Taxonomic issues related to biological control prospects for the ragweed borer, Epiblema strenuana (Lepidoptera: Tortricidae)

The ragweed borer, Epiblema strenuana (Walker, 1863), has a long history of use as a biological control agent against important weed pests in the family Asteraceae. Recently, E. strenuana has been reported feeding on the invasive perennials Ambrosia confertiflora and A. tenuifolia in Israel. The geographic location of Israel has raised concern over the possibility that the moth may spread to areas such as Ethiopia where the oil-seed crop Guizotia abyssinica is cultivated, as this is a potential host for E. strenuana. However, the taxonomic status of E. strenuana and a current synonym, E. minutana (Kearfott, 1905) is unclear. These taxa have been treated as separate species in the past, and they potentially have different feeding habits and damage different parts of the plant. We analyzed DNA data and adult morphology and determined that E. minutana, stat. rev., is a valid species which we raise from synonymy with E. strenuana. Wing coloration, the shape of the female sterigma, and COI DNA barcodes are consistently different between the two species. We also determined that the species previously identified as E. strenuana in Israel is actually E. minutana. While detailed host range tests have been conducted on the E. strenuana populations released in Australia and China, the host range of E. minutana remains to be clarified. We discuss the history of biological control using E. strenuana and the implications for finding E. minutana in Israel. We also provide species redescriptions for E. strenuana and E. minutana and illustrate diagnostic characters.

Nontarget Host Risk Assessment of the Egg Parasitoid Trichogrammatoidea cryptophlebiae (Hymenoptera: Trichogrammatidae) for Classical Biological Control of the False Codling Moth (Lepidoptera: Tortricidae) in Israel

The false codling moth Thaumatotibia leucotreta (Meyrick), is an invasive species in Israel. In order to carry out a classical biological control program, the African egg parasitoid Trichogrammatoidea cryptophlebiae (Nagaraja) was recently introduced into Israel, and nontarget host risk assessment was performed as required. In no-choice tests we determined that T. cryptophlebiae was unable to develop in eggs of four nontarget Lepidopteran species: Pectinophora gossypiella (Saunders), Spodoptora littoralis (Boisduval), Ephestia kuehniella (Zeller), and Belenois aurota (Fabricius). Conversely, it developed in three Lepidopteran species eggs of the Tortricidae family: Cydia pomonella (Linnaeus), Lobesia botrana (Denis and Schiffermüller), and Epiblema strenuana (Walker). Epiblema strenuana eggs showed the lowest parasitism level among all tested moth eggs of the Tortricidae family. The progeny production of parasitized false codling moth eggs was similar to that of C. pomonella eggs, but smaller than that of L. botrana eggs. However, moth egg and parasitoid clutch sizes were smallest on L. botrana eggs and largest on C. pomonella eggs. In choice bioassays, T. cryptophlebiae significantly preferred to parasitize T. leucotreta eggs over the eggs of C. pomonella, L. botrana, and E. strenuana. Moreover, the choice of T. leucotreta eggs over the eggs of L. botrana was not affected by the parasitoids’ rearing histories. Our data support the assumption that T. cryptophlebiae develops only in moth species of the Tortricidae family. Thus, the risk that it may attack nontarget species is low.

Biological Control of Parthenium (Parthenium hysterophorus) in Australian Rangeland Translates to Improved Grass Production

Biological control of parthenium, a major weed in grazing areas in Australia, was initiated in the mid 1970s. Since then, nine species of insects and two rust fungi have been introduced. Evaluation using pesticide exclusion at two sites (Mt. Panorama and Plain Creek) in Queensland, Australia, revealed that classical biological control had a significant negative effect on the target weed, but the impact varied between years. In this study, I quantified the effects of biological control of parthenium on grass production. Grass production declined with the increase in parthenium biomass. Significant increase in grass production due to biological control was observed, but only in 1 of 4 yr at Mt. Panorama and 2 of 4 yr at Plain Creek. At Mt. Panorama, there was a 40% increase in grass biomass in 1997 because of defoliation by Zygogramma bicolorata and galling by Epiblema strenuana. At Plain Creek, grass biomass increased by 52% in 1998 because of E. strenuana and by 45% in 2000 because of combined effects of E. strenuana and the summer rust Puccinia melampodii. This study provides evidence on the beneficial effects of biological control of parthenium in areas under limited grazing.

Seasonal variation in the effectiveness of the leaf-feeding beetle Zygogramma bicolorata (Coleoptera: Chrysomelidae) and stem-galling moth Epiblema strenuana (Lepidoptera: Tortricidae) as biocontrol agents on the weed Parthenium hysterophorus (Asteraceae)

Variation in the effectiveness of biocontrol agents on the weed Parthenium hysterophorus L. was evaluated at two properties (Mount Panorama and Plain Creek) in Queensland, Australia for four years (1996–2000) using a pesticide exclusion experiment. At Mount Panorama, higher levels of defoliation by the leaf-feeding beetle Zygogramma bicolorata Pallister and galling by the moth Epiblema strenuana Walker in 1996–97 coincided with an above average summer rainfall, but in the following three years with below average summer rainfall the defoliation and galling levels were significantly lower. Biocontrol had significant negative impact on the weed only in 1996–97 with no major impact in the following three years. At Plain Creek, galling by E. strenuana was evident in all the four years, but varied significantly between years due to non-synchrony between P. hysterophorus germination and E. strenuana emergence. At Plain Creek biocontrol had limited impact on the weed in 1996–97 and 1997–98, with no significant impact in the following two years. Over the 4-year period, defoliation and galling resulted in 70% reduction in the soil seed bank at Mount Panorama, but the reduction in the soil seed bank at Plain Creek due to galling was not significant. Effectiveness of Z. bicolorata and E. strenuana was dependent on weather conditions and as a result had only limited impact on the weed in three out of four years.