Grower Notes and Pest News
Understanding the behavior of a pest is very important in developing appropriate control strategies. Information on feeding, host searching, migratory, and reproductive behavior of the invasive Bagrada bug is very limited in published literature. Since Bagrada bug is a fairly new pest in the United States, there is a lot to learn and understand about this pest. Here is a summary of observations about its feeding and reproductive behavior.
Bagrada bugs are primarily attracted to cruciferous crops. However, the number of host species this pest feeds on or passing through is increasing as it spreads to different parts of California. In addition to various wild and cultivated cruciferous plants, Bagrada bugs have been reported to cause damage to carrots, corn, peppers, potatoes, tomatoes, and sunflower. In an earlier choice study where different host plants were offered, neither adults nor nymphs chose tomatoes when alyssum, broccoli, green bean, and wild mustard were among the choices (Dara and Dara, 2013). However, feedback from some growers this year indicated feeding damage to tomatoes (Dara 2014). Although damage was not confirmed, some growers and homeowners reported finding Bagrada bugs on citrus, fig, grape, and strawberry.
Condition of the plants
During a visit to a home garden a couple of years ago, I noticed several Bagrada bugs on dried branches of wild mustard, although different cruciferous vegetable plants were in the proximity. Considering the ability of Bagrada bugs to move around easily, this observation suggests their preference for certain plant conditions. In a recent visit to a 4-week old broccoli field, Bagrada bugs and their damage was noticed only on small and weak plants. Heavy winds a few weeks earlier affected some plants which were significantly smaller than the rest of the plants and were breaking at the base with a slight touch. Similarly, in my lab colony, several bugs are frequently seen on relatively drier plant material although fresh plant material is also present. All these observations suggest that the concentration of plant juices could be influencing Bagrada bugs choice within a specific host. This could mean that maintaining good health of the plants through optimal irrigation and nutrient management is important to avoid weaker plants that could attract Bagrada bugs.
Bagrada bug nymph on dried wild mustard (Photo by Surendra Dara)
Bagrada bugs were primarily seen on weak and small plants compared to big and healthy plants in the broccoli field
(Photo by Surendra Dara)
Bagrada bugs are known to hide in the cracks of top soil during cooler parts of the day. Even during warmer parts of the day, some bugs were seen in the soil. This behavior could be exploited by the use of entomopathogens such as Beauveria bassiana and Metarhizium brunneum, which are soilborne fungi. Applied through drip irrigation or as a foliar spray, these fungi can be introduced into the Bagrada bug habitat. Natural behavior of the Bagrada bug to dwell in the soil increases its chances of exposure to fungal inoculum. Although solar radiation might inactivate fungal spores on exposed plant surfaces, being soilborne fungi, these pathogens can persist in the soil for longer periods. Preliminary laboratory assays already demonstrated the potential of these fungal pathogens (Dara 2013).
Bagrada bug hiding in the soil (Photo by Surendra Dara)
Based on laboratory observations, Taylor and Bundy (2013) indicated that Bagrada bugs preferred dry soil compared to moist soil to deposit eggs. While this might be the case when Bagrada bugs feed on wild hosts in uncultivated areas, cultivated crops are frequently irrigated and how the soil moisture influences their oviposition behavior in the field conditions is not clear. Earlier literature indicated that eggs are also deposited on various plant parts. Whether eggs are deposited on the plant or in the soil, entomopathogenic fungi could still be important to cause mortality in newly emerged nymphs that might walk on fungal inoculum. If Bagrada bugs overwinter as eggs in the soil, cultivation can be a tool to reduce their numbers. Some entomopathogenic fungi cause egg mortality in addition to infecting mobile stages.
Nature and Numbers
Bagrada bugs have a wide host range and some of their preferred hosts are spread across large areas as wild plants. When these plants dry out, they migrate to crop plants in significant numbers. This is probably why control with pesticide applications alone or using trap crops can be challenging. Some community and home gardeners who tried to use trap crops or traps with alyssum, were able to find large numbers in those crops or traps, but even larger numbers continued to move to crop plants. For a pest like Bagrada bug, exploiting natural enemies appears to be a crucial management tool. Arrangements for foreign exploration of natural enemies are underway.
