LILY LEAF BEETLE RESISTANCE AMONG LILY HYBRIDS

1. LILY LEAF BEETLE RESISTANCE AMONG LILY HYBRIDS Caitlyn MacGlaflin1, Lisa Tewksbury1, Dr. Richard Casagrande1. 1Department of Plant Sciences, University of Rhode Island, Kingston, RI 02881 INTRODUCTION The lily leaf beetle, Lilioceris lili, an invasive beetle native to Eurasia, was first discovered in Massachusetts in 1992 and is now distributed throughout New England. The adult (Fig. 1) and larva (Fig. 2) exclusively feed on lilies and are serious pests of both native and cultivated lilies. The adult beetle oviposits on the underside of lily leaves, where the eggs (Fig. 3) hatch and larvae cause considerable damage to the plant by feeding on the leaves (Fig. 4). Lilies serve as important perennial plants and rank third among Dutch bulbs imported into the U.S. University of Rhode Island researchers have been investigating biological control techniques in order to control the beetles without the use of insecticides. Three host-specific parasitic wasps that regulate the beetle population in Europe have been introduced, and are currently being monitored to determine their impact on beetle populations. Another potential strategy to control the beetle is through the use of resistant lily hybrids. Livingston et al. (1996) found that Lilium henryi and Lilium speciosum, ‘uchida’, were not suitable hosts for lily leaf beetle larval development. Another lily hybrid that has been noted by growers to have some resistance to the lily leaf beetle is ‘Black Beauty’; this study was designed to test the resistance of the ‘Black Beauty’ hybrid. RESULTS The results indicate that the number of eggs laid, the number of first instar larvae, and the number of emerging adults were not significantly different between hybrids (P= 0.979, P= 0.294, and P=0.182, respectively). There was a significant difference in the number of fourth instar larvae surviving between hybrids (P= 0.000028) (Fig. 9). A significantly lower number of fourth instars survived on ‘Black Beauty’ than on Oriental Pink with means of 0.91 and 7.33, respectively. Fig. 5. ‘Black Beauty’ Hybrid Fig. 6. Oriental Pink Hybrid METHODS Lily hybrid resistance was measured by performing a no-choice experiment to evaluate oviposition (number of eggs laid), egg hatch, larval development, and pupation of the lily leaf beetle on two hybrids, ‘Black Beauty’ (Fig. 5) and the control hybrid, Oriental Pink (Fig. 6). One replicate consisted of one cage containing two lily plants of the same hybrid (Fig. 7). There were eleven ‘Black Beauty’ replicates and nine Oriental Pink replicates. Three mated pairs of lily leaf beetle adults were placed in each cage (Fig. 8) for oviposition. Temperature and humidity were maintained at 25º C and 40%, respectively. After four days the adults were removed, and the eggs were counted in each cage. Eggs were allowed to hatch on the plants and the larvae were counted every four days until all larvae had dropped off the plant and gone into the soil to pupate. The plants were removed from the cages, put into net sleeves, and watered and checked for adult emergence twice a week. Resistance of each hybrid to lily leaf beetle damage was determined by evaluating oviposition, first instar larvae, fourth instar larvae, and adults. These data were analyzed using a 2-sample t-test assuming equal variances. Fig. 2. Lily leaf beetle larvae. Fig. 1. Lily leaf beetle. Fig. 9. Mean number of lily leaf beetle by growth stage. Error bars are ± SE. DISCUSSION The results of this study suggest that lily leaf beetles will oviposit equally on both hybrids, that eggs were less likely to develop into fourth instars on the ‘Black Beauty,’ and that some of the larvae survived to adulthood on ‘Black Beauty’. We think that if the lily leaf beetle pupae had a higher survival rate that we would have observed a significant difference in the total number of adult emergence between the two hybrids. Black Beauty’s resistance may contribute to biological control of the lily leaf beetle. Further research should include an extension of the previous experiments on ‘Black Beauty’ hybrid and possibly isolate any compounds the ‘Black Beauty’ hybrid is producing that may contribute to the inhibition of larval development. Fig. 3. Lily leaf beetle eggs. Fig. 4. Damage by larvae. Fig. 8. Mating adults. Fig. 7. Cage with lilies. • LITERATURE CITED • Livingston, S.B.1996. Biology, control, and host range of Lilioceris lilii: a new ornamental pest in the USA. MS thesis, Univ. Of Rhode Island, Kingston. 78pp. • 2. Macrae, Edward A. Lilies. Portland: Timber Press, Inc.,1998. ACKNOWLDEGEMENTS Thanks to The New England Greenhouse Conference for project funding and also to Heather Faubert, Jason Winiarski, Nikki Nadeau, Aaron Weed, and David Viola for their invaluable assistance.