Notes on the Ecology and Host Specificity of Microlarinus lareynii and M. lypriformis (Coleoptera: Curculionidae) and the Biological Control of Puncture Vine, Tribulus terrestris
The difficulty of controlling Tribulus terrestris L., a weed pest in the Western United States, by cultural and chemical methods led to the subsequent ecological and host-specificity studies of two weevils, Microlarinus lareynii (Jacquelin duVal) and M. lypriformis (Wollaston), which were found attacking this plant in India, the Near East, and throughout the Mediterranean region. The adults feed on the stems and leaves of Tribulus; the larvae of M. lareynii develop in the seeds whereas those of M. lypriformis tunnel and develop in the stems. Feeding on Tribulus terrestris or closely related Zygophyllaceae was essential for development of eggs and oviposition, although in the absence of Tribulus both species accepted other plants on which they fed and survived for different lengths of time. The occurrence of ooeyte retrogression and cessation of egg laying in ovipositing females when removed from Tribulus to feed on nonrelated hosts, confirmed a critical weevil-Tribulus relationship. When feeding under forced conditions, the weevils were capable of causing damage to some plants but when offered these same plants on a take-it or leave-it basis, or in the presence of Tribulus, no damage resulted. In late August and September newly emerged adults enter diapause and do not lay eggs until the reappearance of Tribulus in the spring. Both weevils have been released and recovered in the Western United States.