Dara, S. K. 2013. Bagrada bug update: bioassays and a short video.
Dara, S. K. 2014. Current status of the invasive Bagrada bug in California: geographic distribution and affected host plants.
Dara, S. K. and S. S. Dara. 2013. Bagrada bug host preference: crucifers and green beans.
Taylor, M. and C. S. Bundy. 2013. The life history and seasonal dynamics of Bagrada hilaris in New Mexico. Annual meetings of the Entomological Society of America, Austin, TX.
Adult spotted lanternfly (Lycorma delicatula). Source http://hojae.net/520.
The Pennsylvania Department of Agriculture recently reported the first detection of yet another invasive hemipteran pest in the US. While efforts to have a good grip over other invasive hemipterans like the Asian citrus psyllid, the Bagrada bug, and the brown marmorated stink bug is still underway, there is a new pest that could potentially impact industries ranging from lumber to wine.
An exotic pest known as the spotted lanternfly, Lycorma delicatula (White) was recently detected in Berks County, PA. Spotted lanternfly, which is actually not a fly, but a planthopper is also referred to as “spot clothing wax cicada” or “Chinese blistering cicada” in the literature. It belongs to the family Fulgoridae in the order Hemiptera. Fulgorids or members of the family Fulgoridae are moderate to large planthoppers generally referred to as lanternflies because of the inflated front portion of the head that was thought to be luminous. Spotted lanternfly is regarded as a poisonous insect in Chinese medicine and used for relief from swelling.
Origin and distribution
Spotted lanternfly is native to China and is present in Southeast Asia. It was first reported in South Korea in 2006 and rapidly spread to different parts of the country.
Spotted lanternfly feeds on a variety of host plants including fruit trees, ornamental trees, woody trees, and vines. Apples, birch, cherry, dogwood, grapes, Korean Evodia, lilac, maple, poplar, stone fruits, and tree-of-heaven are among more than 70 species of hosts attacked by this pest. Tree-of-heaven, which contains high concentrations of cytotoxic alkaloids, is one of the favorite hosts. This is probably why spotted lanternfly is considered poisonous and used in traditional Chinese medicine. Other preferred hosts such as Korean Evodia (Bebe tree) are also used in oriental medicine suggesting that spotted lanternfly has a high preference for hosts that contain toxic secondary metabolites. Observations in South Korea also indicate that spotted lanternfly appears to have a wider host range early in life as young nymphs and a narrow range as they grow older, especially before egg laying. Choosing plants with toxic metabolites for egg laying is thought to be a mechanism of defense to protect from natural enemies. Although grape vine does not have toxic metabolites like these other hosts, spotted lanternfly showed a strong preference in studies conducted in South Korea. Sugar content of the host plant also appears to play a role in their choice with a preference for hosts containing high sucrose and fructose content.
Eggs are laid on tree trunks in ootheca (egg case) in groups of 30-50 and are covered in a yellowish brown waxy deposit. Eggs usually hatch during the early hours of the day. Waxy deposit disappears on old egg masses which look like brown seeds. There are four nymphal instars. Nymphs have a black body. The first three instars have white spots while the fourth instar has red wing pads and upper body. Nymphs start climbing up the trees after they emerge and fall off when there is a physical obstacle or disturbance from wind or other factors and start climbing up again. This falling and ascending cycle is thought to be a means of host selection and dispersal. Adult males are 20.5-22 mm (0.81-0.87 inches) long from head to the end of the folded wing and females are 24-26.5 mm (0.94-1.04 inches) long. Forewings are greyish with black spots in different patterns. Part of the hind wing is red with black spots and the rest is white and black. Tips of the wings show a network of veins (reticulated). Abdomen is yellowish with black bands. Legs are black and have white spots during nymphal stages. Length of the legs varies from 15-18 mm (0.59-0.71 inches) in adult males and 18-22 mm (0.71-0.87 inches) in adult females. Adults are weak flyers, but good hoppers. Head is black with piercing and sucking mouthparts. Life cycle is typically univoltine (one generation per year) and spotted lanternfly overwinters as eggs.
Adults and nymphs feed on phloem tissues of foliage and young stems with their piercing and sucking mouthparts and excrete large quantities of liquid. Due to the sugar content of the liquid, plant parts covered with spotted lanternfly excretion harbor mold growth, which could hinder plant growth or even cause death.
