Lily Beetle Spotting & Prevention

What has got 6 legs, a head, 2 eyes and red wings and  is not a dice game of Beetle. It is the red lily beetle Lilioceris lilii that consumes large quantities of one of our favorite plants.

How to Spot Lily Beetle

  • Adults are 8mm long, bright red with a black head and legs.
  • Eggs are 1mm long and orange-red, found in groups on the underside of lily leaves and they hatch in around a week.
  • Larvae have orange bodies with black heads but are normally covered with their own slimy black excrement.
  • The fully grown larvae are 8-10mm long.
  • At the pupal stage they lie in the soil.
  • Both the adults and larvae can defoliate lilies and fritillaries in short order.
  • Leaves get ragged and black gungy deposits can be seen on infected plants.
  • The red beetles easily fall off leaves and hide in the soil when gardeners try to remove them by hand.
  • The beetle was initially confined to south east England but has spread north.

The Lily Beetle Cycle

  • Adult lily beetles emerge from the soil from late March to May and feed on  foliage between May and  September.
  • Adults feed and lay eggs on the underside of leaves of host plants from late April until early September.
  • After about two weeks, when the larvae are fully grown, they pupate in the soil. Two to three weeks later new adults emerge.
  • The beetles overwinter as adults in sheltered places, often in the soil but not necessarily near lilies.
  • This non-native pest became established just before the second world war.

Prevention, Predators and Parasites

  • Red lily beetle overwinters in soil, leaf litter and other sheltered places so good husbandry can help.
  • Small infestations can be picked off by hand. There is some pleasure in squashing a red beetle that has caused your plant so much damage.
  • There are some parasitic wasps but probably not enough to help your lilies survive.
  • The RHS to which I am indebted for this advice say ‘ Pesticides are likely to be more effective on larvae than adults
  • Heavy infestations which are impractical to remove by hand can be treated with pesticides
  • Organic insecticides containing natural pyrethrins  Several application of these short persistence products may be necessary to give good control
  • Synthetic pyrethroid pesticides such as lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), or deltamethrin (e.g. Sprayday Greenfly Killer) can be used
  • The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) can also be used’
  • In my experience it is wise not to expect miracles with chemical treatments and beware they can kill pollinating insects.

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