Efficient Release Strategies for Aphid Natural Enemies in Flower Crops 1996 proposal
into Flower Crops
Many arthropods are serious pests of floricultural crops produced in
the US. Current control measures for these pests fundamentally depend on
the prophylactic use of insecticides, resulting in more insecticide applications
to floricultural crops than to any other crop. While this practice is understandable
in view of the explosive population growth exhibited by arthropods and
the aesthetic damage resulting from their feeeding, this repeated heavy
use of insecticides is clearly inconsistent with integrated pest management,
a concern for the environment, and a concern for the health and safety
of agricultural workers. The use of regular releases of commercially available
natural enemies can be an effective alternative to insecticide-based control
in experimental trials. However, the substantially higher direct cost associated
with biological control compared to conventional insecticide control has
hindered its widespread acceptance as a practical method of pest control.
Several methods have been proposed to reduce the cost of biological
control; and while these techniques have provided some economic relief,
none of them have reduced the cost structure to levels generally accepted
by greenhouse growers. The long range goal of my project is to develop
effective and practical biological pest management programs for flower
crops presently using aphids as a model system.
During the first year of the project funded by the Endowment (the 1995
CY), I rigorously documented: (1) the spatial dynamics of aphid outbreaks
in potted chrysanthemums, (2) density-dependent growth rates of aphid subpopulations,
and (3) compared the abilities of two commercially available aphid natural
enemies, the parasitic was Aphidius colemani and the aphid predator Chrysoperla
carnea, to locate aphid infested chrysanthemums within the greenhouse.
The importance of these advances to chrysanthemum growers and to the development
of efficient releases of natural enemies are: (1) an understanding of how
aphid outbreaks progress through a chrysanthemum greeenhouse and how control
measures may be tailored to these patterns, (2) determination of maximum
aphid densities and growth rates beyond which biological control measures
are impractical, and (3) to progress toward understanding how natural enemies
may be released in the most efficient manner to bring about effective and
economical biological control.
During the 1996/97 fiscal year, I will evaluate the ability of several
natural enemies to control aphid outbreaks in chrysanthemum greenhouses
utilizing release strategies based upon aphid distributions and natural
enemy behavior, I will study the role of naturally occuring variation in
aphid susceptibility in chrysanthemums on biological control, and I will
conduct trials in commercial greenhouses to compare the efficacy of each
release strategy and selection of least susceptible cultivars in producing
successful and cost effective biological control of aphids. The methods
developed from this research should be applicable for natural enemy releases
targeted at other pests of floricultural crops.
Introduction and Literature Review
The research outlined in this proposal represents a continuation of
the multiyear project originally funded by the Endowment in 1995. Because
my original proposal detailed work to be completed over a three year period,
I will provide brief summaries of the past year’s accomplishments and concentrate
on objectives for fiscal year 1996/97. Aphids (esp. the green peach aphid,
Myzus persicae, and the melon aphid, Aphis gossypii) are some of the most
serious pests of greenhouse floricultural crops. Difficulty in controlling
these pests may be due to the development of insecticide resistance or
the development of superior biotypes or races. Hence, complete reliance
on chemical control is a risky proposition. Under the optimal conditions
of the greenhouse environment, aphid population growth can be explosive.
Aphid young are born fully formed and are able to feed immediately. They
grow rapidly, and because normal sexual reproduction is not required, eggs
can start developing within an aphid when or before it is born. By the
time a female matures, several young are fully developed in her reproductive
system and are ready to be born at a rate of 3 to 6 a day for several weeks.
Aphids damage crops directly, wilting and distorting leaves and flowers
as they feed, but they also cause a number of other problems. The simple
physical presence of aphids often reduces the aesthetic value of many flower
crops. The honeydew excreted by aphids as they feed promotes the growth
of black sooty molds, which in turn reduces photosynthetic ability and
aesthetic value. Dust, dirt, and skins shed in molting adhere to the viscous
substance, making plants unsightly. Furthermore, aphids transmit several
plant viruses. Because most floricultural crops have little tolerance for
damage, growers must identify pest populations early and take appropriate
control measures. The need for early control has resulted in the sometimes
unnecessary prophylactic use of chemicals for aphid control in greenhouses.
