Silvering on red pepper fruits is a visual defect that can at times become a marketing concern (Photo 1). The defect is not caused by a disease or virus. It often occurs in areas on the fruit that rested against a branch (Photo 2) and appears to be the result of compression or rubbing. However, it can also occur on other parts of the fruit not associated with compression (Photo 3) and the reason for this is not entirely clear. At first glance, it seems to be the result of insect feeding. Thrips are most commonly blamed for causing this silvering on pepper fruit. However, examining the fruit closely under a dissecting microscope, there is no sign of the type of damage that would be caused by thrip feeding.  Early descriptions of thrip feeding inaccurately claimed that they ‘rasp’ or ‘gash’ the plant tissue and then suck up the juices at the surface, but in fact the feeding process by thrips can be best described as ‘piercing-sucking’.  We examined a recent batch of red pepper fruit that came to our office for signs of thrip feeding associated with the silvering, by looking for holes or puncture wounds and did not see evidence of thrip activity. Intact pepper fruit have a uniform cobbled surface (Photo 4). The silvered tissue also has this same texture, but affected cells are bleached of color, but maintain the same uniform cobbled texture (Photos 5 and 6). Other issues on pepper fruit such as cracking (Photo 7) and scarring (Photo 8), are easily distinguished from silvering of pepper fruit.  

The exact cause of silvering of pepper fruit is not clear. As mentioned above, one partial explanation may be a reaction to either compression or rubbing.  Only the very top epidermal cells are affected (Photo 9). As such, it is a minor defect and it is unfortunate that silvering is occasionally the reason for rejection of pepper fruit from the market. 

(Click on pictures to ENLARGE, roll over pictures for CAPTIONS)

7. Cracking of fruit epidermis

8. Scarring on fruit (unknown cause)

9. Cross section showing that just the epidermal cells are bleached

Lygus bug, Lygus hesperus feeding could cause economic damage to celery. Like any other true bug, lygus bug has a piercing and sucking mouth part which appears as a snout-like structure or beak on the head. Within the beak, four stylets are housed which come out while the bug feeds on the plant. In the process, stylets puncture the cells and leave a feeding sheath within the plant (Figure 1a and b). As time progresses, these injured tissues, depending on the severity, turn into sunken or elongated lesions or callus on the stem making the celery unmarketable (Figure 2).

Bagrada bug, Bagrada hilaris (Fig. 1) is an invasive stink bug native to old world countries of southern Africa, Middle East and Asia. It was first detected in Los Angeles County, California in 2008, now well established in Ventura, Los Angeles, Orange, San Bernardino, Riverside, San Diego and Imperial Counties, but recently detected in Santa Barbara and San Luis Obispo Counties. Also, it is a serious pest and has been detected in 4 more states (Arizona, New Mexico, Nevada and Utah) in the U.S.

ATTN: Recently, bagrada bug adults were found on Chinese or napa cabbage in Santa Cruz County.

  Although this bug feeds on a wide range of hosts, we are more concerned because the bug prefers cruciferous hosts (Family: Brassicaceae) including broccoli and cauliflower, which are grown as rotation crops in the Salinas Valley. It is believed that other major crops especially lettuce and spinach are NOT a suitable host for bagrada bug. At the same time, bagrada bug can survive on cruciferous weeds such as mustard species (Brassica sp), wild radish, London rocket, short pod mustard and shepherd’s purse, as well as the insectary crop sweet asylum. Mustard weeds species are very common in the Salinas Valley along ditches, roadsides and even along the edges of agricultural fields. Other species of mustards such as white mustard (Sinapsis alba) and Indian mustard (Brassica juncea) are grown as cover crops. It is clear that given the abundance of mustard family weeds and crops, there is a readily available source of habitat for this insect in the Salinas Valley.

 Bagrada bug adult is often confused with harlequin bug. Adult of harlequin bug is orange with black and white marks, whereas bagrada bug adult is black with orange and white marks; and adult harlequin bug is about 3 times larger than bagrada bug (Fig. 2). Eggs of harlequin bug are white with horizontal, black strips, whereas bagrada bug has no strips but has a “dirty” white appearance.

   It is believed that bagrada bug overwinters as adult in the cracks and crevices in soil or on plants. Generally, female bug is larger in size than male. Eggs are laid on the underside of leaves, cracks and crevices in soil or on hairy stems. There are five nymphal stages for bagrada bug. Typically, bagrada bug is found in aggregation with various nymphal stages and adult rather than individuals (Fig. 3). Because Salinas Valley has relatively mild temperature through year, it is expected that the development of bagrada bug would be prolonged compared with its populations in the warmer regions where it has been established. This also indicates that, if the bug is established, the number of generations of bagrada bug would be fewer in the Valley than in the warmer locations such as southern California or in the desert regions. Normally, its population size is small during early spring to mid-summer but eventually increases in size during later summer or fall.

Damage to host plant is varied but could be severe. Severe economic loss has been reported when injury occurred during early developmental stages of the crop such as coldyledon or < 4 leaves stages. Injury on leaves appears initially as small puncher marks, which turn into white patches as leaves expand (Fig. 4a). In broccoli and cauliflower, the economic injury occurs when the bug feeding kills the apical meristematic tissue of young seedling, which later result in “multiple heads” (Fig. 4b) or sometimes “blind heads” (without a head). Severe feeding also depletes the nutrient reserves of the plant leading to desiccation or wilting.

  At this point, preventing the dispersal of bagrada bug to the Salinas Valley is the key strategy. Growers often move plant materials including transplants to the Valley for production from the regions where the bug has been established. Special care should be given to inspect the plant materials while moving them. Monitoring for bagrada bug during mid-day hours might increase the probability of finding them as the bugs typically hide and stay in the cracks and crevices or on the underside of leaves when the temperature is on the cooler side. Cruciferous weeds in the drains, river bottoms, edges of the field or near residential area increase the risk of establishment. Based on the insecticide efficacy studies conducted in University of Arizona, pyrethroids and neonicotinoids are effective in reducing bagrada bug infestation and injury. For organic growers, none of the products are efficacious but pyrethrin and azidirachtin are suggested.

  If you detect bagrada bug in Monterey, Santa Cruz and San Benito Counties, please do not hesitate to contact me at svjoseph@ucdavis.edu or (831) 759-7359.

For more reading, please visit the links:

http://cisr.ucr.edu/bagrada_bug.html

http://www.plantmanagementnetwork.org/pub/php/brief/2010/bagrada/

http://ucanr.org/blogs/blogcore/postdetail.cfm?postnum=8438

http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=4047