The Lygus Bug - A Problem for Greenhouse Pepper and Cucumber Growers

Table of Contents

1. Description
2. Damage to Plants
3. Immigration into Greenhouse Crops

Description

The Lygus bug (Figure 1) or tarnished plant bug is a problem that pepper and cucumber growers have to address annually. Lygus bugs overwinter as adults in sheltered areas, such as leaf litter, under bark, etc., and usually begin emerging from these sites around mid-April to early May to seek out food and mates. Eggs are laid in young tissue where they incubate for a period of 10-20 days. The hatched immatures or nymphs (Figure 2) pass through five stages, and new generation adults appear after about 30-45 days. Adults live for 1-2 months. Presence of overwintered adults overlap with the new generation adults for several weeks, but numbers of the new generation are greater. The number of generations produced in southern Ontario is about three with each female being able to produce about 100-300 eggs during its 5-7 weeks lifetime. Because overwintered adults often do not resemble new generation adults in colour and form, overwintered adults are often considered a different species by the casual observer. In overwintering Lygus adults, colour patterns are generally broader and more intense in the males than in the corresponding females, and the males are larger and more elongate than the females. The intensity and extent of the colour pattern, and differences between males and females, are probably influenced by temperature, humidity, sunlight, host plant, and age of the individuals. However, a survey carried out by researchers from Agriculture Canada and the University of Guelph during 1997-1998, determined that the predominant, and perhaps only important species in Ontario is Lygus lineolaris.

Figure 1. Adult Lygus lineolaris

Figure 2. Lygus nymph.

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Damage to Plants

All species of Lygus are mainly plant feeders and thrive on a very wide range of host plants including many commercially-grown flowers, fruit trees, garden, forage, and field crops, small fruits, forest tree nurseries, and weeds. Lygus bugs have a particular preference for young developing tissue and as such, their damage in peppers is often manifested by development of multiple shoots, distortion of flowers and young fruits (Figure 3), and shedding of floral buds. Damage caused by these bugs in cucumbers could include destruction of the growing point of young seedlings and "ragging" of leaves which appear crinkled and may have several holes (Figure 4). Malformations resulting from feeding by Lygus bugs are considered by some researchers to be caused by the following:

1. feeding on rapidly growing young tissues;
2. mechanical destruction of growing tissues by the insect's mouth parts;
3. chemical destruction of cells by salivary enzymes produced by the bugs;
4. inhibition of growth of the injured part by substances induced by feeding of the bugs;
5. promotion of growth in surrounding tissues by plant growth-promoting substances in the bug's saliva.
   

Figure 4. Lygus damage on cucumber.

Immigration into Greenhouse Crops

Immigration of post-diapausing Lygus bugs into greenhouse crops occurs annually during spring. This is especially problematic in operations that have drastically reduced pesticide use because of reliance on biological controls as a major pest management strategy. However, anecdotal reports indicate that high populations of Orius insidiosus in greenhouse pepper operations are associated with suppression of Lygus bug populations.

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