2011 Annual Report
1a.Objectives (from AD-416)
1 - Determine the behavioral, physiological, and genetic basis for host specificity of parasitoids of pest insects, such as soybean aphid (Aphis glycines) on soybean, Russian wheat aphid (Diuraphis noxia) on small grains, cherry vinegar fly (Drosophila suzukii) on soft fruits, and other invasive insects, and of insect herbivores, such as noctuid moths in the genus Heliothis on cotton and other crops.
1.1 – Determine the genetic architecture underlying differences in host
1.2 – Test whether parasitoids introduced against insect pests have evolved
to parasitize endemic species and whether parasitoids resident prior
to introductions have evolved to parasitize exotic pests.
1.3 – Test how the host acceptance behavior of parasitoids depends on their
physiological state, aphid defenses, and ecological factors.
1.4 - Determine the role of bacterial endosymbionts in protecting insects
2 - Determine the identity and phylogenetic relationships among species of parasitoids proposed for introduction against pest insects, such as soybean aphid, Russian wheat aphid, and cherry vinegar fly.
3 - Screen, introduce, and evaluate impact of candidates for biological control introductions against pest insects, such as the soybean aphid on soybean, the Russian wheat aphid on small grains, cherry vinegar fly on soft fruits, and other invasive insects.
3.1 – Biological control introductions against soybean aphid.
3.2 – Biological control introductions against Russian wheat aphid.
3.3 – Biological control introductions against cherry vinegar fly.
1b.Approach (from AD-416)
Safe and effective biological control depends on using narrowly host-specific agents, and host specificity depends on internal physiological state and previous experience, as well as ecological factors. Furthermore, the likelihood that a host-specific insect will evolve to attack a novel host species depends on the genetic architecture of host use. We will determine the behavioral and genetic bases for host shifts in the herbivores in the genus HELIOTHIS and aphid parasitoids in the genus APHELINUS using laboratory experiments on host use behavior and quantitative genetics/genomics analyses of inter and intraspecific crosses to map and identify genetic architecture. We will also test whether introduced aphid parasitoids have evolved to parasitize endemic species and whether aphid parasitoids resident prior to introductions have evolved to parasitize invasive pests. To do this, we compare host ranges parasitoids before and after introduction in laboratory experiments. Cryptic species are closely related species that differ little in the morphology, but differ critically in traits like host specificity, and studies on host range have often confounded cryptic species. Using modern methods of molecular phylogenetics, morphometrics, and behavioral biology, we develop robust phylogenies and identification keys for species complexes of aphid parasitoids important in biocontrol. We will use the knowledge and methods from the above research to screen specificity of candidates proposed for biocontrol introductions against soybean aphid, Russian wheat aphid, and other invasive pests. We will introduce the most promising candidates and evaluate their impact on target and non-target species with field exclosures, surveys, and analyses of population dynamics.
We continued mapping the genes affecting host specificity in APHELINUS species and HELIOTHIS species. For this, we developed a new protocol for making reduced representation libraries of genomic DNA that allow genotyping by sequencing with next-generation sequencing technology. We have sequenced six libraries with this protocol and are analyzing these libraries for sequence variation to use in mapping the genes involved in host specificity and in determining the relationships among parasitoid species. For mechanisms of host specificity, we determined in laboratory experiments that APHELINUS near GOSSYPII, a soybean aphid parasitoid new to science, showed a strong response to selection for parasitism of non-target species. This research relates to objective 1.1 of the project.
We conducted an experiment on the effect of a symbiotic bacteria of aphids (HAMITONELA DEFENSA) on resistance to parasitism by APHELINUS near ENGAEUS, a candidate for introduction against soybean aphid. This research relates to objective 1.4 of the project.
We continued with revision the systematics of the genus APHELINUS in cooperation with Texas A&M University. This research relates to objective 2 of the project.
For biological control of soybean aphid and Russian wheat aphid, we continued to collect and establish cultures of parasitoids in quarantine and test their host specificity. The host specifity testing revealed another APHELINUS species from Asia with a narrow host range that is a promising candidate for introduction to control soybean aphid. We obtained renewed funding from the North Central Soybean Research Program to support the work on soybean aphid biocontrol. We submitted a petition to the North American Plant Protection Organization for introduction of APHELINUS near ENGAEUS to control soybean aphid and the petition was approved; we plan to release this parasitoid in Minnesota in 2012. We determined that the quarantine colony of APHELINUS near ENGAEUS is still capable of winter diapause, which means that it should be able to overwinter in the northern mid-western soybean growing regions where it will be introduced. This research relates to objective 3.1 and 3.2 of the project.
Demonstrated change in host specificity of biological control agent. Evolutionary shifts in host specificity of insects introduced for biological control of foreign pests could affect non-target native species. The likelihood of such evolution is considered low, but few experiments have been done on the response to selection for changes in host specificity. In a laboratory experiment, ARS researchers at Newark, DE, found that APHELINUS near GOSSYPII, a parasitoid wasp that is a candidate for introduction for control of soybean aphid, showed a rapid response to selection for parasitizing a seldom attacked aphid species. This indicates that evolution of biological control agent specificity may be rapid in some circumstances, which reinforces the need to understand the genetics of host specificity. These results will benefit US agriculture by improving the safety of biological control introductions.
Approved petition for introduction of soybean parasitoid. Soybean aphid has become a major pest in the US causing damage to as much as 70 million acres of soybean crop per year. Biological control, using Asian parasitoids specific to soybean aphid, is a promising approach to control of this invasive soybean pest. After testing the specificity of 21 populations of Asian parasitoids during 10 years, ARS researchers at Newark, DE, identified the parasitic wasp APHELINUS near ENGAEUS as effective and safe for introduction. The North American Plant Protection Organization has approved a petition for introduction of this parasitoid into the midwestern US. Introduction of this biological control parasitoid could greatly reduce damage by soybean aphid to US soybean production.
Chaston, J.M., Dillman, A.R., Shapiro Ilan, D.I., Bilgrami, A., Gaugler, R., Hopper, K.R., Adams, B.J. 2011. Outcrossing and crossbreeding recovers deteriorated traits in laboratory cultured Steinernema carpocapsae nematodes. International Journal for Parasitology. 41:801-809.