Mortality of Metarhizium anisopliae -infected wireworms (Coleoptera: Elateridae) and feeding on wheat seedlings are affected by wireworm weight

2011·1.6 MB·English

by  Willem G Van Herk

1
38 J.Entomol.Soc.Brit.Columbia108,December201
SCIENTIFIC NOTE
Mortality ofMetarhizium anisopliae-infected wireworms
(Coleoptera: Elateridae) and feeding on wheat seedlings are
affected by wireworm weight
WILLEM G. VAN HERRi and ROBERT S. VERNON^
As some wireworm species are notorious seed) placed inside. Only mobile wireworms,
pests of common wheat, Triticum aestivum appearing healthy (Vernon et al. 2008) and
(Vernon et al. 2009), a small study was actively feeding 2 to 3 d prior to placement in
conducted at the Pacific Agri-Food Research the containers were used for this study.
Centre (PARC) in Agassiz, BC in August Wireworms selected ranged considerably in
2009, to determine whether the number of weight (range: 6.6 to 46.4 mg; Table 1), but all
germinating wheat seedlings (cv. AC Barrie) wireworms in individual containers were
killed by the dusky wireworm, Agriotes similar in weight (within 5.0 mg), and an
obscurus, is affected by the number and size attempt was made to have an equal number of
of the wireworms that seedlings are exposed similar sized wireworms for each ofthe 1, 2,
to. An unexpected factor appeared at the end and 3 or 4 wireworm densities to determine
of the study in that many wireworms were the effect ofwireworm weight on the number
infected with Metarhizium anisopliae, ofwheat seedlings killed.
resulting in considerable mortality. This factor Two days after wireworms were placed in
precluded us from meeting some ofthe initial containers, 21 untreated wheat seeds were
objectives ofthe experiment, but still allowed planted 2 cm deep in small pre-made holes.
us to determine if mortality of seedlings was Seeds were spaced at equal distance (1.75 cm)
affectedbywirewormweight andnumber, aMnd from each other, in a 3, 5, 5, 5, 3-grid pattern.
if mortality of the wireworms from Afterplanting, groups ofeight containers were
anisopliae infection was affected by their placed in 26 cm x 47 cm x 6 cm deep nursery
weight. flats (Eddi's Wholesale Garden Supplies, Ltd.,
We filled 160 500 ml circular (dia= 11 cm, Surrey, BC), 1.01 cold water added between
height = 8 cm) plastic containers (Plastipak the containers in the flat, and flats covered
Industries, Inc., La Prairie, QC) with 500.0 with 14 cm high transparent plastic domes
(+/- 0.2) g of soil collected from a field at (Eddi's Wholesale) to prevent desiccation of
PARC, Agassiz in 2009. The soil was sieved the upper layer of soil. After planting,
mm mm
through a 2 x 2 screen to remove containers were subjectedto a 12:12 light:dark
rocks and organic material, made up to 20% regimen.
moisture by weight, and homogenized. Seedling emergence was first observed 5 d
Containers with soil were placed in a walk-in after planting, stand counts were conducted 8
cooler set at 15.0 +/-0.5°C to mimic soil d (when domes were permanently removed
temperature conditions in spring when wheat due to the length of plant shoots) and 15 d
is normallyplanted. Wireworms were weighed after planting. Wireworms were removed 25 d
individually on August 7, and 0-4 wireworms after planting and their health evaluated
were placed in each container (Table 1). All (Vernon et al. 2008). This revealed that only
wireworms were collected at PARC in April 123 of255 larvae were alive, the rest having
2009 and stored in 401 Rubbermaid tubs died from Metarhizium infection, most likely
without food, at 8-10°C, until 1 wk before the within the first two weeks of the study as
study, when tubs were brought up to room evident from the extent ofmould formation on
temperature and food baits (a cup of 100 ml the surface of the cadavers. Analysis of the
moist vermiculite mixed with 10 ml wheat proportion of wireworms dead in each
^ PacificAgriFoodResearchCentre,AgricultureandAgriFoodCanada, P.O. Box 1000,VOM lAO,Agassiz, British
Columbia,Canada
1
J.Entomol.Soc.Brit.Columbia108,December201 39
Table 1.
Proportion ofwheat seedlings dead ornot emerging 15 days afterplanting. N ^ numberofcontainers.
Shown are least squares means and SE estimates calculatedfromANCOVA; all least squares means are
significantly different from 0 at P<0.0001. Numbers followed by different letters in columns are
significantly different fromeach otheratP<0.05, using aTukey-Krameradjustment.
wireNwo.oromfs in N wWeiigrhetwroarnmge wirMeowdoerlms1:pAllalced N Model 2: Surviving
wireworms alone
container (mg) in containers
