Mirids are a key pest of mungbeans and cotton.
|Scientific name|| |
Green mirid - Creontiades dilutus
Brown mirid - Creontiades pacificus
Crop mirid - Sidnia kinbergi
Green mirid adults are 7 mm long, pale green, often with red markings and have clear wings folded flat on the back. Adults and nymphs are very mobile with antennae nearly as long as the body. Green mirid nymphs have a pear-shaped body and the tips of the antennae are reddish brown.
Brown mirids are similar in shape, but the adults may be slighly larger (8 mm), and the front part of the body is brown instead of green when viewed from the top (i.e. the head and thorax). The nymphs have banded antennae, alternating red-brown and white.
Crop mirid adults are 7 mm long, grey-green on top and bright green underneath. Nymphs are green with brown and white striped antennae and a black spot on the back.
The green mirid is a native species widely distributed across Australia.
The brown mirid has been recorded from northern New South Wales and Queensland. It is distributed in Eastern Asia, including China and Micronesia.
The crop mirid has been reported from all Australian states except the Northern Territory.
|Crops attacked/damage|| |
Mirids are known to feed on cotton, lucerne, mungbeans, navy beans, peanut and soybeans. Green mirids and crop mirids also attack azuki bean
Damage symptoms: Adults and nymphs pierce plant tissue and release a chemical that destroys cells in the feeding zone. In cotton, growing points can be killed resulting in increased branching. Squares, buds, flowers and small bolls can be shed, decreasing yield potential. Boll feeding in cotton can reduce lint yield and quality.
In legume crops, mirids may also attack more mature pods, feeding on and damaging the seeds inside without causing shedding.
|Life cycle and ecology|| |
Mirids feed and develop on a wide range of host plants, including sunflowers, safflower, lucerne and many legumes, and weed species including wild turnips, verbena, common joy weeds and thistles. During the winter months they are often difficult to locate, overwintering as adults or eggs on wild plants in low numbers. However, as temperatures begin to rise in August, their populations increase. The primary movement of mirids into summer crops occurs during November as alternative host plants within the vicinity of cotton crops tend to dry off and insects seek a fresh food source. There is also evidence of long distance migration, possibly from inland areas, associated with weather fronts. This may be the cause of some of the widespread and repeated influxes of mirids sometimes observed in grain and cotton growing regions early in the summer.
Mirid life cycle
Within a crop, mirids lay eggs singly, preferentially on the leaf petiole. The egg is inserted into the plant tissue with an oval egg cap projecting above the leaf or petiole surface. Eggs hatch after 7-10 days depending on temperature; at 30-32º C (average temperature) eggs hatch within 4-5 days and there are five nymphal instars, each of about 2-3 days duration.
Under summer conditions, a generation (egg to adult) can be completed in about three weeks. Adults can live for 3-4 weeks.
Mirid populations may vary significantly with climatic conditions. In sustained hot weather (three consecutive days above 35° C), numbers may decrease. Numbers will also tend to be lower immediately after heavy rains or storms, though early in the season it is thought that storm fronts may also bring influxes of adults. These factors need to be considered when sampling.
|Natural enemies|| |
There are no benenficial species that are recognised to be regulators of mirid populations in cotton. However, damsel bugs , bigeyed bugs , predatory shield bugs , as well as lynx, night stalker and jumping spiders are known to feed on mirid adults, nymphs and eggs.
|Survival strategies|| |
Overwintering habit: Mirids are known to survive on weeds and native host plants in broadacre farming areas. They are also known to breed on native hosts in inland (central) Australia in winter, and can migrate to cropping areas in spring in a similar way to the native budworm, Helicoverpa punctigera. It is thought that this is one of the reasons why insecticide resistance has not been detected, i.e. there is a continual influx of mirids into cropping areas from outside that have never experienced selection pressure for insecticide resistance.
Alternate hosts: Mirids distinctly prefer lucerne to cotton. This has lead some researchers to propose and test the idea of lucerne strips as trap crops to prevent the movement of mirids into cotton crops. To date this practice has not been widely adopted. Other crop hosts include soybeans, mungbeans, pigeon pea, safflower and sunflowers. It is assumed that mirids migrate between these crops. Weed hosts in cropping areas include turnip weed, noogoora burr, variegated thistle and volunteer sunflowers.