SEARCH

SEARCH BY CITATION

Keywords:

  • Apocynum androsaemifolium ;
  • biological control;
  • dogbane beetle;
  • non-target impacts;
  • Vaccinium angustifolium

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Insect pest management in wild blueberry (Vaccinium angustifolium Aiton) usually involves insecticidal sprays, which may have detrimental effects on non-target beneficial insects. Dogbane beetle (Chrysochus auratus Fabricius) (Coleoptera: Chrysomelidae) feeds almost exclusively on spreading dogbane (Apocynum androsaemifolium L.), an increasing weed problem in wild blueberry production. Because C. auratus is an important natural enemy of spreading dogbane, we assessed its susceptibility to several insecticides it may be exposed to during insect pest management. In laboratory bioassays, we found adult dogbane beetles were highly susceptible to field rates of phosmet (Imidan) and acetamiprid (Assail) by direct topical contact and ingestion of treated foliage, whereas no mortality was seen with spirotetramat (Movento) and chlorantraniliprole (Altacor). Topical applications of spinetoram (Delegate) did not cause significant mortality of beetles, but high mortality to beetles was found when they ingested spinetoram-treated foliage. The results suggest that while some insecticides used in blueberry management will be hazardous to C. auratus, options are available that will cause little harm to this natural enemy.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Wild blueberry (Vaccinium angustifolium Aiton, syn. ‘lowbush’ blueberry) (Ericaceae) is an important crop in eastern Canada and the state of Maine in the United States (Robichaud 2006). In Canada, wild blueberries are commercially grown on over 55 000 ha of land at an average value exceeding $86 million per year (AAFC 2012). Growers often must concurrently manage insect pests, weeds and diseases, and this is usually carried out with chemical pesticides. However, because expanding markets for blueberries have increasingly stringent pesticide residue restrictions (Anonymous 2008; EU 2013), there is a desire and need to reduce chemical inputs and increase use of non-chemical control options. Conservation of natural enemies that are already in the blueberry agroecosystem could alleviate the need for persistent pesticide use.

Spreading dogbane (Apocynum androsaemifolium L.) (Apocynaceae) is an important weed in wild blueberry fields (Boyd and Hughes 2011; Wu and Boyd 2012). It spreads by seed and rhizomes and is difficult to control once established. Herbicides used to control spreading dogbane are broad spectrum and can be harmful to the crop (Boyd and Hughes 2011). The dogbane beetle, Chrysochus auratus Fabricius (Coleoptera, Chrysomelidae), is a holarctic species found throughout eastern North America (Arnett et al. 2002). It feeds almost exclusively on dogbane plants (Apocynaceae), especially Indian hemp (Apocynum cannabinum L.) and spreading dogbane (Dobler and Farrell 1999; Peterson et al. 2005; MacEachern 2012). In Nova Scotia, overwintered eggs hatch in spring, and larvae feed on roots. Adults typically emerge in late June and are present until late August (MacEachern 2012). At high densities, dogbane beetles can consume up to 40% of spreading dogbane foliage (MacEachern 2012).

A number of insecticides may be applied mid-summer by blueberry producers for control of blueberry maggot fly (Rhagoletis mendax Curran) and, more recently, spotted-wing Drosophila [Drosophila suzukii (Matsumura)]. Because most of the insecticide spray would be intercepted by the plant canopy before reaching the ground, exposure of soil-dwelling dogbane beetle larvae would be unlikely. However, dogbane beetle adults may very well be exposed to foliar sprays of insecticides. Thus, the objective of this study was to examine the susceptibility of dogbane beetle adults to several pesticides they may potentially be exposed to during insect pest management in wild blueberry.

Materials and Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Spirotetramat (Movento® 240SC; Bayer CropScience, Calgary, AB, Canada), acetamiprid (Assail® 70WP; E.I. Dupont, Mississauga, ON, Canada), spinetoram (Delegate™ WG; Dow AgroSciences, Calgary, AB, Canada), chlorantraniliprole (Altacor®; E.I. Dupont) and phosmet (Imidan® 50WP; Gowan Co., Yuma, AZ) were used in experiments. Treatments for various experiments reflected high and low field concentrations based on a spray volume of 200 l/ha. These were as follows: spirotetramat at 0.34 or 0.27 g active ingredient (AI)/l; acetamiprid at 0.56 or 0.48 g AI/l; spinetoram at 0.25 or 0.13 g AI/l; chlorantraniliprole at 0.50 or 0.38 g AI/l; and phosmet at 2.25 or 1.13 g AI/l. Treatment solutions were prepared in deionized water containing 0.015% Tween (Sigma-Aldrich, Oakville, ON, Canada). Based on availability of field-collected beetles, bioassays were initiated on 11 July and 20 July 2012.

Dogbane beetle adults and spreading dogbane ramets were collected from a wild blueberry field in Oxford, Nova Scotia (45o45′17″ N, 36o49′35″ W). The field had not been treated with insecticide prior to insect collection that year. Beetles were picked off dogbane plants by hand, placed in plastic containers with spreading dogbane foliage, transported back to the laboratory and stored at 4°C for 1–2 days until experiments were initiated. Additional spreading dogbane ramets were put in containers separate from beetles and when returned to the laboratory, stems were immediately stored at 4°C in a refrigerator.

