A Comparison of Pyrethrum Fogging and Screen-sweep Netting of Micro-Hymenoptera in Southern California Chaparral

2007·6.8 MB·English

by  Alex R Van Dam

HYM. RES.
J.
Vol. 16(1), 2007, pp. 192-205
A Comparison of Pyrethrum Fogging and Screen-sweep Netting of
Micro-Hymenoptera in Southern California Chaparral
Alex R. Van Dam, Matthew H. Van Dam, and John M. Heraty
CA
Department of Entomology, University of California, Riverside 92521, USA; email:
(AVD) [email protected]; (MVD) [email protected]; (JMH) [email protected]
—
Abstract. Three chaparral plant species, Adenostoma fasciculatum Hook, and Arn. (Rosaceae),
Ceanothus megacarpus Nutt. (Rhamnaceae) and Quercus bcrbcridifolia Liebm. (Fagaceae), were
sampled for micro-Hymenoptera in the Santa Rosa Plateau Nature Reserve in Southern California.
Two sampling methods of the shrub's canopy are contrasted: screen-sweep netting and pyrethrum
fogging. Using both sampling methods and across all of the plant hosts, 242 species of
Hymenoptera were collected. A total of558 individuals and 173 species were collected by fogging,
and 287 individuals and 115 species by screen sweeping. Although fogging captured more
individuals and species, results were significant only for the number of individuals collected on
Quercus and number of species on Adenostoma. On the three different plants, fogging sampled
a similar or greater number of species than did screen sweeping. In terms of estimating species
richness, fogging had an equivalent or greater efficiency than sweeping for collecting individuals
and species. Whencombined with thelaborefficiency involved inprocessing field samples, fogging
is superior toscreen sweeping. However, given the sample sizeswithin this study, both techniques
are necessary, with the fogging technique sampling only 71.5% of the total number of species of
Hymenoptera.
Hymenoptera are one of the most di- Many of these parasitoids are small,
verse groups of insects, with approximate- usually ranging in size from 1-5 mm, and
ly 115,000 described species and 300,000 to difficult to collect except with specialized
2.5 million undescribed species (LaSalle methods (Noyes 1982, Noyes 1989). Vari-
and Gauld 1992, 1993, Gauld and Gaston ous authors have attempted to evaluate the
1995, Stork 1988, Grissell 1999). Based on best methods to sample these micro-Hy-
conservative estimates, more than 10 per- menoptera with an emphasis on both
cent of all insect species are parasitoids, numbers of individuals and species (Mas-
and approximately 75% of these are Hy- ner and Goulet 1981, Darling and Packer
menoptera (Eggleton & Belshaw 1992). 1988, Noyes 1982, Noyes 1989, Buffington
Recent estimates for Chalcidoidea alone and Redak 1998).
estimate 357,000-400,000 species, of which Many studies have compared collecting
only about 22,000 have been described techniques for Hymenoptera in tropical
(Noyes 1978, Noyes 2000, Heraty and and temperate ecological regions (Hender-
Gates 2003). Parasitic Hymenoptera are son and Whitaker 1977, Noyes 1989,
valuable to agriculture as biological control Gadagkar et al. 1990, Erwin 1995, Hill
agents (Van Driesche and Bellows 1996) and Cermak 1997, Longino and Colwell
and to conservation as a means of measur- 1997, Stork and Hammond 1997, Hoback et
ingbiodiversityand a potential indicatorof al. 1999, Yanoviak 2003), but little has been
the diversity of lower trophic levels (Kre- written about sampling in the short, dense,
men et al. 1993, Heraty and Gates 2003). scrub vegetation that is typical of Mediter-
Volume 16, Number 1, 2007 193
ranean climate zones. Use of an "Allen and a limited amount of debris, but only
Vac" in a coastal sage scrub plant commu- the latter can be used to selectively sample
nity in Southern California produced more specific plant hosts, as explained herein,
individuals and a higher diversity of Canopy fogging techniques were re-
Hymenoptera than did sweep netting, viewed by Erwin (1989), who noted that
and was considered more effective because such techniques allow for sampling of
insects were sampled from deeper within tropical and temperate forest canopies
the shrub canopy than possible for a sweep more effectively than with other methods
net (Buffington and Redak 1998). The such as sweep netting. Problems with
primary disadvantage ofvacuum sampling fogging in a tree canopy include collecting
is the damage caused to small, fragile insects outside of the sampling area, drift
parasitic Hymenoptera, which can make of specimens from within the sampling
identifications difficult. Another important area, and the need to collect at dawn, when
aspect for choosing a particular method is there is no breeze, but perhaps less insect
the amount of time spent sorting through activity (Erwin 1989, Stork and Hammond
the accumulated debris to find specimens 1997). Importantly, insects are collected
(Southwood 1978). The efficiency of vacu- somewhat randomly and can be sampled
um sampling is counterbalanced by the in replicated samples for a specific area
labor necessary to sort specimens from the (Stork and Hammond 1997). Insecticide
accumulated debris collected along with fogging can also be applied to collecting
the specimens. Unfortunately, sweep net- insects on rough or inaccessible surfaces
ting and the direct aspiration of minute such as tree trunks (C. Burwell, pers.
