| Scarlet lily beetle | |
|---|---|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Coleoptera |
| Family: | Chrysomelidae |
| Subfamily: | Criocerinae |
| Genus: | Lilioceris |
| Species: | L. lilii |
| Binomial name | |
| Lilioceris lilii (Scopoli, 1763) |
|
The scarlet lily beetle (Lilioceris lilii), or red / leaf lily beetle, is a leaf beetle that eats the leaves, stem, buds and flower of lilies, fritillaries and other members of the family Liliaceae. They mainly lay their eggs on Lilium and Fritillaria species. Observed in absence of Lilium and Fritillaria species, the numbers of eggs laid were significantly less and the survival rate of eggs and larvae were lowered.[1] It is now a pest in most temperate climates where lilies are cultivated. Lily leaf beetles overwinter in the soil and come out early in spring whereas adults stay in moist environments.[2]
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Lily beetles (Lilioceris lilii), belong to the Order Coleoptera, Family Chrysomelidae. In general, adult lily beetles are around 6 to 9 mm (¼–⅜ in) in length. The adult's elytra (harder forewings) are shiny and bright scarlet in colour. The lily beetle's underside, legs, eyes, antennae and head are all pitch black, greatly contrasting the bright red colour of the wings. They have large eyes, a slim thorax (neck) and a wide abdomen.[3] Their antennae are made up of 11 segments. Furthermore, they have notched eyes and two apparent grooves on their thorax.[4]
Lily beetles are often confused with the Cardinal beetles as they also have a black underside and wings that are spotless and red in colour. However, the lily leaf beetles have wings that are shinier with tiny dimples on them, they are more rounded in shape compared to the dull, narrow, flattened and elongated Cardinal beetle.[5]. Another difference between the two is their food preference. Lily leaf beetles are herbivores and are usually found on lily plants eating their leaves whereas the cardinal beetles are usually found on tree bark and flowers and feed on flying insects.Lastly, the cardinal beetle has a comb-like antennae.[6]
Lily leaf beetles are fast fliers and hide very well. Additionally, when disturbed, they make a squeaky noise to deter predators. They could also be confused with unspotted ladybirds. Lily leaf beetles however are much slimmer than ladybirds.[3]
The lily leaf beetle is indigenous to parts of Europe and Asia. It is thought to have been introduced to North America through the import of plant bulbs around 1945. First spotted in Montreal, it has spread throughout Canada and the eastern United States within decades.[4] It has also become an invasive alien insect in the United Kingdom, where it has established itself after its introduction in 1943. It has since spread from Surrey to as far north as Glasgow.[7]
During the winter, adult lily leaf beetles rest in an undisturbed protective environment, normally shaded, cool and moist. Lily leaf beetles overwinter in soil or plant debris underneath the lily leaf plants they fed on during the previous summer and sometimes in gardens or woods quite a distance away from their host plants. In early spring, they emerge to feed on young lily leaves and mate.[3] Females can lay up to 450 eggs each season by laying about 12 eggs on the underside of an individual lily/fritillaria leaf in irregular lines along the midrib to conceal them. Hatching of the eggs occurs in about 6 days. The larvae begin to feed underneath the leaf and working up to the rest of the plant, feeding for up to 24 days. They then burrow themselves in the ground to pupate in a cocoon formed by saliva and small particles of soil. In about 20 days, they emerge as adults and continue to feed until winter. In some cases, they are able to go through this cycle more than once in a single year.[8]
Not only are the eggs laid underneath the leaf to stay hidden but they are also covered with a thick sticky brown substance for further protection. As larvae, they use their own frass (excrement) to make a protective shield, allowing protection from the sun and predators. However, the fecal shield is not an adequate protection against parasites - it actually acts as a chemical cue for the parasites to locate the larvae. [9] An adult that senses danger displays a defense mechanism, thanatosis, becoming motionless, folding up its appendages and falling with its black under surface facing up, thereby helping it camouflage with the ground to get away. If unable to escape, they are also able to ‘squeak’, by rubbing two parts of their body together, which may be used to startle the attacker.[10] This process is known as stridulation and could even shock a bird or any other predator that may attack the lily leaf beetle.[3]
Lily leaf beetles leave considerable damage on host plants. Managing ornamental lilies has become difficult in regions where lily leaf beetles have established. Damage to the leaves and flowers can also leave the plants weakened and susceptible to diseases such as Lily grey mold. [11]
The Canadian Maritime provinces, especially Fritillaria and Lilium gardens in Halifax, are largely affected by lily leaf beetles. A garden in Waverly, Nova Scotia has reported decline of lily species and cultivars from 50 in 1996 to only one species in 2006. [12] A newly discovered lily species in 2007, Lilium canadense, has raised the concern for protection of this Canadian native lily and control of the leaf lily beetle.
There are no registered chemicals for lily leaf beetle control, which limits options for the gardener. Although the most surefire strategy for preventing infestation by any pest is to avoid planting susceptible plants in the first place, with lily beetle this necessitates avoiding growing so many desirable cultivars of lilium, that other strategies may be preferred. Regular handpicking and crushing of eggs, larvae and adults is effective if somewhat laborious (adults can be drowned in soapy water if crushing is considered too violent). Domestic insecticides registered for general leaf beetle control containing carbaryl, methoxychlor, malathion and rotenone can prove useful in controlling populations.[4] However, malathion and carbaryl, effective on adults and larvae, are toxic to bees and other insects, respectively. [13] Products based on Neem extracts are useful in killing very young larvae and repelling adults without comparable harm to other insects, although this option is perhaps less effective than handpicking. Neem products should be applied every 5 to 7 days after egg hatch. Thiacloprid is also effective. [13] Floating row cover has been effective in preventing the adults from feeding and laying eggs in the spring. [14] [15]
There are no natural predators or parasites of lily leaf beetle in North America. In 1996, University of Rhode Island began testing the effectiveness of biological control of lily leaf beetle using six natural parasitoids in Europe. CAB International Bioscience Switzerland Center has also participated in this project from 1998 till 2001.[16]
Total parasitism rate in the last instar stage averages about 90% on wild lily Lilium martagon, 75% in gardens and 60% in cultivated lily fields in Europe. Most of lily leaf beetle parasitoids are wasps that lay eggs inside the host and effectively kill all infected individuals. Parasitoid wasp, Diaparsis jucunda Holmgren (Hymenoptera: Ichneumonidae), dominates over 90% of the parasitoid infections in lily leaf beetle. However, in gardens and commercial fields, Tetrastichus setifer (Hymenoptera: Eulophidae) and Lemophagus pulcher (Szepligeti) become the dominant parasitoids in the later season.[16]
University of Rhode Island experimented with release of European parasitoid wasp, Tetrastichus setifer, in Massachusetts from 1999 to 2001 to control for the lily leaf beetle population. The experiment had shown reduction of the beetle population. Population decline was also observed at another experiment site in Rhode Island. [17] In 2003, another parasitoid, Lemophagus errabundus, was also released in Massachusetts and is now established in the region. [12] Similar attempts of parasitoid release have been made in Boston with positive results.[18]
Lilioceris merdigera a similar species.