The repeated heavy use of insecticides is clearly inconsistent with integrated
pest management, a concern for the environment, and a concern for the health
and safety of agricultural workers.
Biological control utilizing repeated releases of large numbers of predators
and parasitoids, has been extremely effective for pest control across a
variety of pest-crop systems 5,6 8,12. Regardless, the 3-10 fold difference
in the monetary costs typically associated with implementing biological
control compared to conventional insecticide practices prevents most growers
from embracing it as a regular practice. As a response to this economic
problem, many researchers continue to search for natural enemies that may
be more effective than their present counterparts in hopes that a more
effective natural enemy will reduce costs. One result of this approach
is an increased knowledge of many aphid natural enemies exhibiting potential
to provide control under greenhouse conditions. These natural enemies include
Aphidolefes apidimyza (the aphid midge), Aphidius matricarie, (and other
aphid parasites), Chrysoperla carnea (the green lacewing), and Verticillium
lecanii (a fungal pathogen).
While this ’shotgun’ approach may eventually be successful, it has
yet proven to provide a methodology for the development of effective biological
control programs for pests of greenhouses or floricultural crops.
I propose an alternative to this perpetual search process. I propose
that at least one of the currently available natural enemies will be economical
and effective if it is optimally produced and utilized. My approach to
this problem is to address (1) how mass-rearing practices may be modified
to reduce producer costs and maximize natural enemy quality which will
ultimately reduce costs to the growers, (2) how releases strategies may
be modified to achieve the best possible level of control for a specific
number of natural enemies released, and (3) how effective and grower-friendly
monitoring tools can be used in implementing biologically and economically
cost-effective control measures.
Funding for the first facet of my approach has been solicited from the
National Biological Control Institute, with full support from the Association
of Natural Biocontrol Producers and the USDA-APHIS Biological Control Laboratory.
The third facet has received 1 -year of funding from the Texas Integrated
Pest Management Program. The generous financial support provided by the
Endowment, together with the support provided by Yoder Bros. (for donating
rooted chrysanthemum cuttings), Bunting Biological North America (for providing
parasitic wasps), and Buena Biosystems (for providing predators), have
facilitated my recent advances in developing efficient release strategies
to bring about aphid biological control.
In the studies described below, I have chosen to concentrate on C. carnea
and Aphidius colemani for several reasons.
(1) C carnea is readily available and relatively inexpensive ($2-3
per 1,000) from numerous US insectaries 9.
(2) Biological control of green peach aphids infesting potted chrysanthemums
has been demonstrated using releases of C carnea.
(3) A comparative study of several aphid parasitoids discovered that
A. colemani parasitized significantly more green peach and melon aphids
than did A. matricariae and Lysiphlebus lestaceipes 19.
Based on this result, it was concluded that A. colemani may be the most
suitable species for use in aphid control. Previous findings support the
need to study C carnea biology more thoroughly in order to develop effective
biological control strategies. Based on results from these studies, it
was concluded that at least four releases of lacewings at the rate of 1
predator to 50 aphids were needed to provide satisfactory control 15. In
addition, if there were four or fewer aphids per plant, these were not
discovered by the searching predator and no control was achieved. It was
estimated that I st instar lacewings search an area no more than 6 inches
from the release site suggesting that predator movement patterns, plant
spacing and predator release strategies are essential components to controlling
aphid populations. In addition, the best control was achieved on dense
bushy plants suggesting that plant architecture also influences the outcome
of the biological control program.
Laboratory studies demonstrate the potential for achieving biological
control of green peach and melon aphid infesting greenhouse crops with
releases of parasitic wasps 9. In these studies, host suitability of the
melon, chrysanthemum (Macrosiphum euphorbiae), and green peach aphid for
the parasitoids A. code, A. matricariae, and L. lestaceipes were tested.