specimens is probably the least efficient comm.) or vertical rock faces (S.B. Peck,
method of sampling - many specimens pers. comm). In a chaparral vegetation
may simply escape during collection, avoid community, the issue is not whether
detection in the accumulated plant debris, sweeping can reach the upper canopy,
or may not be sampled if they are not but whether sweeping can efficiently and
readily accessible by the net. Adding thoroughly sample insects from within the
a metal screen to the net opening to interior of the 'canopy' of dense, often
exclude debris (Noyes 1982) can increase thorny, bushes. Insecticide fogging of this
the efficiencyoffinding specimens,butthis miniature tree canopy has a potential for
can result in greater damage to the speci- sampling a different array of insects in
mens, and the efficiency of processing will both numbers and species than would be
depend on whether specimens are aspirat- sampled by beating the exterior of the
ed (maximizing loss of specimens) or if the shrub with an insectnet. Canopy fogging is
entire sample of specimens and plant also an easily quantifiable method since
debris is collected into alcohol and later a known surface area ofcatch basins can be
sorted in the laboratory (maximizing pro- put underneath the canopy being fogged,
cessing time). To improve the quality of Canopy fogging in chaparral ecosystems
specimens and reduce the time spent might also produce samples that are free of
sorting, new methods for rapid assessment debris or damage unlike screen-sweep
of Hymenoptera populations, and espe- netting. Another attribute of fogging is that
daily micro-Hymenoptera, in dense cano- it allows for the collection of specimens
pysituations are needed. Possiblesolutions from individual plant species like screen-
include passive collecting techniques such sweep netting. In this paper we hope to test
as Malaise trapping (indirect method), pan theefficacyofpyrethrum foggingcompared
trapping (indirect), or insecticide fogging to screen-sweep netting in a chaparral
techniques (direct method). These tech- ecosystem in Southern California for col-
niques yield fewer damaged specimens lecting parasitic micro-Hymenoptera.
194 Journalof Hymenoptera Research
Fig. 1. Foggingmethod used tocollect Hymenoptera from a Quercusberberidifoliabush inSouthernCalifornia.
MATERIALS AND METHODS open and held closed by a twist tie that
—
Location and date. Sampling took place could be removed to empty the contents
on the two dates July 11, 2001 and July 18, into a 1-quart plastic Ziploc® bag contain-
2001 at 3 adjacent sites in the Santa Rosa ing 80% EtOH. The contents of the Ziploc®
Nature Preserve, in Riverside County, bag were rinsed with additional 80% EtOH
California, at 33 31'N 117'14'W and to kill and preserve the insects. Each bush
590 m elevation. We chose 3 similar stands was swept over all its of the surfaces by
of dense chaparral over a 5-acre area: one a single collector (John Pinto, UCR) to keep
stand adjacent to a field of endemic bunch the sampling as uniform as possible.
grass, the second adjacent to a road bor- Sampling of all 3 sites took about 45 min
dered by invasive grass, and the third in on each dat—e.
the heart of a dense stand of chaparral. We Fogging. The insecticide fogging of
used both fogging and screen sweeping to shrubs required several steps on the two
collect from 3 individual bushes from 3 dates. First, 36 yellow Dixie® bowls (total
dominant plant species on two dates: area = 1 m2) were placed underneath the
Adenostoma fasciculatum Hook, and Arn. canopy of each bush to be sampled. Each
(Rosaceae), Ceanothus megacarpus Nutt. bush was sprayed with Raid Yard Guard®
(Rhamnaceae), and Quercus berberidifolia for 1 min from a distance of about 1.5 m,
Liebm. (Fagaceae).— enveloping the bush in a fine fog with no
Screen-sweeping. We used a triangular visible droplets on the leaves (Fig. 1).
