Campylomma (Mullein plant bug)

Life history

Campylomma overwinters as an egg, which is inserted deeply into the tissue of a woody host plant. Eggs hatch in the spring, beginning as early as tight cluster to pink stage of tree development and continuing through petal fall. Egg hatch peaks during or shortly after bloom. Nymphs pass through five instars. The total period of nymphal development depends on temperature and takes about 21 days at 72ºF.

Nymphs from the overwintering eggs may be present from mid-April to mid-June in central Washington. Adults first appear in mid- to late May. Studies of campylomma colonies on a herbaceous host showed females lived an average of 17 days and laid an average of 38 eggs. Eggs hatch in 7 to 13 days at constant temperatures between 68 and 81ºF. On apple and pear, the highest densities are usually detected in the spring, with minor peaks throughout the rest of the year. The majority of the campylomma population spends the summer on herbaceous hosts, especially mullein, so samples taken in tree fruits represent only a part of the population. In summer, campylomma feed on insects (primarily thrips) and on the host plant. In late August, adults begin migrating back to woody hosts, such as apple and pear, where they mate and lay overwintering eggs through October. Observations indicate 2 to 4 generations occur annually in the Pacific Northwest.

Damage

Campylomma is one of the few tree fruit pests in the Pacific Northwest that is also a predator. Throughout most of its distribution in Europe and Asia no fruit damage has been noted, and it has been reported as an important predator of mites and occasionally aphids. In the Pacific Northwest, it preys on aphids and pear psylla and can greatly enhance biological control of these species. However, for a relatively short period around bloom, it feeds on flower parts and developing fruitlets. Although fruit feeding may occur later than this period, it does not seem to cause damage. Early feeding causes a reaction in the fruit, producing a dark, raised, corky wart, often surrounded by a shallow depression . Feeding punctures can occur individually, or an entire quadrant of the fruit may be damaged. Multiple stings on a fruit usually cause some degree of fruit deformity. Stings tend to be more visible on the skin of Golden Delicious than on darker colored cultivars, and the scars may be a lighter tan color.

Monitoring

Campylomma may be sampled using several methods, depending on the stage and time of year. One of the most critical periods for sampling is before and during the bloom period, when a control decision should be made. Either a beating tray or direct visual examination can be used at this time. The beating tray takes less time to cover an area, but direct examination may reveal nymphs that are not jarred from the foliage using a beating tray. It is estimated that about 70% of the nymphs are recovered using the beating tray method.

A standard beating tray is an 18-inch square piece of cloth stretched tautly on a wood or aluminum frame. A circular tray with a surface area of 324 square inches (a diameter of about 20.3 in) can also be used. The tray is placed beneath a limb with abundant foliage and flower clusters, and the limb is struck sharply three times with a length of thick rubber hose or cushioned wood. This is referred to as a tap sample. During the early season, a black cloth surface on the beating tray can make the translucent nymphs more visible. The accumulated pollen and debris that fall on the tray should be brushed or shaken off after each sample, and the surface should be washed when stains start to interfere with the ability to detect campylomma.

Action thresholds for campylomma are currently tied to the tap sample method. Action thresholds developed for British Columbia are an average of 1 nymph per tap for Golden Delicious and 4 nymphs per tap for Delicious. A sequential sampling plan was also developed under British Columbia conditions. Because the distribution of campylomma is aggregated, or clustered, a fairly high number of taps is needed to estimate the population with accuracy. Although neither the sampling plan nor the action thresholds have been validated under Washington conditions, they provide a good starting point. Note that this sampling plan was developed for 0.5 hectare (1.2 acre) blocks only. Realistically, any block of trees that are of the same age and managed similarly must suffice. If the block contains mixed cultivars, the most sensitive cultivar should be sampled. A fixed sample of 20 taps per block has been recommended in the past in absence of good statistical information. Although not precise, it will provide a rough estimate of the campylomma population.

In summer, when campylomma are most likely to be in or around aphid colonies, direct examination of the aphid infested terminals is probably the most efficient means of sampling. Both adults and nymphs can be monitored with either the beating tray or visual examination. Since no damage is known to occur during this time, there are no action thresholds.

In the fall, adults migrating back to orchards can be sampled with pheromone traps. A wing-type trap with spacers between the trap top and bottom is the most effective. Pheromone traps may be useful in separating orchards into risk categories so that sampling the following spring can be prioritized in high risk orchards.

Biological Control

Biological control of campylomma may be difficult, since it is itself a predator. There are currently no reported natural enemies of campylomma that would be useful in a commercial situation.

Management

The first step in management must be to determine if a damaging population is present in the orchard. Damage the previous season has not always been a reliable indicator of damage to the current season’s crop, although it is advisable to sample those orchards where high levels of fruit damage occurred in the past. Some insecticides applied at delayed-dormant stage may kill early hatching campylomma nymphs. Thus, it is possible that several negative samples be taken before and during early bloom but, when residues of the delayed dormant application wear off, nymphs may be suddenly found in what was thought to be a clean orchard. If temperatures are warm during the pre-bloom period and tree development is rapid, or if there are few overwintering eggs, the delayed-dormant application may provide sufficient control. However, when cool weather extends the period from delayed-dormant to petal fall, or the number of overwintering eggs is high, an application targeted specifically for campylomma may be necessary. It is advisable to take repeated samples throughout the pink to petal fall period if no decision is reached. Spray timing is the key factor in preventing damage by campylomma. Petal fall sprays may fail to prevent much of the potential damage, even though they may kill the campylomma present. Pre-bloom and bloom sprays have been more successful in preventing fruit damage. Choice of materials at bloom is restricted to those that are less toxic to bees (see section on Honeybee). Most of the materials effective on campylomma are Class 1 bee toxicants and cannot be used during bloom. There may be some potential for cultural or behavioral controls for campylomma. Removing the summer hosts, such as mullein, may reduce potential campylomma problems. High campylomma populations in spring have been associated with high aphid populations the previous late summer and fall, when campylomma adults are laying overwintering eggs.