Friday, 24 August 2018

Plant bugs (Aug 23, 2018; Wk 16)

Bugs of the Family Miridae are also referred to by their common name, "plant bugs". Prairie growers are familiar with two plant bugs - lygus and alfalfa plant bugs.  

Plant bugs are a very large group of bugs that can include herbivores, omnivores and predators but virtually all are polyphagous which is a term referring to their ability to feed on several species, even Families of other organisms.  Plant bugs are generally very mobile as both adults and nymphs and move readily to feed on different host plants as the season progresses.  Plant bugs can also have different lifecycles with alfalfa plant bugs reproducing as one generation per year whereas lygus bugs can have two to three generations per year.

This season in southern Alberta, first-generation lygus bugs damaged seed alfalfa in June then the second generation damaged canola fields in July and August. High numbers of lygus bugs (10-20 per sweep and higher) were collected in research and demonstration plots of sainfoin, hemp and quinoa in southern Alberta.  

Both lygus and alfalfa plant bugs have sucking mouthparts and the larger, more mature nymphs plus adults are able to penetrate and extract oils from seeds, causing them to shrivel and lose in quality.  Plant bugs feeding in faba beans can cause spotting.

Wasps in the genus Peristenus include native species that attack lygus and alfalfa plant bugs but normally don't occur in sufficient densities to reduce outbreaking populations of these plant bugs.  The exotic Peristenus digoneutis from Europe, if it could be established and is shown not to interfere with native predators and parasitoids, may increase parasitism to help prevent plant bug outbreaks.  

Adult L. lineolaris (5-6 mm long) (photo: AAFC-Saskatoon).

Fifth instar lygus bug nymph (3-4 mm long) (photo:  AAFC-Saskatoon).