net hoop with 38-cm sides and a recessed Approximately one spray can (473 ml;
covering of 6.4-mm hardware cloth to 16 fl oz) was used for 3 bushes. After
exclude large debris. The sweep net was 5 minutes, pans were emptied and rinsed
a fine-meshed net bag from Bioquip (Gar- with 80% EtOH into one gallon plastic
dena, CA), with the apex of the net bag Ziploc® bags. Fogging took approximately
Volume 16, Number 1, 2007 195
2 hours to complete from setup to finish et al. 2003), the number of individuals in
for all 3 sites. The air movement was the two higher taxonomic groups (Chalci-
minimal during sampling periods and doidea and non-Chalcidoidea) and families
was not considered to have impacted of Hymenoptera (Tables 1-3).
specimen drift. — The ecological modeling program Esti-
Processing samples. Two strainers with mates version 7.0 (Colwell 2004) was used
square mesh openings of 3.2 and 1.6 mm to compare the two methods for species
were used to separate the screen-sweep richness (Figs 1-3) and similarity of shared
samples into course, medium and fine species (Table 4) forChalcidoidea and non-
debris samples. Because of the lack of Chalcidoid micro-Hymenoptera by plant
debris, fogging samples were directly species. The diversity settings for Esti-
sorted without screening. Each sample mates 7.0 were set to sample with re-
was sorted with use of an llxll-cm Rose placement and the number of replications
Entomology® sorting tray with parallel set to 1,000 to calculate the Chaol richness
sorting lanes separated by raised ridges estimator (Chao 1984), Sobs estimator
13-mm apart. To ensure that all specimens (Colwell 2004) and singletons estimator
were discovered in the samples, each tray (Chazdon et al. 1998, Colwell and Cod-
was sorted twice, and in some screen- dington 1994) (Figs 2-7). The advantage of
sweep samples three times. Specimens estimating the diversity by selection of
were transferred to small glass vials and samples with replacement is that estimator
then dried for mounting by use of the variance remains meaningful at the right
Hexamethyldisilizane (HMDS) technique hand end of the accumulation curve, and
(Heraty and Hawks 1998) and then card thus can be used to compare data sets
mounted (Noyes 1982). All mounted speci- (Colwell 2004). Scatter plots of these
mens were individually labeled with col- estimator values of species were plotted
lection information and a unique specimen against the estimated number of individu-
identifier number. Data were input into als observed in pooled quadrat samples to
a Filemaker® database for the UCR Ento- construct models (Figs 2-7). The Chaol
mology Research Museum, where all ma- species estimator is used for the sampling
terial was deposited. All Hymenoptera history of species represented by at least
were identified to family, genus, and two individuals (Magurran 2004). The Sobs
morphological species groups using avail- estimator estimates sampling of the mean
able identification keys. Certain groups number of new species collected among
were identified, or our identifications the samples (Colwell 2004). The Singletons
verified, by other local specialists at UCR: estimator estimates sampling of the mean
Mymaridae identified by Serguei Triapit- numberofnew species represented onlyby
syn, Trichogrammatidae by John Pinto, one individual (Colwell and Coddington
Pteromalidae and Eulophidae by Roger 1994), and thus is a rough estimate of the
Burks, Signiphoridae by James Munro, number of rare species. Accumulation
Figitidae by Matthew Buffington, and curves from each of these estimators >:^n
Aphelinidae by J—ung-Wook Kim. be used to compare the relative efficiency
Data analysis. ANOVA analysis re- of fogging and screen sweeping in captur-
vealed no significant difference in speci- ing species diversity (Figs 2-7).
mens collected between sampling dates A Morisita-Horn species similarity index
(p<0.05), so we pooled the data for the was calculated with use of standard de-
remaining analysis. A 2-tailed Student's t- fault settings of Estimates to compare
test was used to compare the number of the number of shared species collected on
individuals collected by fogging and their respective plant species with fogging
sweep netting for each family (MendenhaU and screen sweeping after correcting for
Journalof Hymenoptera Research
196
U3
(J
01
bo
C
0e1
ai
OJ
in
o
60
g
'3d
o
X
a
u
_oj
'oo
en
a;
'G
0)
eon
-a
c
01
Oh
o
C
01
i
x
o
T3
0>
u
_OI
"o
d
c
-a
c
re
O6)0
f3
w
Volume 16, Number 1, 2007 197
Table2. Numberofspeciescollected byeachsamplingmethod (pooled)andaveragenumberofindividuals
(x ± SE) ofChalcidoidea sampled at the Santa Rosa Reserve.
