The cereal leaf beetle (Oulema melanopus) is a significant crop pest, described by Carl Linnaeus in 1758.

Adults feed before winter and spend most of their overwintering time in protected areas such as wind rows, crop stubble, and tree bark crevices.

It has a defense mechanism in which it smears excrement on its body to mask its vibrant color and deter predators.

[1][2][3][9][10][12] Adults, on average, are about 5 mm long and have dark-blue wing covers and red legs.

[14][19] O. melanopus consumes nearly all cereal crops, but has a strong affinity for oats, barley, and rye, and its favorite host is wheat.

[5][10][20] The physical symptoms of the plant caused by them are thin, long lines where the upper epidermis of the leaf has been eaten.

Most likely, a secondary compound in barley incites an eating response, perhaps when a lack of desired food is present.

[6] Scientists have had success in labs with a few types of nematode, Steinernema feltiae B30, S. carpocapsae C101, and Hetero-rhabditis bacteriophora D54.

Since the spread of O. melanopus is so great, a consistently important factor to consider is the temperature when selecting which strain is the most effective for the desired location.

[10] Another biological control consists of larval parasites; Diaparsis carnifer, Lemophagus curtis, and Tetrastichus julis are wasps that do this [10] D. carnifer and L. curtis both consume the O. melanopus larvae, and T. julis lays eggs inside of the body of the O. melanopus larvae.

Specifically, T. julis does not seem to pose too much risk to the crops themselves, but is extremely effective at dispatching large populations, around 90%.

It is a good control agent because it is hearty and its lifecycle is synchronous with that of O. melanopus, the disadvantage being that it is not host-specific, and can cause other unforeseen deaths in other bugs, disrupting the balance of the ecosystem.

[10] Even without human intervention, O. melanopus has experienced a decline in the United States due to general weather conditions such as drought or excessive rainfall.

Meissle et al. found that mortality of O. melanopus on Cry3Bb1 transgenic maize was double that of the wild type.

In one experiment, four pesticides belonging to two groups (organophosphates and pyrethroids) were tested to see their effects on the beetles' numbers.