In these petri dish tests, none of the parasitoids successfully parasitized
chrysanthemum aphids. A. colemani parasitized 80% of the melon aphids and
57% of the green peach aphids. A. matricariae parasitized 43% and 7% and
L. testaceilms parasitized 27% and 7% of the melon and green peach aphids,
respectively.
Objectives and Anticipated Benefits
The cost structure associated with natural enemy releases prohibits
widespread acceptance of this practice by greenhouse growers even though
releases of natural enemies are a feasible substitution for the use of
conventional insecticides.
Several techniques have been examined to narrow the financial gap between
biological and chemical control. These techniques include: (1) release
of the minimal number of natural enemies necessary to effect biological
control, (2) optimization of mass-rearing programs to minimize the cost
associated with natural enemy purchases 4. 16 , and (3) release of only
the most effective natural enemies. A fourth mechanism that has not been
explored in as much detail is the method in which the natural enemies are
released, and how release methodology may be influenced by variation in
aphid susceptibility among chrysanthemum cultivars. The project outlined
in this proposal addresses these last two aspects with the anticipated
benefit that it will (i) quantify aphid resistance already present in commercial
chrysanthemum cultivars, (ii) lead to successful and cost effective biological
control of aphids, and (iii) identify circumstances whereby attempts at
implementing biological control will be biologically and economically hopeless.
In addition, the method should be applicable for natural enemy releases
targeted at other pests of floricultural crops. I have avoided the use
of banker plants and pest-in-first strategies since these methods frequently
release into the greenhouse a pest species in addition to the target natural
enemy. These methods have not been embraced by growers attempting to produce
a crop free of insect damage.
Specific Objectives:
1. Assess How Natural Enemies May Be Optimally Utilized in Greenhouses
Characterized by Variation in the Spatial Distribution and Densities of
Aphids. Upon completion of this objective, I will (1) know how spatial
distributions of aphid outbreaks influence natural enemy foraging behavior,
(2) comprehend foraging behavior under the most realistic situations as
possible, and (3) measure the impact of natural enemies on aphid outbreaks
in chrysanthemum.
2. Determine Efficacy of Natural Enemies Once They Have Located an Aphid-Infested
Chrysanthemum Plant. Completion of this objective will provide knowledge
of natural enemy foraging behaviors after they have located an infested
plant. Combining this study with Objective I will provide knowledge of
natural enemy behavior among as well as within plants. Putting these components
together with our previous knowledge (from 1995 AFE funded research) of
aphid distributions and aphid population dynamics we will identify appropriate
release rates and release distributions believed necessary for effective
biological control.
3. Identify the Importance of Existing Variation in Aphid Resistance
within Chrysanthemum to Aphid Biological Control. The occurrence of multiple
chrysanthemum cultivars within production greenhouses is standard practice
within the industry. Completion of this objective will aid growers in the
selection and spatial arrangement of existing aphid susceptible and resistant
cultivars in a manner that will improve aphid management programs.
4. Conduct Trials in Commercial Greenhouses to Test the Efficacy of
Release Strategies. Tests will be conducted in greenhouses provided by
commercial cooperators (Ellison’s Greenhouses, Brenham, TX and Lone Star
Growers, San Antonio, TX) to evaluate the dependence of successful biological
control on the spatial distribution and timing of natural enemy release
points. Providing a useful pest management tool to the greenhouse and floriculture
industries is the goal of this project too.
Material and Methods
Objective 1. In this study, I will assess:
(1) how spatial distributions of aphid outbreaks influence natural
enemy foraging behavior. By altering aphid distributions and natural enemy
release distributions, I will assess how modification of these parameters
influences the ability of wasps to locate aphid infested plants.
(2) Document natural enemy aggregation under the most realistic situations
possible. Here I will test whether aphid parasitoids aggregate to aphid
infested patches, the rate at which they locate and aggregate to localized
infestations, and whether aggregation is influenced by aphid distributions.
(3) Measure natural enemy rates of attack on aphids infesting chrysanthemum
and thus quantify the ability of natural enemies to biologically control
aphids. Potted chrysanthemums will be positioned in a 600 ft2 greenhouse
section following standard grower practices.
