Fidelity of the Asian beetle Lilioceris egena (Weise) to air potato (Dioscorea bulbifera L.)

Authors: Dray, F Allen; ANYELINA, MANGRU - Florida International University; Goldstein, Scott

Submitted to: Meeting Abstract
Publication Type: Other
Publication Acceptance Date: 1/4/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: The invasive vine Dioscorea bulbifera (air potato) is a serious weed of natural areas in Florida trellising over trees and thereby suppressing native vegetation. The vine has spread into Georgia, and has the potential to spread to adjoining states as far north as Tennessee/southern Virginia. The beetle Lilioceris egena is being vetted for use as a possible biological control of this vine. The beetle preferentially attacks aerial storage organs (bulbils). This study assesses the beetles’ acceptance/rejection of plants with susceptible storage organs, comparing mortality, the volume of tissue consumed and numbers of eggs deposited on these potential host plant species.

Technical Abstract: TECHNICAL ABSTRACT The invasive Asian vine Dioscorea bulbifera (air potato) trellises up native trees in a variety of habitats in Florida and displaces native understory vegetation with its associated fauna, thereby altering community composition. A biological control program directed at this vine has already released one leaf beetle, Lilioceris cheni, that has rapidly spread throughout the state and is significantly stressing the target weed. Ongoing research suggests that the closely related L. egena, discovered in China, prefers aerial tubers (storage organs called bulbils) to foliage as a food resource and ovipositional substrate. However, susceptibility of storage organs from other plant species is not known. This study determined that the beetles’ fidelity to D. bulbifera as a food and ovipositional host, and therefore its suitability as a biological control agent. METHODS Lilioceris egena beetles collected in Yunnan Province, China, during May 2011 were used to establish two colonies of 200-250 adults each. Colonies consisted of D. bulbifera bulbils and substrate (soil or vermiculite) in plexiglass cages with a clear front and screened back. Bulbils and substrate were replaced weekly. Egg-infested bulbils were placed in emergence cages, where larvae eclosed and developed. After 10-14 days larvae began exiting bulbils to pupate in the substrate. Adults emerged 7-14 days later, and were removed to smaller cages containing a Gatorade/honey solution. These naïve adults were held for a 10 day pre-ovipositional period before being included in trials. Larvae for trials were obtained by isolating eggs from the colonies on moist filter paper where they were allowed to eclose. Some of the resulting neonates were placed directly onto test plant storage organs that had been sliced to remove a portion of the epidermis. Other neonates were first placed on D. bulbifera bulbil slices and allowed to develop for 4-5 days into 2nd/3rd instar larvae. They were then dissected out of the bulbil slices and transferred onto test plant storage organs. Trial units consisted of placing three (2', 1') adult beetles, three 2nd/3rd instar larvae, or five neonates in a container with a plant storage organ on filter paper (kept moist), and monitoring for mortality, feeding, and fecundity. Replicates consisted of 5 trial units from the test species plus at least one D. bulbifera bulbil. The amount of feeding was measured volumetrically. RESULTS Lilioceris egena adults and larvae failed to complete development on any plant storage organs other than D. bulbifera. Similarly, female beetles refused to oviposit on anything other than D. bulbifera bulbils and tubers. Feeding damage by adults, neonate larvae, and later instar larvae on plants other than D. bulbifera represented only test feeding, totaling less than 5% of the D. bulbifera tissue consumed. CONCLUSION The beetle Lilioceris egena is so closely adapted to the vine Dioscorea bulbifera that these insects will only feed, develop, and deposit eggs on the aerial tubers of that plant. It is therefore safe for release as a biological control agent. The one-two punch of L. cheni and L. egena should sufficiently stress individual D. bulbifera plants that multi-year recovery is disrupted and population declines become widespread.