Source: UNIV OF MASSACHUSETTS submitted to NRP
IMPROVED METHODS FOR ESTIMATING PARASITOID HOST RANGES IN THE LABORATORY, IN SUPPORT OF BIOLOGICAL CONTROL INTRODUCTIONS
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
COMPLETE
Funding Source
NRI COMPETITIVE GRANT
Reporting Frequency
Annual
Accession No.
0192599
Grant No.
2002-35316-12196
Cumulative Award Amt.
(N/A)
Proposal No.
2002-01981
Multistate No.
(N/A)
Project Start Date
Sep 1, 2002
Project End Date
Aug 31, 2005
Grant Year
2002
Program Code
[51.7]- (N/A)
Recipient Organization
UNIV OF MASSACHUSETTS
(N/A)
AMHERST,MA 01003
Performing Department
PLANT, SOIL & INSECT SCIENCE
Non Technical Summary
Parasitoids released for biological control projects may attack nontarget native insects. This project will determine how testing conditions may affect host preferences observed in tests. This can be used to design tests that more accurately predict field host ranges
Animal Health Component
50%
Research Effort Categories
Basic
50%
Applied
50%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
21131101130100%
Knowledge Area
211 - Insects, Mites, and Other Arthropods Affecting Plants;

Subject Of Investigation
3110 - Insects;

Field Of Science
1130 - Entomology and acarology;
Goals / Objectives
Our objectives all relate to developing a better understanding of which factors, among those potentially affecting the host acceptance behavior of Cotesia rubecula vs. C. glomerata (two parasitoids used as biological control agents), actually influence outcomes of host range tests. In particular we are interested in understanding which of these might cause laboratory estimates to fail to accurately predict realized field host ranges. This is a model system. Our interest is in understanding factors affecting host range as measured by such tests, so they may be used as accurately as possible in suporting petitions for natural enemy introductions and best protect native species from unintended attack. Our specific objects are a series of factors that potentially affect host preference expressed in such tests. These are list below. Only 1-6 will be addressed with the reduced funding awarded. Other sources of funding will be sought to address the numbers 7 and 8. Obj. 1. Light Scattering Effect. Determine effect of white (light scattering) vs. black (non-scattering) test cage fabric. Obj.2. Test Arena Size Effect. Determine effect of running tests in various sized arenas. Obj.3. Egg Load and Hunger Effects. Determine effect of egg load (high vs. low) and hunger level (honey fed vs. starved) on parasitoids' host preferences. Obj.4. Learning-the-Host Effect. Determine effect of prior multiple ovipositions in a given host on subsequent host preferences. Obj.5. Plant Effect. Determine the effect of the insect-host plant complex for P. napi vs. P. rapae on each of two host plants (Brassica oleracea vs. Cardamine diphylla). Obj.6. Herbivore-Induced Plant Volatiles Effect. Determine the effect of volatiles emitted by plants (B. oleracea only) fed on by P. napi vs. P. rapae, but in the absence of host feces. Obj.7. Feces Volatiles Effect. Determine the effect of feces volatiles (P. napi vs. P. rapae, both on B. oleracea) on parasitoid landing rates on plants with larvae, but not host feeding. Obj.8. Contact Kairomones Effect. Determine if after landing, contact with kairomones determines host preference between larvae of P. napi vs. P. rapae by either parasitoid.
Project Methods
We will use laboratory colonies of both Cotesia and Pieris species (as larvae) to see which of the six factors below affects results of host range tests. Obj. 1. Light Scattering Effect. We will use small cages (38h X 61 X 38 cm) with either white organdy (that scatters light) or a sheer black organdy that does not scatter light, placing larvae of both butterflies in each cage, in a greenhouse under natural light. The test will also be run outdoors. Obj.2. Test Arena Size Effect. Using standard parasitoids and B. oleracea plants, we will examine the effect of cage size on parasitism of both Pieris species by each parasitoid, in (1) small cages (plastic cubes, 30 cm on a side), (2) large cages (153 cm L x 92 W x 117 H), and (3) open greenhouses ( 8 x 4 m). Obj.3. Egg Load and Hunger Effects. There will be four treatments: (1) low hunger, moderate egg load, (2) low hunger, high egg load, (3) high hunger, moderate egg load, and (4) high hunger, high egg load. The first two can be achieved by feeding honey ad lib and holding parasitoids without hosts for various periods before tests. Treatments 3 and 4 would be achieved by holding wasps with either no honey for a short and long time, allowing eggs to develop. Obj.4. Learning-the-Host Effect. There will be six treatment groups: (1) C. glomerata preconditioned to P. rapae, (2) C. glomerata preconditioned to P. napi, (3) C. rubecula preconditioned to P. rapae, (4) C. rubecula preconditioned to P. napi, (5) unconditioned C. glomerata, and (6) unconditioned C. rubecula. Preconditioning will consist of exposure of a female for one hour to a small collard plant on which there are 10 second instars of the host to which the parasitoid is being conditioned. Once larvae are prepared they will be exposed to parasitoids and parasitism measured. Obj.5. Plant Effect. Using Brassica oleracea, Cardamine diphylla, Sisymbrium officinale, Barbarea vulgaris, and Brassica rapa, we will expose laboratory-reared second instars of both species, in large cages, and measure attack rates by each parasitoid. Obj.6. Herbivore-Induced Plant Volatiles Effect. we will use the big cage. There will be four treatments: caterpillars without feeding and caterpillars with fresh feeding, crossed by each species of caterpillar. We will achieve the second treatment simply by placing caterpillars on plants and letting them feed for 4 fours before the start of the test. . To create the caterpillars without feeding treatment, we will use superglue to glue shut the mandibles of the test caterpillars and then place them on the test plants at the start of the test. Treatments will be exposed to parasitoids under standard conditions and rate of parasitism measured.

