Curtis Young (OSU Extension, Van Wert County) showed participants in this week’s BYGL Zoom Inservice pictures of the parasitoid wasp Itoplectis conquisitor (family Ichneumonidae). The wasps were all males, and they were milling around on this season’s bagworms (Thyridopteryx ephemeraeformis, family Psychidae) in northwest Ohio.
It is common for male insects to emerge before the females. The reproductive strategy means newly emerged females are quickly mated, lessening the time that they are exposed to life-threatening conditions such as being attacked by predators. Indeed, according to the scientific literature, I. conquisitor females emerge about four days behind the males.
The images below show an I. conquisitor female that I extracted a few years ago from a dead bagworm. Note the prominent ovipositor.
The images below show the male wasps, denoted by the lack of ovipositors. The gathering of the males did not appear to be random behavior. We speculated that the nascent females were emitting chemical or physical signals to draw in the males.
The scientific literature reports that I. conquisitor targets pre-pupae and pupae and is a highly polyphagous lepidopteran specialist known to parasitize over 100 species of moths and butterflies. It may also behave as a hyperparasitoid by developing in the cocoons of other parasitoids, including other ichneumonids as well as braconids.
However, I. conquisitor appears to have a particular “taste” for bagworms. Although the literature notes that bagworms are targeted by several wasp parasitoids, I. conquisitor dominates with parasitism rates ranging from 58% to 75.9%.
Bagworms have one generation per season (univoltine) with eggs hatching in late May to early June. Thus, the pre-pupal and pupal stages targeted by the wasp don’t appear until late summer. However, I. conquisitor has multiple generations (multivoltine). The literature notes that earlier generations develop in other lepidoptera before appearing on the scene to attack bagworms.
Bagworm Management by Connecting the Dots
This bagworm management strategy has been included in several of the past BYGL Alerts about bagworms because it connects landscape diversity with a reduction in plant pests, particularly by providing a diverse selection of flowering plants. So, how does the abundance of flowering plants translate into fewer plant pests?
It’s well documented that a wide range of enemies of insect pests are fueled by nectar. In other words, an effective long-term bagworm pest management strategy is to simply plant flowering plants that provide nectar.
Bagworms are commonly targeted by an array of predators, parasitoids, and pathogens (the 3-Ps). It’s common to find bagworm bags ripped open by predaceous wasps, such as baldfaced hornets (Dolichovespula maculata), to extract the caterpillar meat morsels inside. Of course, these wasps are commonly observed visiting flowers for a nectar-charge, meaning they are also pollinators.
As noted above, I. conquisitor is one of the most common parasitoid that attacks bagworms. The literature notes that the female wasps behave like many other hymenopteran parasitoids by using their ovipositors to skewer lepidopteran caterpillars and pupae to release protein-rich fluids that the wasps consume to support egg development. This feeding behavior alone can kill bagworm caterpillars.
Both male and female I. conquisitor wasps visit flowers to acquire carbohydrate-rich nectar for energy, which the females use to search for bagworm victims. Thus, the wasps are both pollinators and enemies of bagworms.
A 2005 study showed parasitism rates of I. conquisitor exceeded 70% in bagworm-infested plants next to a central flower bed but less than 40% in infested plants with flower beds further away. In other words, an effective insecticide-free long-term bagworm management strategy is to simply plant flowering plants that attract pollinators, including parasitoid wasps.
On a final note, we have long recommended removing and destroying bagworms beginning at this time of the year. This management tactic will eliminate developing bagworm males and females and eventually destroy eggs. However, this tactic may have unintended consequences in light of the potential help provided by I. conquisitor in reducing bagworm populations. Plucking bagworms now risks eliminating the wasps.
Removing and destroying bagworms should be delayed for perhaps another month. This allows enough time for the wasps to emerge and mate, so there will be plenty of mated females available next season to continue providing natural suppression of lepidopteran caterpillars, including bagworms.
Selected References:
Beukeboom, L. W., Kamping, A., Louter, M., Pijnacker, L. P., Katju, V., Ferree, P. M., & Werren, J. H. (2007). Haploid females in the parasitic wasp Nasonia vitripennis. Science, 315(5809), 206-206.
https://www.science.org/doi/10.1126/science.1133388
Cronin, J. T., & Gill, D. E. (1989). The influence of host distribution, sex, and size on the level of parasitism by Itoplectis conquisitor. Ecological Entomology, 14, 163-173.
https://doi.org/10.1093/ee/37.5.1307
Ellis, J. A., Walter, A. D., Tooker, J. F., Ginzel, M. D., Reagel, P. F., Lacey, E. S., ... & Hanks, L. M. (2005). Conservation biological control in urban landscapes: manipulating parasitoids of bagworm (Lepidoptera: Psychidae) with flowering forbs. Biological Control, 34(1), 99-107. https://doi.org/10.1016/j.biocontrol.2005.03.020
Leius, K. (1961). Influence of food on fecundity and longevity of adults of Itoplectis conquisitor (Say) (Hymenoptera: Ichneumonidae). The Canadian Entomologist, 93(9), 771-780.
https://doi.org/10.4039/Ent93771-9
Moser, S. E., Alleyne, M., Wiedenmann, R. N., & Hanks, L. M. (2008). Influence of oviposition experience on multiparasitism by Pimpla disparis Vierick and Itoplectis conquisitor Say (Hymenoptera: Ichneumonidae). Environmental entomology, 37(5), 1307-1312.
https://doi.org/10.1093/ee/37.5.1307
Raupp, M. J., Shrewsbury, P. M., & Herms, D. A. (2010). Ecology of herbivorous arthropods in urban landscapes. Annual review of entomology, 55(1), 19-38.
https://doi.org/10.1146/annurev-ento-112408-085351
Raupp, M. J., Shrewsbury, P. M., & Herms, D. A. (2012). Disasters by design: outbreaks along urban gradients. Insect outbreaks revisited, 311-340.
https://doi.org/10.1002/9781118295205.ch15
Riley, C. B., Raupp, M. J., Fite, K. L., & Gardiner, M. M. (2022). Woody plant biodiversity explains arthropod pest management interventions in residential landscapes. Urban Forestry & Urban Greening, 67, 127439.
https://doi.org/10.1016/j.ufug.2021.127439
Sheppard, R. F., & Stairs, G. R. (1976). FACTORS AFFECTING THE SURVIVAL OF LARVAL AND PUPAL STAGES OF THE BAGWORM, THYRIDOPTERYX EPHEMERAEFORMIS (LEPIDOPTERA: PSYCHIDAE) 1. The Canadian Entomologist, 108(5), 469-473. https://doi.org/10.4039/Ent108469-5
Townes, H., & Townes, M. (1960). Ichneumon-Flies of America North of Mexico: 2. Subfamilies Ephialtinae, Xoridinae, Acaenitinae. United State National Museum Bulletin 216: 1-676.
http://hdl.handle.net/10088/10225
Townes Jr, H. K. (1940). A revision of the Pimplini of eastern North America (Hymenoptera, Ichneumonidae). Annals of the Entomological Society of America, 33(2), 283-323.
https://doi.org/10.1093/aesa/33.2.283