Neonicotinoids, pyrethrins, and organophosphates are among the chemical insecticides effective against spotted lanternfly. Adults and 2nd-4th instar nymphs appear to be attracted to spearmint oil which could be used in their control. Using sticky traps at the base of the tree trunks also appears to be a good management strategy. Parasitic wasp, Anastatus orientalis is reported to parasitize up to 69% of spotted lanternfly eggs in China. This egg parasitoid is considered a potential biocontrol agent for release against the spotted lanternfly in South Korea.
Photos of the pest
Pictures of the spotted lanternfly can be found at the following sources:
Fourth instar nymph: https://www.flickr.com/photos/itchydogimages/6984394006/in/pool-lanternbugs
Early instar nymphs: https://www.flickr.com/photos/itchydogimages/6197213287/
Barringer, L. 2014. Pest alert: Spotted lanternfly, Lycorma delicatula (White) (Hemiptera: Fulgoridae). Pennsylvania Department of Agriculture.
Choi, M.-Y., Z.-Q. Yang, X.-Y. Wang, Y.-L. Tang, Z.-R. Hou. 2014. Parasitism rate of egg parasitoid Anastatus orientalis (Hymenoptera: Eupelmidae) on Lycorma delicatula (Hemiptera: Fulgoridae) in China. Korean J. Appl. Entomol. 53: 135-139.
Ding J., Y. Wu, H. Zheng, W. Fu, R. Reardon, and M. Liu. 2006. Assessing potential biological
control of the invasive plant, tree-of-heaven, Ailanthus altissima. Biocontrol Sci. Technol. 16:547-566
Han, J. M., H. Kim, E. J. Lim, S. Lee, Y.-J. Kwon, and S. Cho. 2008. Lycorma delicatula (Hemiptera: Auchenorrhyncha: Fulgoridae: Aphaeninae) finally, but suddenly arrived in Korea. Entomol. Res. 38: 281-286.
Kim, J. G., E.-H. Lee, Y.-M. Seo, and N.-Y. Kim. 2011. Cyclic behavior of Lycorma delicatula (Insecta: Hemiptera: Fulgoridae) on host plants. J. Insect Behav. 24: 423-435.
Frantsevich L., A. Ji, Z. Dai, J. Wang, L. Frantsevich, and S. N. Gorb. 2008. Adhesive properties of the arolium of a lantern-fly, Lycorma delicatula (Auchenorrhyncha, Fulgoridae). J. Insect Physiol 54: 818– 827.
Lee, J.-E., S.-R. Moon, H.-G. Ahn, S.-R. Cho, J.-O. Yang, C. Yoon, and G.-H. Kim. 2009. Feeding behavior of Lycorma delicatula (Hemiptera: Fulgoridae) and response on feeding stimulants of some plants. Korean J. Appl. Entomol. 48: 467-477
Moon. S.-R., S.-R. Cho, J.-W. Jeong, Y.-H. Shin, J.-O. Yang, K.-S. Ahn, C. Yoon, and G.H. Kim. 2011. Attraction response of spot clothing wax cicada, Lycorma delicatula (Hemiptera: Fulgoridae) to spearmint oil. Korean Soc. Appl. Biol. Chem. 54: 558-567./span>
Can entomopathogenic fungus, Beauveria bassiana be used for pest management when fungicides are used for disease management?
Western tarnished plant bug (Lygus hesperus) killed by the entomopathogenic fungus, Beauveria bassiana (Photo by Surendra Dara)
Beneficial fungi such as Beauveria bassiana are pathogenic to insect and mite pests and are commercially available for use in organic and conventional farming. Field studies conducted on commercial strawberry farms with B. bassiana and another entomopathogenic fungus, Metarhizium brunneum show the importance of these microbial pesticides in pest management on conventional farms (Dara 2013, 2014, and unpublished). These studies can make a significant contribution to IPM practices by reducing chemical pesticide use without compromising the pest management efficiency.
