Shared field knowledge · free to use
Field allies: who eats Japanese beetles and hemp borers?
A plain-language summary for Wisconsin hemp and garden neighbors: which animals help with Japanese beetle adults and grubs, and why Eurasian hemp borer is different. Includes insect parasitoid helpers listed by climate zone. Offered as public education — not a product pitch.
We publish this so growers can plan scouting and habitat without myths. Take what helps; leave wildlife and tiny wasps as background helpers, not a guarantee.
Separate from labels & marketing hype
This page is field biology and stewardship education. It is not a pesticide product label (FIFRA), not consumer package labeling, and not a claim that wildlife or parasitoids eliminate pests. Marketing claims and pesticide labels stay on separate tracks.
Quick matrix
| Animal | JB adults | JB grubs | EHB (stem borer) |
|---|---|---|---|
| Raccoons / opossums | Low / occasional | Yes — dig soil | Very low |
| Birds (many species) | Yes | Yes — probe soil | Low on stem larvae; moths opportunistic |
| Insect parasitoids | Limited (some flies/wasps) | Tiphia-type on grubs (regional) | Primary helpers — eggs & larvae by climate |
| Deer | No | No | No |
Japanese beetle
Popillia japonica
Adults
Metallic green and copper beetles that skeletonize leaves of many plants, including hemp.
Grubs
White C-shaped larvae in soil, mostly feeding on grass and turf roots — next year’s beetles.
Who eats them?
Birds: Many birds eat adults and/or grubs: starlings, grackles, robins, crows, blue jays, sparrows, cardinals, turkeys, and domestic ducks or chickens in yards. Helpful, rarely enough alone under heavy flights.
Raccoons & opossums: Raccoons and opossums dig for grubs in soil and turf (often at night). They may sample adults occasionally. Digging can tear sod; do not bait them at pump houses or trash for “pest control.”
Deer: White-tailed deer are plant-eaters. They do not control Japanese beetles or hemp borers. They may browse hemp — a crop risk, not a pest solution.
Eurasian hemp borer
Grapholita delineana
A small moth whose larvae may chew leaves early, then bore into stems. Once inside, they are hard for birds or mammals to reach.
Vertebrates: Birds may take flying moths or exposed young larvae opportunistically. Raccoons, opossums, and deer are not meaningful stem-borer controls.
Insect allies: The real allies are often tiny: parasitic wasps and flies (parasitoids) that attack eggs or larvae. See climate-zone lists below.
For hemp borer, insect parasitoids matter far more than raccoons, opossums, birds, or deer.
Hemp borer insect parasitoids by climate zone
Once larvae are inside stems, vertebrates rarely help. These insect helpers attack eggs or larvae. Lists combine Grapholita / tortricid IPM guilds (planning proxy when local EHB surveys are thin) with regionally present generalists. Habitat for adult wasps and flies matters as much as the names.
Not a FIFRA product list, not commercial biocontrol sales, and not a guarantee of control. Specialist complexes are often richer in the Eurasian native range than in newly invaded North American fields. Species presence varies by year, bloom, and spray history.
Humid continental — Upper Midwest
WI, MN, MI, northern IL / IN / OH, IA, southern Ontario
Cold winters, warm summers; EHB pressure documented in Columbia County–class Wisconsin hemp systems.
Habitat for helpers: Flowering field edges (Apiaceae, Asteraceae), unsprayed hedgerows, reduced broad-spectrum pyrethroid use during moth flights.
- Trichogramma egg waspsTrichogramma spp. (e.g. T. minutum, T. pretiosum complexes)Attacks: eggsGrapholita / tortricid guild — planning proxy
Minute wasps that parasitize moth eggs before larvae enter stems. More reliable as a guild than a single species guarantee.
- Braconid larval waspsBraconidae (Macrocentrus-type and related genera in Grapholita systems)Attacks: larvaeGrapholita / tortricid guild — planning proxy
Larval parasitoids known from related Grapholita pests; local EHB confirmation needs rearing from stems.
- Ichneumonid waspsIchneumonidae (e.g. Glypta-type guilds on tortricids)Attacks: larvaeGrapholita / tortricid guild — planning proxy
Larger parasitic wasps in wooded and mixed farm landscapes; attack concealed tortricid larvae in other crops.
- Tachinid parasitoid fliesTachinidae (various)Attacks: larvae (sometimes late instars / prepupae)Regionally present generalist
Associations noted in hemp-borer / Grapholita systems; adults need nectar.
- Other chalcidoid waspsChalcidoidea (beyond Trichogramma)Attacks: eggs / early larvaeRegionally present generalist
Diverse small wasps in diverse plantings; rarely identified to species in grower scouting.
Humid subtropical — Mid-South & lower Midwest
KY, TN, NC, VA, southern IL / IN / MO, northern AR / MS / AL
Longer warm season; more generations possible; EHB reported on transplants and mother plants in states such as Kentucky.
Habitat for helpers: Long-season nectar strips, cover crops that flower between plantings, caution with repeated broad-spectrum sprays on mother stock.
- Trichogramma egg wasps (warm-season complexes)Trichogramma spp. (including T. pretiosum and related)Attacks: eggsGrapholita / tortricid guild — planning proxy
Warm-region egg parasitoid guild for moth pests; same early-window logic for EHB eggs.
