Nysius raphanus Howard Hemiptera Lygaeidae

Natural History

Distribution. The taxonomy of these native insects is not completely resolved, and apparently more than one species is known as false chinch bug. The principal species known as false chinch bug, Nysius niger Baker, occurs throughout most of the United States and southern Canada. Another species, Nysius raphanus Howard, sometimes is common. Most reports in the literature attribute crop damage to Nysius ericae (Schilling), a species found only in Europe, or N. rapha-nus, with which N. niger is easily confused; N. niger is a major pest, despite the confusing reports (Slater and Baranowski, 1978; personal communication with R. M. B). Most reports of damage occur in the southern regions of the United States, particularly the arid southwest and Rocky Mountain regions. However, on occasion false chinch bug can reach high levels of abundance almost anywhere in its range.

Host Plants. False chinch bug has been reported to damage such vegetables as cabbage, carrot, celery, lettuce, mustard, radish, and turnip. Other crops injured include alfalfa, cotton, flax, oats, raspberry, strawberry, sugarbeet, sunflower, tobacco, and wheat. Despite its relatively wide host range, grain crops are not preferred, and damage is infrequent on any crop.

False chinch bug feeds principally on weeds, particularly mustards, and moves to crops when drought or herbivory destroy the preferred hosts. Numerous common weeds are suitable for nymphal development, including Virginia pepperweed, Lepidium virgi-nicum; shepherdspurse, Capsella bursa-pastoris; Russian thistle, Salsola kali; spurge, Euphorbia spp.; and sagebrush, Artemisia tridentata. Sisymbrium irio, a mustard known as London rocket, is especially important in California. Some plants such as carpetweed, Mollugo verticillata; lovegrass, Eragrostis sp.; and blanketflower, Gaillardia pulchella, are reported to be selected as ovi-position sites only during periods of extreme drought (Milliken, 1916).

Natural Enemies. This insect seems to be relatively free from natural enemies, though heavy rain is an important mortality factor.

Life Cycle and Description. The number of generations per year varies with its location and weather. One generation can be completed in about 29 days under favorable weather conditions. In Kansas, five generations are reported annually (Milliken, 1916), whereas 3-5 are observed in Canada (Beirne, 1972). The overwintering stage is variously reported to be the egg, nymph, and adult (Byers, 1973). Burgess and Weegar (1986) reported that eggs could be stored under refrigeration for up to five months, so it is possible that all stages overwinter successfully.

  1. The elongate egg is about 1.5 mm long and 0.4mm wide. It tapers toward both ends. One side is convex, and the opposite side nearly straight. Its color is pinkish white. They may be deposited in loose soil, among bits of organic debris, or among plant parts such as blossoms. The eggs may be laid singly or in small clusters of up to eight. Females produce, on average, one egg per day. Duration of the egg stage is reported to average eight days (range 6-12 days).
  2. There generally are five instars, though instar number has been observed to vary from four to six. The nymphal stages initially are pinkish white, but as they grow they darken to light-brown. Thin, dark longitudinal lines run the length of the body. The body is rather pear-shaped, with the abdomen considerably wider than the thorax. Nymphal development requires about 4, 4, 4, 4, and 5 days, respectively, for instars 1-5 (Milliken, 1918). Thus, total duration of the nymphal stage is about 21 days (range 16-27 days) (Burgess and Weegar, 1986).
  3. The adult is about 3-4 mm long. Because of its general appearance and gregarious habits, it is confused with chinch bug, Blissus leucopterus (Hemiptera:
Insect Pests Crops
False chinch bug nymph.

Lygaeidae). However, in general color the false chinch bug is grayish-brown to blackish brown, bearing transparent wings marked with rows of small spots. In contrast, chinch bug is generally black, and marked with a large dark spot on each of the front wings. In food habits they also differs markedly. Chinch bug prefers grain and grass crops, but false chinch bug prefers broadleafed crops. The adult false chinch bugs commonly aggregate, both for feeding (Milliken, 1916) and mating (Byers, 1973). They begin egg production about 16 days after reaching maturity, and may survive for up to seven weeks. Mass dispersal is often observed, probably in search of food.

A description of false chinch bug was given by Riley (1873). The major observations on biology were reported by Milliken (1916, 1918). Rearing techniques were developed by Burgess and Weegar (1986). False chinch bug was included in the key by Slater and Baranowski (1978).

IKf/j

Adult false chinch bug.

Damage

These weed-feeding insects cause injury when they disperse, often in tremendous numbers, to nearby crop plants. Wene (1958), for example, described population densities of 5 per sq cm on vegetables in Texas. Because of their small size they often escape notice, and it is not until plants wilt that the insects are observed. They also move on and off the plant in response to weather, often seeking shelter beneath clods of soil during the heat of the day and at night (Leigh, 1961). Margins of fields are especially affected. The rapid wilting and death of plant tissue, especially following feeding by nymphs, caused Barnes (1970) to suggest that a toxin might be present in the saliva of this bug; this has not been investigated. Tappan (1970) described injury on several plants as minute necrotic lesions surrounded by chlorotic tissue. False chinch bug feeding on seed disrupts seed formation and inhibits seed germination (Wood and Starks, 1972). This insect also is capable of transmitting Nema-tospora coryli, a yeast pathogen of mustard (Burgess et al, 1983).

Management

  1. Careful visual inspection of weeds, particularly cruciferous species, surrounding fields is suggested during periods of drought. During the warmest portion of the day it is advisable to examine sheltered areas, such as lower surfaces of foliage and beneath soil clods, for aggregations of bugs. False chinch bug tends to be highly aggregated in distribution, so systematic inspection is required. A sampling technology has been developed in Canada for adult Nysius niger that probably works for N. raphanus, also. Pivnick et al. (1991) successfully tested a yellow trap that used mustard oils (isothiocyanates) as a lure.
  2. False chinch bug is controlled with foliar applications of insecticides. False chinch bug is not generally considered to be difficult to control, but not all insecticides work equally well. Owing to the irregular appearance of the insect, preventative applications should be made only if high densities be found on nearby weeds, and an ideal scenario would be to control the insects on the weeds before they disperse. Dispersal into crops is more likely to occur during periods of drought. Invasion of crops can sometimes be stopped with border treatments only, as the bugs usually disperse by walking rather than flying.

Cultural Practices. Weed management is especially critical for this insect. For example, in California large populations build up on London rocket during the spring. Nymphs and adults disperse to crops when this mustard is depleted by feeding, or the weeds are tilled. To avoid crop damage, weeds could be destroyed before insect populations develop to high levels, or perhaps the weeds could be killed at a time when crops susceptible to injury were not available (Barnes, 1970).

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