Lily leaf beetle

Appearance

Lily beetles, belong to the Order Coleoptera, Family Chrysomelidae. In general, adult lily beetles are around 6 to 9 mm in length. The adult's elytra 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 and a wide abdomen. Their antennae are made up of 11 segments. Furthermore, they have notched eyes and two apparent grooves on their thorax.

Naming

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 wing cases that are shinier with tiny dimples on them, they are more rounded in shape compared to the dull, narrow, flattened and elongated Cardinal beetle.. 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.

Distribution

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.

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 and Banchory in Aberdeenshire.

Behavior

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.

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. This process is known as stridulation and could even shock a bird or any other predator that may attack the lily leaf beetle.

Reproduction

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.

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 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.

Defense

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.

Often the first thing that observers notice is lumps of sticky brown frass, with the larvae inside, on lily leaves.