- Trichogramma (corn borer / moth-egg guilds)Trichogramma ostriniae and related egg parasitoidsAttacks: eggsRegionally present generalist
Common in Mid-South corn and vegetable systems; may spill into hemp landscapes.
- Macrocentrus-type braconidsMacrocentrus spp. (Grapholita systems)Attacks: larvaeGrapholita / tortricid guild — planning proxy
Classic larval parasitoids of Grapholita in fruit/tortricid IPM literature — planning guild for EHB stem larvae.
- Ascogaster-type braconidsAscogaster spp.Attacks: eggs / early larvaeGrapholita / tortricid guild — planning proxy
Egg–larval braconids known from related Grapholita pests.
- Tachinid parasitoid fliesTachinidaeAttacks: larvaeRegionally present generalist
Diverse in humid landscapes with floral resources.
High Plains / semi-arid continental
CO, WY, MT, western KS / NE / ND / SD, eastern NM
Lower humidity, wind, irrigation-driven hemp; parasitoid communities often thinner without floral habitat.
Habitat for helpers: Irrigated flower strips and shelterbelts matter more; bare pivots support fewer adult wasps.
- Trichogramma egg waspsTrichogramma spp.Attacks: eggsRegionally present generalist
Present where moth eggs and microhabitat humidity allow; do not assume high parasitism without scouting.
- Braconid wasps (tortricid guild)BraconidaeAttacks: larvaeGrapholita / tortricid guild — planning proxy
Guild-level planning; species lists lean on irrigated fruit/vegetable Grapholita systems nearby.
- Ichneumonid waspsIchneumonidaeAttacks: larvaeRegionally present generalist
Often tied to woody edges and alternate tortricid hosts.
- Tachinid fliesTachinidaeAttacks: larvaeRegionally present generalist
Need nectar; drought and herbicide-clean edges reduce adults.
Marine west coast — Pacific Northwest
western WA, western OR, coastal BC
Mild wet winters, cool summers; tortricid parasitoid guilds known from fruit and forest edges.
Habitat for helpers: Hedgerows, berry and orchard edges, and continuous green cover favor chalcidoids and ichneumonids.
- Trichogramma egg waspsTrichogramma spp.Attacks: eggsRegionally present generalist
Egg parasitoid guild in regional moth systems.
- Braconid larval waspsBraconidaeAttacks: larvaeGrapholita / tortricid guild — planning proxy
Planning guild from Grapholita / orchard tortricid literature adapted to cool maritime climates.
- Ichneumonid waspsIchneumonidaeAttacks: larvaeRegionally present generalist
Often abundant along forest–farm margins.
- Tachinid fliesTachinidaeAttacks: larvaeRegionally present generalist
Floral resources in cool-season plantings support adults.
Eurasian native range (literature specialists)
Europe, temperate Asia (native / long-established G. delineana range)
Where EHB evolved with hemp, specialist and oligophagous parasitoid complexes are historically richer than in many North American fields.
Habitat for helpers: Traditional hemp–crop mosaics with unsprayed margins historically supported higher parasitism rates in published notes.
- Trichogramma egg waspsTrichogramma spp.Attacks: eggsNative-range / literature association
Egg parasitoids figure in Eurasian Grapholita / hemp-borer natural-enemy discussions.
- Braconid waspsBraconidae (multiple genera)Attacks: eggs / larvaeNative-range / literature association
Core larval and egg–larval guild in Old World hemp-belt tortricid systems.
- Ichneumonid waspsIchneumonidaeAttacks: larvaeNative-range / literature association
Reported in broader Grapholita natural-enemy complexes.
- Tachinid fliesTachinidaeAttacks: larvaeNative-range / literature association
Parasitoid fly associations noted in hemp-borer literature themes.
All U.S. hemp climates — conservation helpers
Any licensed hemp region
Not climate-specific: practices that keep parasitoid adults alive anywhere EHB is present.
Habitat for helpers: Nectar for adults, alternate moth hosts in edges, avoid calendar broad-spectrum sprays during flight and egg lay.
- Spiders (generalist predators, not parasitoids)AraneaeAttacks: exposed eggs / young larvae / mothsConservation practice (all zones)
Predators, not parasitoids — help exposed stages only.
- Ground beetles & ants (opportunistic)Carabidae; FormicidaeAttacks: exposed stages / fallen larvaeConservation practice (all zones)
Not stem-interior control; background mortality only.
- All adult parasitoid wasps & tachinids—Attacks: — (adult feeding)Conservation practice (all zones)
Adults need sugar (nectar, honeydew). Clean tillage + zero bloom starves helpers even when larvae are present.
What we do in the field
- Treat wildlife and parasitoids as background help — not a spray substitute and not a marketing guarantee.
- On small fiber or wild stands: hand-pick Japanese beetle adults into soapy water in the cool of day.
- Scout stems for hemp borer (entry holes, frass, wilt); surface sprays miss larvae already inside stems.
- Leave flowering edges so adult wasps and tachinids have nectar during moth flight and egg lay.
- Bird water and nesting habitat can support insectivores; deer fencing protects plants, not beetles.
- Any chemical control needs a product labeled for hemp (EPA use site) and registered in your state — separate from this page.
Keep learning
Educational synthesis of extension and pest-management literature. Predation and parasitism are incomplete. Deer and some birds can also damage crops. Confirm any spray on the current EPA label and Wisconsin registration. Not legal advice.