In a cropping system where fungicides are frequently applied for managing various foliar diseases such as powdery mildew (caused by Podosphaera aphanis) and botrytis fruit rot (caused by Botrytis cinerea), the fate of a beneficial entomopathogenic fungus is always an important question. Evaluating the compatibility of various fungicides commonly used in strawberries with B. bassiana is necessary to understand the fungicide and beneficial fungus interactions. A series of studies were conducted to address this issue and to explore opportunities to evaluate their compatibility.
In 2012, six bioassays were conducted using fungicides Captan, Elevate, Microthiol Disperss, Pristine Quintec, Rally, and Switch and an organic formulation of B. bassiana (Mycotrol-O) (Dara and Dara, 2013). Mortality and/or infection caused in mealworm (Tenebrio molitor) larvae exposed to surfaces treated with B. bassiana and fungicide was used as a measure of compatibility between the fungicides and the beneficial fungus. Except for Elevate and Quintec, all other fungicides showed moderate to high level of inhibitory effect on the fungus. A follow up study with Pristine showed that increasing the application interval to 1 or 4 days improved the compatibility and resulted in 100% mortality of the mealworms from B. bassiana treatment. Another study was conducted where B. bassiana (BotaniGard EX) was applied 0 to 6 days after fungicides Pristine, Merivon, and Switch were applied (Dara et al. 2014). Switch seemed to have a higher negative impact on B. bassiana than Pristine and Merivon, in general, but the increase or decrease in mealworm mortality with increasing time interval between the fungicides and fungus was variable. Although these two studies indicated that increasing time interval could influence the compatibility of fungicides and B. bassiana,they were conducted only once and warranted additional replicated studies.
A new study was conducted from June to August, 2014 where eight fungicides that had different modes of action were applied at 0 to 6 day intervals to evaluate their impact on mealworm mortality caused by B. bassiana.
Positive control with BotaniGard ES® (B. bassiana)
BotaniGard ES applied 0,1, 2…6 days after treating with Captan.
BotaniGard ES applied 0,1, 2…6 days after treating with Pristine.
BotaniGard ES applied 0,1, 2…6 days after treating with Merivon.
BotaniGard ES applied 0,1, 2…6 days after treating with Microthiol Disperss.
BotaniGard ES applied 0,1, 2…6 days after treating with Rally.
BotaniGard ES applied 0,1, 2…6 days after treating with Rovral.
BotaniGard applied 0,1, 2…6 days after treating with Switch.
BotaniGard ES applied 0,1, 2…6 days after treating with Thiram.
Captan alone applied 0, 1, 2…6 days prior to the exposure.
Pristine alone applied 0, 1, 2…6 days prior to the exposure.
Merivon alone applied 0, 1, 2…6 days prior to the exposure.
Microthiol Disperss alone applied 0, 1, 2…6 days prior to the exposure.
Rally alone applied 0, 1, 2…6 days prior to the exposure.
Rovral alone applied 0, 1, 2…6 days prior to the exposure.
Switch alone applied 0, 1, 2…6 days prior to the exposure.
Thiram alone applied 0, 1, 2…6 days prior to the exposure.
Including the untreated control, there were a total of 114 treatments in each assay. Each treatment had 10 mealworms that were individually incubated in Plexiglas vials with a piece of carrot after a 24 hour exposure to a paper towel treated with B. bassiana, fungicide, or B. bassiana+fungicide applied at different time intervals. Mortality of the worms was observed daily for 6 days. Treatments of fungicides without B. bassiana were also included to see if they have any influence on the mortality of the worms. These assays were repeated three times using medium-sized mealworms purchased from a commercial supplier.
None of the worms in untreated control died during the study. Except for six dead worms out 560 in fungicide only treatments in the first assay, there did not seem to be any impact of fungicides alone on the mortality of mealworms.
Among the fungicides tested, Captan (Mode of action group M4) and Thiram (Mode of action group M3) are the only ones that showed a significant negative impact on B. bassiana resulting in reduced mealworm mortality (Fig. 1, Table 1). Other fungicides had no or negligible impact on B. bassiana. When the average total mortality of the mealworms among different time intervals between B. bassiana and fungicides was considered, Captan caused about 57% reduction and Thiram caused 43% reduction in the efficacy of B. bassiana. Remaining fungicides caused only 0-2% of reduction in the efficacy of B. bassiana. Both Captan and Thiram are broad spectrum fungicide acting through multi-site contact and differ from others, except for Microthiol Disperss (Mode of action group M2), in their modes of action.