The experiment will utilize a factorial design with the following factors:
(a) aphid distributions clumped or randomly distributed within benches
(b) natural enemy release sites varying among 1 and 4 points, and
(c) at least two species of natural enemy will be studied.
Each experiment will be replicated 4 times. Approximately 10% of the
chrysanthemum plants within a replicate will be infested with 3 different
densities of aphids: 1, 10 and 100 per plant. One plant of each density
will be locate on each greenhouse bench, and infested plants will either
be clumped or randomly distributed within a bench. At the beginning of
the experiment, 3 natural enemies per plant will be released from either
1 central or 4 uniformity distributed locations within the greenhouse.
At two hour intervals after the natural enemy release (between 0700 and
1700 for a maximum of 3 consecutive days), each of the aphid infested plants
and an equal number of uninfested plants will be censused for natural enemies
(using a 2 minute observation time per pot).
Additionally, the behavior of the natural enemies (searching, attacking,
etc.) and their location within plants will be recorded. At the completion
of each trial the densities of live and parasitized aphids will be recorded
according to initial aphid density, pot location within the greenhouse
(relative to natural eneiriy release points), plant structure (leaf, terminal,
or stem), and the area of all plant structures (determined using a CIDTm
area meter). Two additional control treatments will also be monitored concurrently,
one to control for aphid population growth, the other to document natural
enemy survivorship. Temperature and humidity will be monitored continuously
using an Omnidata Model 220 datalogger. Variation in natural enemy impact
as a function of spatial distribution and number of release sites will
be assessed using analyis of variance (ANOVA) 17. The influences of natural
enemy dispersal and foraging behavior, aphid density per pot, and plant
architecture on levels of predation and parasitism patterns will be detected
using multiple regression analysis 3.
Objective 2. Measurements of natural enemy behavior within plants
is needed to determine the activities and efficacy of natural enemies once
they have located an infested plant. Combining the results from this objective
with the results from the Objective 1, and with our knowledge of aphid
distributions and aphid population dynamics (obtained during CY 1995),
I will be able to identify release rates and distributions necessary to
achieve biological control. These results will facilitate large-scale trials
to be conducted with cooperating growers (Objective 4). A 5 x 5 array of
chrysanthemum plants will be configured on a greenhouse bench with an aphid-infested
plant (with 1, 10 & 100 aphids per pot) in the center. Natural enemies
will be released from outside of the array and observed continuously. Upon
reaching the infested plant, the natural enemy behavior will be documented
with the aid of a hand-held computer (Psion HC 110) and behavioral observation
software (Observer 2.0) until they leave the infested plant, or a maximum
of 90 minutes. Natural enemies will be recaptured at the end of each run
to determine egg loads (eggs within ovaries) and body sizes, two covariates
of the observed behaviors. Experiments will be replicated with 30 individuals
per species and aphid density. The duration and frequence of each of the
natural enemy behaviors will compared across aphid densities using ANOVA
Objective 3. With guidance from Nancy Recheigl and Carl Scharfenberg
(Yoder Bros. Inc.), up to 10 chrysanthemum cultivars will be screened for
susceptibility to aphid population growth using choice and no choice tests.
Three cultivars (spanning the range of susceptibilty), selected from the
initial screening, will be used in population level studies to evaluate
the influence of cultiver suceptibility on aphid biological control. A
potentially interesting interaction is based upon preliminary data. While
susceptible cultivars allow aphid subpopulations to rapidly achieve densities
whereby biological control is impractical, if natural enemies demonstrate
a preference for aphid- dense plants, the presence of these susceptible
cultivars within a commercial chrysanthemum range may reduce the ability
of natural enemies to successfully control aphids on less susceptible varieties.
The above hypothesis will be tested by generating spatially variable mosaics
or blocks of the three aforementioned chrysanthemum cultivars. Each cultivar
will initially be innoculated with identical starting densities of aphids.