Numberofspecies \tt\mno.ofindi\idu.iU
Fogging Sweeping Both logging Sweeping
Aphelinidae 13
Adenostoma 0.90 ± 0.20* (16)
Ceanothns 0.61 ± 0.23* (11)
Quercus 1.28 ± 0.40* (23)
Chalcididae
Adenostoma
Ceanothus
Quercus
Encyrtidae 23
Adenostoma
Ceanothus
Quercus
Eulophidae 29 25
Adenostoma
Ceanothus
Quercus
Eupelmidae
Adenostoma
Ceanothus
Quercus
Eurytomidae
Adenostoma
Ceanothus
Quercus
Mymaridae 11
Adenostoma
Ceanothus
Quercus
Ormyridae
Adenostoma
Ceanothus
Quercus
Pteromalidae 14
Adenostoma
Ceanothus
Quercus
Signiphoridae
Adenostoma
Ceanothus
Quercus
Torymidae
Adenostoma
Ceanothus
Quercus
Trichogrammmatidae
Adenostoma
Ceanothus
Quercus
Chalcidoidea 92 56 38
Adenostoma
Ceanothus
Quercus
198 Journalof Hymenoptera Research
Table3. Numberofspeciescollectedbyeachsamplingmethod (pooled)andaveragenumberofindividuals
(x + SE) ofnon-chalcidoid Hymenoptera sampled at the Santa Rosa Reserve.
Numberofspecies Meanno.ofindividuals
Fogging Sweeping Both Fogging Sweeping
Bethylidae
Adenostoma
Ceanothus 0.06 ± 0.06 (1)
Quercus 0.17 ± 0.09* (3) 0*
Braconidae
Adenostoma 0.33 ± 0.19* (6) 0*
Ceanothus 0.50 ± 0.22 (9) 0.06 ± 0.06 (1)
Quercus 0.33 ± 0.14* (6) 0*
Ceraphronidae
Adenostoma 0.44 ± 0.18 (8) 0.39 ± 0.16 (7)
Ceanothus 0.06 ± 0.06 (1) 0.06 ± 0.06 (1)
Quercus 0.17 ± 0.12 (3) 0.06 ± 0.06 (1)
Crabronidae
11
Adenostoma
Ceanothus
Quercus 0.06 ± 0.06 (1)
Figitidae
Adenostoma
Ceanothus
Quercus 0.17 ± 0.09 (3) 0.06 ± 0.06 (1)
Diapriidae
Adenostoma
Ceanothus
Quercus 0.06 ± 0.06 (1)
Dryinidae
Adenostoma 0.11 ± 0.08 (2)
Ceanothus
Quercus
Formicidae
Adenostoma 0.56 ± 0.17* (10) 0*
Ceanothus 0.44 ± 0.15* (8) 0*
Quercus 1.28 ± 0.39 (23) 0.78 ± 0.13 (14)
Ichneumonidae
Adenostoma
Ceanothus
Quercus 0.06 ± 0.06 (1)
Platygastridae
Adenostoma 0.06 ± 0.06 (1) 0.28 ± 0.18 (5)
Ceanothus 0.06 ± 0.06 (1)
Quercus 0.11 ± 0.08 (2) 0.33 ± 0.20 (6)
Scelionidae
Adenostoma 2.00 ± 0.46 (36) 1.50 ± 0.41 (27)
Ceanothus 1.00 ± 0.30* (18) 0.27 ±0.11* (5)
Quercus 1.77 ± 0.55* (32) 0.50 ± 0.12* (9)
Sphecidae
Adenostoma 0.06 ± 0.06 (1)
Ceanothus 0.11 ± 0.08 (2)
Quercus
non-chalcidoid Hymenoptera 35 13
Adenostoma 3.56 ± 0.51 (64) 2.17 ± 0.58 (39)
Ceanothus 2.06 ± 0.35* (37) 0.56 ± 0.15* (10)
Quercus 4.17 ± 1.00* (75) 1.72 ± 0.34* (31)
Volume 16, Number 1, 2007 199
Chalcidoidea non-Chalcidoidea
70 30 mum
60
25-I
50
(A {{'fcfrffii W 20 -L _ n-O
<O0D) 40 DOan QO) 15
S>5 Q. 30 Q.
