Blue willow beetle

The blue willow beetle (Phratora vulgatissima), formerly Phyllodecta vulgatissima, is a herbivourous beetle of the family Chrysomelidae. It is dark with a metallic sheen that ranges from a blue color to bronze. It is distinguished from P. vitellinae by the latter more commonly displaying bronze coloration. European Phratora species can be distinguished based on morphology of female genitalia.^[1] The larvae undergo three instar stages from hatching to pupation.^[2] This beetle is found throughout Europe and Scandinavia,^[3] and occurs in China.^[4]

Blue willow beetle
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Coleoptera
Suborder:	Polyphaga
Infraorder:	Cucujiformia
Family:	Chrysomelidae
Genus:	Phratora
Species:	P. vulgatissima
Binomial name
Phratora vulgatissima (Linnaeus, 1758)

Ecology

The blue willow beetle is found on willow (Salix) species, whose leaves contain low levels of salicylates^[5][6] in fens, carrs and on river banks, but also often in willow short rotation coppice and other agricultural landscapes.^[7] It often aggregates on host plants.^[8] On Salix cinerea, it prefers and is more common on female than male trees despite higher egg predation exerted by the common flowerbug Anthocoris nemorum on female trees.^[9] It is univoltine in Sweden^[2] but can produce multiple generations per year in other parts of its distribution range.^[10] Proliferation of larvae and egg production varies with vegetation.^[11] It overwinters under lichens on trees and under tree bark.^[12] Predators of blue willow beetle eggs include A. nemorum and Orthotylus marginalis. Larval predators include A. nemorum, the bug Rhacognathus punctatus,^[10] a syrphid fly (possibly Parasyrphus nigritarsis)^[13] and the wasp Symmorphus bifasciatus.^[14] Adult beetles are parasitized by the wasp Perilitus brevicollis^[15] and consumed by R. punctatus.^[13]

As a pest

In Europe, the blue willow beetle can become a severe herbivore pest on willows.^[16] For plantations of common osier (Salix viminalis), herbivory reducing biomass production by up to 40% has been estimated.^[17] It is susceptible to Bacillus thuringiensis tenebrionis and also Spinosad when treatment is applied to affected plants.^[18]