A week after the innoculation period, and when cultivar- specific variation
in aphid densities has been generated, natural enemies will be released
from one edge of the mosaic. Using the techniques outlined in Objective
1, natural enemy movement, aggregation, and efficacy will be measured for
each of the 6 possible cultivar mosaics, and each mosaic will be replicated
3 times. Among treatment (a treatment being one of the 6 mosaics) variation
in natural enemy movement, aggregation and efficacy will be detected using
ANOVA
Objective 4. To test the effect of natural enemy release patterns
on the outcome of augmentative biological control, three release patterns
based on (1) the average distance dispersed per day for C carnea and A.
colemani, (2) +1 standard deviation from the mean, and (3) -1 standard
deviation from the mean. Utilizing these three patterns, natural enemies
will be released into experimental chrysanthemum ranges of approximately
500 pots each to be provided by cooperating growers (Ellison’s Greenhouses,
Brenham, TX & Lone Star Growers, San Antonio, TX). Except for differences
in aphid management, the crop will be grown using standard practices. The
effectiveness of natural enemy releases will be determined by comparing
aphid populations within exclosures (which exclude natural enemies) with
aphid populations in experimental ranges receiving natural enemy release.
Each release distribution will be replicated 3 times for each of the 2
natural enemies for a total of 12 replicates. Prior to initiating natural
enemy releases, all of the plants within each treatment will be visually
inspected to insure similar aphid densities and spatial distributions across
replicates. Natural enemies will be release weekly into each of the chrysanthemum
ranges at a rate not to exceed 1 natural enemy per plant. Using a single
leaf and a single terminus as sample units, 10 leaves and 10 termini with
each exclosure cange and 30 leaves and 30 termini from each range outside
the cages will be sampled at random each week. Sampling will commence immediately
prior to the first release of natural enemies and will conclude with crop
harvest. Samples will be censused for the numbers of live and parasitized
aphids. Foliage with parasitized aphids will be held in individual petri
dishes and the emerging wasps will be identified to species. At harvest,
all leaves and termini from 40 plants selected at random from each range
will be inspected for the presence of aphids. For each plant, the percentage
of leaves infested with aphids and the numbers of aphids per leaf will
be determined. A repeated measures ANOVA 14 will be used to detect significant
among-treatment variations in live and parasitized aphid densities and
over sample dates.
Literature Cited
1 Cross, J. V. el al. 1983. IOBC/WPRS Bull. VI/3: 181-185.
2 Edwards, A.L. 1979. Multiple Regression and the Analysis of Variance
and Covariance. W.H. Freeman & Co.
3 Heinz, K.M. 1996. The Canadian Entomologist. In Press.
4 Heinz, K.M. & M.P. Parrella, 1990. Environ. Entomol. 19: 825-835.
5 Heinz, K.M. & M.P. Parrella. 1994a. Environ. Entomol. 23(5):
1346-1353.
6 Heinz, K.M. & M.P. Parrella. 1994b. Biological Control 4: 305-315.
7 Heinz, K.M., L. Nunney, & M.P. Parrella. 1993. Environ. Entomol.
22(6): 1217-1233.
8 Hunter, C.D. 1994. Suppliers of Beneficial Organisms in North America.
CDFA, CA.
9 Parrella, M.P., K.M. Heinz, & L. Nunney. 1992. American Entomologist
38(3): 172-179.
10 Rabasse, J.M. & I.J. Wyatt. 1985. In Biological Pest Control.
The Glasshouse Experience. Cornell University Press.
11 SAS Institute Inc. 1988. SAS/STAT User’s Guide, Release 6.03 Edition.
SAS Institute, Inc.
12 Scopes, N.E.A. 1969, Annals of Applied Biology 64: 433-439.
13 Scopes, N.E.A. & R. Pickford. 1985. In Biological Pest Control.
The Glasshouse Experience. Cornell University Press.
14 Sokal, R.R. & F.J. Rohlf. 1981. Biometry. W.H. Freeman and Co.
15 van Lenteren, J.C. 1986. In Insect Parasitoids. Academic Press.
16 van Steenis, M.J. 1993. IOBC/WPRS Bull. 16(2): 157-160.