Time interval between B. bassiana and different fungicides did not seem to have any impact on the total mortality of mealworms. Although the total mortality caused by B. bassiana ranged from 30-57% in Captan and 33-77% in Thiram treatments at different time intervals, differences were not statistically significant (P > 0.05).
Fig. 1. Average total mortality of mealworms at different time intervals between B. bassiana and fungicides
Table 1. Total mortality caused by B. bassiana when fungicides were applied at different time intervals.
*Means followed by the same letter within each column are not statistically significant (Tukey's HSD P > 0.05). There was no significant difference in values within each row i.e., no difference in time intervals between B. bassiana and any of the fungicides.
This study shows that several of the fungicides commonly used in strawberries are compatible with B. bassiana. When B. bassiana is considered for pest management, Captan and Thiram should be avoided. Fungus-based microbial pesticides play an important role in conventional agriculture and understanding their interaction with fungicides helps with their effective use in pest management.
Dara, S. 2013. Microbial control as an important component of strawberry IPM. February issue of CAPCA's Adviser magazine, pp 29-32.
Dara, S. 2014. New strawberry IPM studies with chemical, botanical, and microbial solutions. February issue of CAPCA Adviser magazine, pp 34-37.
Dara, S. and S.S.R. Dara. 2013. Compatibility of the entomopathogenic fungus, Beauveria bassiana with some fungicides commonly used in strawberries. Strawberries and Vegetables Newsletter (http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=9626)
Dara, S. S., S.S.R. Dara, and S. Dara. 2014. Optimal time intervals for using insect pathogenic Beauveria bassiana with fungicides. Central Coast Agriculture Highlights (http://cesantabarbara.ucanr.edu/newsletters/Central_Coast_Agriculture_Highlights50500.pdf)
Adult light brown apple moth (Photo by Jack Kelly Clark, UC IP)
Nursery workers are our first line of defense in detecting light brown apple moth when growing ornamental plants in commercial nurseries. A new brochure and video can help those in the field distinguish light brown apple moth from several look-alike caterpillars.
Light brown apple moth is currently under a California Department of Food and Agriculture quarantine that regulates the interstate shipment of plants to keep the moth from spreading to new areas. It has been quarantined in various counties throughout coastal California ranging from Mendocino to San Diego.
Light brown apple moth larva (Photo by Jack Kelly Clark)
Correct field identification of the light brown apple moth is the first step in containing the spread of this moth. Unfortunately several other leafroller caterpillars, including the orange tortrix, omnivorous leafroller, avocado leafroller, and apple pandemic moth, look similar to light brown apple moth caterpillars. This makes photo identification tools that can go into the field with workers, like the Field Identification Guide for Light Brown Apple Moth in California Nurseries, a useful resource for nursery workers.
The field guide was created by Steven Tjosvold, Neal Murray, University of California Cooperative Extension; Marc Epstein, Obediah Sage, California Department of Food and Agriculture; and Todd Gilligan, Colorado State University with the Statewide Integrated Pest Management Program (UC IPM).
An exotic and invasive pest from Australia, light brown apple moth has a host range of more than two thousand plants. It is a pest to a wide range of ornamental and agricultural crops, including caneberries, strawberries, citrus, stone fruit, apples, and grapes. The caterpillars eat leaves and buds, leading to weak or disfigured plants. They also can feed directly on fruit, causing the fruit to be unmarketable.
For more information on light brown apple moth and other leafrollers found in nurseries, see the UC Pest Management Guidelines for Floriculture and Nurseries.
Average annual precipitation in California is 200 million acre-feet, out of which 42% of water is used for agriculture while 11% is used in the urban areas (municipal and industrial users) and the remaining 47% by the environment (native vegetation, ground water, and oceans) (Doug Parker, personal communication). According to the National Drought Mitigation Center's Drought Monitor, 95% of California is currently in a severe to exceptional drought condition. Drought has impacted California agriculture in different ways in different regions. Depending on crop needs, geographic location, and availability of ground water, production of each crop is affected in one way or the other. Compared to the Central Valley which is affected most by the drought, agriculture on the Central Coast and Southern California is less affected according to a study conducted by the Center for Watershed Sciences at University of California Davis.