Beetles were exposed to insecticides by either direct topical contact or foliar ingestion bioassays. For contact bioassays, beetles were cooled for ~5 min in a refrigerator and then placed in a 10-cm-diameter glass Petri dish and sprayed with 1 ml of treatment in a spray tower. Control beetles were sprayed with deionized water containing 0.015% Tween. Treated beetles were then placed in 475-ml polystyrene cups containing a spreading dogbane ramet (~15 cm) that was inserted into a floral water pick (Sproule Enterprises Inc., Mississauga, ON, Canada) containing tap water. Cups were covered with a 10-cm-diameter glass Petri dish.

In foliar ingestion bioassays, ~10-cm-long stems of spreading dogbane ramets were dipped in insecticide or 0.015% Tween solution for ~5 s and dried at room temperature for 1–2 h on wire racks. Each stem was then inserted into a floral water pick and placed in a 475-ml polystyrene cup. Beetles were placed on the foliage, and each cup was then covered with a 10-cm glass Petri dish.

For all bioassays, there were three replicate cups per treatment, each containing five beetles, and mortality was determined after 48 h. A Kruskal–Wallis test was used to compare beetle mortality among treatments (SAS 2010).

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Chlorantraniliprole and spinetoram did not adversely affect adult dogbane beetles when exposed by topical contact (χ2 = 5.52, df = 6, P = 0.24; data not shown), but spinetoram caused high mortality to beetles when ingested (χ2 = 17.19, df = 6, P = 0.009) (fig. 1a). Exposure to acetamiprid and phosmet had a strong effect on dogbane beetle survival when administered topically (χ2 = 19.54, df = 6, P < 0.003) (fig. 1b) and orally (χ2 = 19.54, df = 6, P < 0.003) (fig. 1c). Spirotetramat and chlorantraniliprole did not adversely affect beetle survival through either exposure route. Despite our relatively small sample sizes, the large effect size and low standard deviation in responses (fig. 1) resulted in high statistical power (1.0) in all analyses (SAS 2010).

image

Figure 1. Susceptibility of dogbane beetle, Chrysochus auratus, adults (n = 5) to high (grey bars) and low (black bars) field rates of acetamiprid (Assail), phosmet (Imidan), spinetoram (Delegate), spirotetramat (Movento) and chlorantraniliprole (Altacor) in foliar ingestion (a, c) and direct contact (b) bioassays.

Download figure to PowerPoint

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Dogbane beetle is endemic to eastern North America and can be a useful natural enemy of spreading dogbane (MacEachern 2012), an important weed for blueberry growers (Wu and Boyd 2012; Wu et al. 2013). However, the occurrence of adult beetles often coincides with that of important insect pests that are controlled with pesticide sprays. We found that dogbane beetle adults varied in their acute susceptibility to various insecticides registered for use in wild blueberry.

As expected, beetles were highly susceptible by direct contact and ingestion to field rates of the organophosphorus insecticide phosmet and the neonicotinoid insecticide acetamiprid. Insecticides from of these classes have activity against a wide range of insects, and phosmet and acetamiprid can be used to manage pests in family Chrysomelidae, such as the Colorado potato beetle (Bishop and Grafius 1991; French et al. 1992; Elbert et al. 2008). Phosmet and acetamiprid are prominently used for management of blueberry maggot fly (Delbridge et al. 2013). Harmful effects would probably occur in dogbane beetles subjected to incidental exposure of these products during sprays against blueberry maggot in mid-late July, although field tests would be required to confirm this.

Spinetoram is registered as a control for blueberry spanworm [Itame argillacearia (Packard)] and blueberry flea beetle (Altica sylvia Malloch) (Delbridge et al. 2013). Although spinetoram is effective against Coleoptera (Biondi et al. 2012) and is used against blueberry flea beetle, application of spinetoram would likely occur before the emergence of dogbane beetle adults in late June. Moreover, spinetoram was non-toxic by direct contact, and there was some survival of dogbane beetles that ingested foliage treated with the lowest rate of spinetoram. Given that our laboratory study represents a worst-case exposure scenario, additional field studies are warranted to evaluate the risk of spinetoram applications to dogbane beetle in wild blueberry production.

In contrast to effects seen with phosmet, acetamiprid and spinetoram, spirotetramat and chlorantraniliprole had no impact on dogbane beetles. Spirotetramat has recently been registered for use against blueberry maggot fly – against which it demonstrates good efficacy (G.C.C., unpublished data) – and blueberry gall midge (Dasineura oxycoccana Johnson) on wild blueberries, and chlorantraniliprole against blueberry spanworm [Itame argillacearia (Packard)] and red-striped fireworm (Aroga trialbamaculella Chambers) (Delbridge et al. 2013). We did not expect to see effects of spirotetramat on dogbane beetle because it is a tetramic acid lipid biosynthesis inhibitor that specifically targets sucking insects like aphids, mealy bugs and white flies (Maus 2008). In other studies, spirotetramat exposure had relatively low impact on lady bird beetles and other beneficial insects, making it a useful option for IPM (Schnorbach et al. 2008). Likewise, chlorantraniliprole is an anthranilic diamide insecticide (ryanodine receptor agonist) that is targeted against Lepidoptera larvae. Our laboratory results represent a worst-case exposure scenario and suggest that applications of spirotetramat and chlorantraniliprole in wild blueberry fields under realistic conditions would pose minimal hazard to exposed dogbane beetles.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

We thank the Wild Blueberry Producers Association of Nova Scotia and the Natural Sciences and Engineering Research Council (NSERC) of Canada for financial support, and Bragg Lumber Co. for field access.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References