CO ,n 0)
8 20 10
oooooooooo jOO-OO-OOO-OO-Oo
10-
20 40 60 80 100 10 20 30 40 50 60
Individuals Individuals
70
60
50
w JpSHffi
0S5 0) 40
u
a) DO
Q. 30
20
3 ^OOOOOOOOOO °o°oooooooo
10 20 30 40 50 60 70 80 90 10 20 30 40
Individuals Individuals
80n
70
60
Journalof Hymenoptera Research
200
Table 4. Morisita-Horn indices for shared species
of micro-Hymenoptera collected at the Santa Rosa
PlateauReservebycanopyfoggingandscreennetting
by planthost.
Volume 16, Number 1, 2007 201
ble 4). However, especially for Chalcidoi- ton) accumulated at a slightly faster rate in
dea, screen sweeping collected a large most of the fogging samples (Figs 2-A, 7),
number of unique specimens (56) despite but were roughly the same for the Ceano-
the low sample size. thus non-Chalcidoidea (Fig. 5) and Quercus
Of the three estimators, Chaol provides Chalcidoidea (Fig. 6). Only the non-Chal-
an indication of the ability to sample the cidoid micro-Hymenoptera on Adenostema
species thoroughly (more than two indi- (Fig. 5) demonstrated a decline in the
viduals of each species sampled), Sobs number of singletons, suggesting overall
focuses on the accumulation of new spe- that the maximum number of species had
cies, and the singletons estimator is the been sampled even though the species
accumulation of species based only on accumulation curves (Chaol and Sobs)
a single specimen. Only the singletons had not yet reached a plateau.
estimator is expected to decline as a habitat
is more thoroughly sampled and species DISCUSSION
are shifted to the Chaol category. The Insecticide fogging of tree canopies has
Chaol and Sobs estimates should both been experimented with since the late
plateau as the number of species becomes 1960's (Martin 1966, Gange and Martin
thoroughly sampled. In all cases, estimates 1968, Roberts 1973, Erwin and Scott 1980,
for fogging were consistently based on Erwin 1983, Adis et al. 1984, Stork and
a sample with greater number of individ- Hammond 1997). Typical canopy fogging
uals (Figs 2-7; Table 1). Results for the in the tropics is used to access the forest
Chaol estimator species accumulation canopy 30-60 m above the ground (Erwin
curve had the number of 'common' species 1983, Stork and Hammond 1997). Here we
both accumulate and also reach a plateau suggest that the canopy of dense thorny
at a significantly faster rate using the shrubs in chaparral habitat can present
fogging technique for most of the data some of the same problems of sampling,
partitions (Figs 2-4, 7), whereas screen but on a much smaller scale. The fogging
sweeping accumulated common species at strategy employed in this paper has
a faster rate for non-Chalcidoidea on a number of advantages in: 1) relying
Ceanothus (Fig. 5) and Chalcidoids on upon compact and inexpensive equipment
Quercus (Fig. 6). In these latter two cases, that can be carried easily to the field, 2)
fogging still sampled more species overall the sampling area can be defined by the
on Quercus (71 versus 56), whereas the collecting surface under the plant, 3)
same number of species of non-Chalcidoi- a specific bush or species of plant can be
dea (11) were sampled on Ceanothus and in targeted, 4) debris is minimized and the
neither case did the number of species specimens can be quickly and efficiently
appear to plateau (Figs 5, 6; Table 1). Thus processed, 5) there is very minimal, if any,
fogging will generally sample the highest damage to specimens, and 6) there is no
and best represented diversity of common damage to the plants being sampled,
species with the leasteffort, asbased on the which may be a factor in some conserva-
number of specimens collected. The mean tion studies. Our method draws many
number of new species accumulated (Sobs parallels with the typical tropical forest
estimate) was virtually the same for Chal- canopy fogging as in Stork and Hammond
cidoidea using both methods (Figs 2, 4, 6), (1997), and faces similar issues of speci-
and for the non-Chalcidoid micro-Hyme- men drift within and outside of the
noptera, slightly higher on Ceanothus sampling area, but on a less dramatic
(Fig. 5) or lower on Adenostema and Quer- scale. Climatic conditions (i.e. wind) re-
cus (Figs 3, 7). The number of species mains an important factor, but can be
represented by a single specimen (single- monitored and controlled throughout the