Water use in California (Source: Doug Parker, Director of California Institute for Water Resources and Water Strategic Initiative Leader)
Drought conditions in California as of October 16, 2014. Source: US Drought Monitor.
Some strawberry and vegetable growers in San Luis Obispo and Santa Barbara Counties were contacted recently to assess the current impact of drought. Their feedback helped to put together the following summary of the current status and recommendations to address drought conditions.
Strawberry growers continue to use available groundwater although with concern for future availability. Current impact of the drought on strawberries:
- Strawberries require 21-24 acre inches of water and rainfall accounts for 3-6 acre inches during normal rainfall years. Rainfall leaches salts away from the root zone while meeting irrigation needs. Compared to three years ago, it is estimated that there is up to a 10% increase in some salts, especially calcium and magnesium due to the current drought conditions. This could lead to 5-10% reduction in fruit yields, but severe salt injury could cause higher losses. Additionally, plants would be vulnerable to pests and diseases which could lead to further yield reduction.
- Strawberries are very sensitive to salinity and frequent irrigation is practiced to prevent the accumulation of salts in the root zone. Growers are aware of diminishing groundwater resources and are carefully monitoring water and salinity levels. Extra irrigation to push out salts from the root zone results in nutrient leaching.
- These practices are expected to continue as long as groundwater is available, but acreage could diminish if groundwater becomes unavailable.
Salt injury to strawberry plant (Photo by Surendra Dara)
Strategies to address drought conditions in strawberry production:
- Continue to monitor groundwater levels and provide irrigation to meet water needs as well as to leach out salts.
- Monitor health of plants and regularly scout for pests and diseases which might require more timely treatment actions than usual because plants are already under stress.
- Check nutrient levels in the soil and plant and compensate as needed if irrigation is causing nutrient loss.
- Modify leaching fractions based on salt levels and plant maturity to flush salts away from the root zone.
- Reconsider acreage planted based on groundwater availability to minimize losses.
Vegetable growers are experiencing the impact of drought conditions on their production and are currently relying on available groundwater.
- Water needs for vegetables vary from about 7 to 36 acre inches based on the crop and location. Rainfall during a normal season contributes up to 24 acre inches depending on the crop and season.
- Drought conditions resulted in increased salinity, which has caused 10-20% reduction in yields of some crops and a significant increase in pest and disease pressure. Some growers are managing without any yield losses.
- Some growers have already reduced their acreage by 10% or more while others continue to maintain the current acreage.
- Reducing or completely avoiding pre-irrigation is currently practiced by some growers to cope with water shortage. This practice has also increased salinity in the soil and increased weed populations.
- Some growers have reduced fertilizers or are choosing ones with less salt content.
- In order to monitor salinity and nutrient levels, additional expenses are incurred for water, soil, and plant analysis. Increased weed, pest, and disease problems have also increased management costs.
- Some growers are prepared to reduce acreage up to 25% if drought conditions continue.
Strategies to address drought conditions in vegetable production:
- Continue regular monitoring of groundwater levels, salinity conditions, nutrient status, and provide irrigation and fertilizers as appropriate.
- Regularly monitor for pests and diseases and make timely management decisions.
- Reduce or avoid sprinkler irrigation and use drip irrigation as much as possible.
- Continue to reduce or avoid pre-irrigation to conserve water.
- Modify leaching fractions based on the current salt and crop conditions and administer irrigation as needed.
- Modify acreage to suit future water availability.
My current research is evaluating the potential of entomopathogenic fungi in improving water and nutrient absorption by plants, which could play a role in conserving water resources.
Acknowledgements: Thanks to the strawberry and vegetable growers in San Luis Obispo and Santa Barbara Counties who responded to the survey on drought impact and provided their valuable feedback.
UC and other resources:
California agriculture faces greatest water loss ever – College of Agricultural and Environmental Science, UC Davis
Center for Watershed Sciences - UC Davis
Water use in California – Public Policy Institute of California
California harvest much smaller than normal across crops – The Sacramento Bee
In virtual mega-drought, California avoids defeat – Los Angeles Times