0 43 0.084(0.018)A 80 0.113 (0.009)A
1 43 6.6-46.4 0.101(0.012)A 50 0.151 (0.012)AB
2 36 8.6-42.3 0.166 (0.013) B 21 0.202 (0.018) BC
3 iz ZJ.6 - 4J./ J U.z4o (U.U3/j dL-
4 26 8.2-41.3 0.250 (0.014) C 4 0.313 (0.041) C
ANCOVA F=1.18,df-19,135, F-0.97, df=19,135,
Flat:
P=0.28 P-0.50
F=25.15,df=4,135, F=11.51,df-4,135,
Statistics No. ofwireworms:
P<0.0001 P<0.0001
F=0.51,df=l,135, F-16.78,df=l,135,
Wireworm weight:
P=0.47 P<0.0001
container with ANCOVA (PROC GLM, SAS weight per container (Table 1, Model 1).
9.1) with variable container flat and covariate Treating the number of wirewonns in the
average wireworm weight in containers, container as a variable allowed us to calculate
indicated that flat did not have a significant least squares means for the proportion of
effect (F=0.91, df=19,96, P-0.57), but seedlings killed per wirew^orm density, and
wireworm weight did (F=14.r7, df=l,96, produced a similar model as when both
P=0.0003). Eliminating the variable flat from wireworm number and average weight were
the analysis and regressing the proportion of included as covariates. The second analysis
wireworms dead to the average wirewomi was similar, differing only in that the number
weight in each container produced the of wireworms that survived was included.
following model: Proportion dead - 0.107 + Both models indicated that the flat in which
0.015 X wireworm weight (SE = 0.099, 0.004; containers were placed did not have a
t=1.08, 4.42; P=0.28, <0.0001, respectively; significant effect on plant mortality (P>0.05;
model = 0.145), indicating that the Table 1), and that the number ofwireworms in
proportion ofwireworms dead increased with the container was highly significant
the average weight of wireworms in the (P<0.0001), with the proportion of plants
container. killed increasing with wireworm number
Considering the mortality of wireworms (Table 1). The weight of wireworms in the
during the experiment, two separate analyses container did not appear to significantly affect
were conducted to determine the effect of the number of plants killed if all wireworms
wireworm number and weight on wheat placed in each container were considered.
seedling survival. In the first analysis, the However, as heavier wireworms were more
proportion of wheat seedlings that did not likely to die from Metarhizium, and mortality
emerge by 15 d after planting was evaluated appeared to have occurred early in the study
with ANCOVA, with variables flat and the when the wheat plants were most susceptible
number ofwireworms originally placed in the to wireworm attack, this is probably a
container, andthe covariate average wireworm misleading conclusion. When only surviving
1
40 J.Entomol.Soc.Brit.Columbia108,December201
wireworms are included in the analysis (Table apparently not been observed in wireworms
1, Model 2), it is apparent that heavier before, and should be confirmed and
wireworms caused more damage than smaller explained with further study. As Metarhizium
ones. While this confirms the expectation that is commonly present in Agassiz soil, all
larger wireworms are more destructive to locally collected larvae likely contain spores
wheat seedlings than smaller ones, the finding and an environmental trigger (e.g. temporary
that larger wireworms are more likely to die exposure to a high temperature) necessary to
from Metarhizium than smaller wireworms is induce infection. Considering the LT50 ofA.
novel and of importance, as it suggests that obscurus after Metarhizium infection, the
using the fungus as a biological control agent infection seen here was likely triggered prior
forwireworms maybe more effective for later to wireworm placement in containers
than earlier instars. This relationship has (KabalukandEricsson 2007).
ACKNOWLEDGEMENTS
We thank our summer students, Selina Harding for helping collect and weigh
McGinnis, Heike Kosterke, and Chantelle wireworms andplantwheat seeds.
REFERENCES
Kabaluk, J. T, and J. D. Ericsson. 2007. Environmental andbehavioral constraints on the infection ofwireworms
byMetarhiziumanisopliae. EnvironmentalEntomology36: 1415-1420.
Vernon,R.S., vanHerk,W.,Tolman,J., Saavedra, H.O., Clodius, M., andB. Gage. 2008. Transitionalsublethaland
lethal effects of insecticides after dermal exposures to five economic species of wireworms (Coleoptera:
Elateridae). JournalofEconomicEntomology 101: 365-374.
Vernon, R.S.,vanHerk,W., Clodius,M.,andC. Harding. 2009. WirewormmanagementI: Standprotectionversus
wirewormmortalitywithwheatseedtreatments. JournalofEconomicEntomology 102: 2126-2136.