nuttall), desert plantain (Plantago ovata Forsskal), and London rocket (Sisymbrium irio L.). Beet leafhopper embeds its eggs in the tissues of these plant species. For each plant species, A. nigriventris behavior was examined on plants with and without beet leafhopper eggs. Experimental design was a 5 (plant species) by 2 (host eggs present/absent) factorial. Additionally within each treatment, par- asitoid behavior was observed over a 22-h period at five different observation periods: t = 0, 3, 6, 9, and 22 h where t = 0 h represents initial exposure of the insect with the plant. The behavioral events observed were: ‘fast walking’ (general searching), ‘slow walking’ (intensive searching), ovipositor probing, grooming, feeding, and resting. Significant differences (α = 0.05) among plant species in time spent on the plant, percentage of host eggs parasitized, and behavioral variables associated with intensive searching and oviposition all indicated that the plant species fell into two groups: ‘preferred’ plants (sugar beet, London rocket, and peppergrass), and ‘unpreferred’ plants (filaree and plantago). These variables also indicated that the parasitoids spent more time on, searched more, probed more, and oviposited more in plants with host eggs than plants without host eggs. Consistent effects of time (over the observation periods from t = 0 to t = 22 h) generally were detected only in the preferred plant species that had host eggs present. In these cases, intensive searching and probing decreased as time advanced, while variables related to general searching (‘fast walking’) and abandoning host egg patches (leaving the plant) tended to increase over time. Introduction Beet leafhopper, Circulifer tenellus (Baker) (Hemiptera: Cicadellidae), was introduced into North America from the Palearctic region approximately 100 years ago (Bennett, 1971). Beet leafhopper is the only known vector of curly top virus in North America (Bennett, 1971; Davis et al., 1998). Curly top virus seriously affects many vegetable crops in the western United States such as sugar beet, tomato, peppers, spinach, beans, and various cucurbits (Annand, 1931; Lawson et al., 1951). Beet leafhopper also is a vec- tor of stubborn disease (caused by Spiroplasma citri, a mycoplasma-like organism) which affects a number of citrus varieties grown in California. In California’s San Joaquin Valley, beet leafhopper is a migratory insect and is present on sugar beet and other vegeta- bles from late spring to late summer. In the fall, it migrates towards the foothills on the west side of the San Joaquin Valley where it overwinters in reproduc- tive diapause on perennial plants (frequently Atriplex