Progress 09/01/02 to 08/31/05

Outputs
Overview of results. Only objs. 1 and 2 were addressed because we experienced extreme difficulties with rearing colonies. Also an unexpected finding in the field cast the original premise of the proposal in doubt. Rearing of large numbers of the two butterflies was marginal. Rearing of P. rapae in artificial diet was developed as a solution to a pathogen in the colony, but reared larvae remained prone to infections. Rearing of P. napi in artificial diet was developed but productivity of the colony declined over time and rearing on plants was resumed. Rearing of Cotesia rubecula and C. glomerata required hand stinging, as mass stinging in cages was not consistently productive. Hand stinging was labor intensive and restricted numbers of wasps that could be obtained. A problem with a male biased wasp sex ratio due to poor mating arose but was resolved by changing the physical conditions under which wasps were held, moving wasps into larger cages with fans to provide small amounts of air movement. The above mentioned difficulties with rearing caused the PhD student working on the project to quit after two years and take a non-thesis masters. Restarting the project with a new student was not financially feasible. Work was continued with a technician. Field tests (not part of the original proposal) were undertaken to reconfirm the basic premise of the proposal: that C. rubecula does not sting P. napi larvae in the field. P. rapae and P. napi larvae were exposed at two locations where C. rubecula was known to occur. Exposures were made in May-July of 2005 on 14 site X date combinations. Of 245 P. rapae recovered for dissection (after two day exposures), 21% (52) were parasitisized by C. rubecula. But 3% (9) of the 291 P. napi larvae exposed were also attacked. This was the first field observation of parasitism of this host by this parasitoid in New England. This called into question the basic premise of the grant (that lab factors were leading to false positives that did not occur in the field). A second field experiment was run to see if distance between larvae of P. rapae and those of P. napi might explain attack on P. napi (we predicted only P. napi close to P. rapae might be attacked). But for exposures of larvae where the distance between potted plants with the two species was varied from 0 m (pot to pot), 1 m or 3 m, no effect of distance was detected. Other results are as indicated: Obj. 1. Light Scattering Effect. Parasitism rates were not affected by color of fabric of test cages (black, non light scattering vs white, light scattering) Obj.2. Test Arena Size Effect. Parasitism decreased with increase in the arena size (a trivial effect), but selectivity (ratio of attacks on P. napi relative to P. rapae) was not affected by arena cage size, providing no explanation for the originally observed discrepancy between lab and field results. Obj.3. Egg Load and Hunger Effects. Not done (see above). Obj.4. Learning-the-Host Effect. Not done (see above Obj.5. Plant Effect. Not done (see above). Obj.6. Herbivore-Induced Plant Volatiles Effect. Not done (see above). Analysis of all results and publication is pending.