17 Vehrs, S. & M.P. Parrella. 1991. California Agriculture 45:
28-29.
18 Wyatt, I.J. 1966. In Proceedings of the 3rd British Insecticide
& Fungicide Conference 1965.
Budget
Graduate research assistantship (100% time) 20,000
1 full-time research assistant (Mr. Brent Merrigan at 50% time) 10,000
Supplies and Equipment: Pots, soils, shipping of plant material, and
other miscellaneous items. 3,000
Travel: Travel from College Station to research plots provided by Cooperating
growers in Central (Elison’s Greenhouses) and South (Lone Star Growers)
Texas. 2,000
Total Request +: $ 35,000
* Funding is requested for a graduate student and a technician, both
will be dedicated solely to the research outlined in this proposal. The
graduate student will be enrolled an entomology- horticulture curriculum
at Texas A&M University. Mr. Brent Merrigan has been working with me
since March 29, 1995 and he will be retained as the technician in charge
of the project. He is well-trained and possesses the necessary talents
to perform the work outlined in this proposal. t The Texas Agricultural
Experiment Station will contribute 10% of Dr. Heinz’s salary and benefits
in the amount of $5,967 toward this project. + Texas A&M University
will contribute the indirect costs associated with administering this project
at the rate of 45% of the total costs, or $15,750.
Leader Qualifications
I have been an Assistant Professor in the Entomology Department of
Texas A&M University since September 1, 1994. The focus of my research
program is to develop biological control programs for annual cropping systems.
I maintain 1200 ft2 of greenhouse space and 2000 ft2 of laboratory space
with isolated insect rearing facilities to facilitate my research on the
use of predators and parasitoids to control arthropod pests of greenhouse
crops. My laboratory is well equipped to handle all of the above studies,
including 4 controlled environmental cabinets, 3 microscopes, 4 temperature
recording devices from Omnidata International Inc., a CIDO leaf area meter,
3 personal computers and printers, and complete video and photographic
systems for documenting natural enemy and aphid behavior. In addition,
I maintain ties with the Department of Horticulture, Texas A&M University
(Dr. Don Wilkerson) and with our floriculture extension faculty (Dr. Bart
Drees). All of the individuals for whom I am seeking support from the Endowment
are committed to the betterment of the floriculture and greenhouse industry.
In addition to the immediate impact this research will have on the industry,
the majority of funds will be used for the education and training of students
interested in pursuing careers in floriculture.
The combination of expertise, facilities, philosophy, and aid from the
Endowment guarantees that the proposed research will contribute to the
development of effective and environmentally safe biological control programs
for the floriculture industry. Three Recent Research Publications: (27
Total) Heizn, K.M., L.M. Heinz, & M.P. Parrella. 1996. Natural enemies
of western flower thrips indigenous to California ornamentals. Bulletin
of the IOBC (Greenhouse Working Group). In Press. Heinz, K.M. & J.M.
Nelson. 1996. Interspecific interactions among natural energies of Bemisia
in an inundative biological control program. Biological Control. In Press.
Heinz, K.M. 1996. Predators and parasitoids as biological control agents
of Bemisia in greenhouses. In (D. Gerling & R. T. Mayer, eds.) Bemisia
1995: taxonomy, biology, damage and management In Press. Three Recent Grower-Oriented
Publications: (37 Total) Heinz, K.M. 1996. Putting control in contact with
your aphids. Greenhouse Grower. Submitted. Heinz, K.M. & M. Rose. 1995.
Biological control in greenhouse crops: New regulations are being developed
that will equate beneficials with plant pests. GrowerTalks To be published
in August, 1995 issue. Heinz, K.M. & M.P. Parrella. 1994. Bios are
in Control. Greenhouse Grower. 12(12): 32 - 39. Studentes Supervised: 2
Ph.D. students, 1 M.A. student, 4 undergraduate projects Papers Presented:
(79 Total) 49 invited symposia, university lectures, and industry or scientific
conferences 30 submitted papers for scientific meetings.