Impacts
This project has highlighted the difficulty in multispecies projects with high rearing needs. It has advanced marginally our understanding of host specificity of the Cotesia species investigated and methods for making such determinations.

Publications

  • No publications reported this period


Progress 10/01/03 to 09/30/04

Outputs
Rearing problems slowed progess on this project. Of the four species required for the project, Pieris rapae is now being reared efficiently on an artificial diet, allowing us to more effectively protect the culture from pathogens. Using this as the rearing host, both parasitoids (Cotesia glomerata and Cotesia rubecula) are being reared on hosts feeding on artificial diet. Problems arose this year with the colony of Pieris napi, which previously was reared without difficulty on whole plants. A pathogen invaded the colony in summer of 2004, preventing much of the planned summer work and requiring us to develop an artificial diet suitable for rearing this butterfly. Currently, a viable colony of this species (still on whole plants) has been reestablished and modificiation of the P. rapae diet (by adding a mustard oil compound as a feeding stimulant) is being investigated. Objective 1 (effect of light scattering) was addressed this year. No effect of light scattering (light vs dark fabric in test cages) was found on the host preferences of either parasitoid. Work is underway on Objective 2 (size of test arena).

Impacts
The long term expected impact of this project will be to improve our understanding of laboratory test arena factors that may bias estimates of parasitoid host ranges. Such improved understanding will lead to more accurate host range forecasts in classical biological control projects involving parasitoids, making them safer to native insects.

Publications

  • No publications reported this period


Progress 10/01/02 to 09/30/03

Outputs
A PhD graduate student from New Zealand was recruited, arriving January of 2003. This student spent the summer of 2003 collecting colonies of the four species required for the project (two butterflies: Pieris rapae and Pieris napi, and two parasitoids Cotesia rubecula and C. glomerata). All insects are now in colony. A problem arose in that a pathogen occurred in the Pieris rapae colony. Initial efforts to establish a pathogen free colony via rearing of separate families failed. In response, the rearing procedure was converted to one based on the use of an artificial diet. This is now working well. Experiments for the project are expected to start in winter of 2003-2004.

Impacts
The long term expected impact of this project will be to improve our understanding of laboratory test arena factors that may bias estimates of parasitoid host ranges. Such improved understanding will lead to more accurate host range forecasts in classical biological control projects involving parasitoids, making them safer to native insects.

Publications

  • No publications reported this period


Progress 10/01/01 to 09/30/02

Outputs
This is a new project funded in the summer of 2002. I have made progress by sucessfully recruiting a graduate student (Tara Murray) from New Zealand from the lab of Barbara Barratt, a world authority on topics similar to those addressed in the grant proposal. Work is expected to start in January of 2003 following the arrival to MA of the student.

Impacts
The work has not started so, this section is being used to describe anticipated impact. Impact will occur at two levels. First, researchers in biological control will be affected because they will benefit from new information on how to design more predictive host range tests for parasitoids. Second, the public will benefit later because released parasitoids will have better known host ranges and thus be less likely to attack non-target species.

Publications

  • No publications reported this period