Entomopathogenic Nematode
Heterorhabditis indica
📖 Description
Heterorhabditis indica is the most commercially important entomopathogenic nematode (EPN) species in Indian agriculture and a native of Indian soils first described from Tamil Nadu in 1992. It is a steinernematid-Heterorhabditid complex: the infective juvenile (IJ) carries the symbiotic bacterium Photorhabdus luminescens in its gut, seeks out insect hosts in soil using CO2 and other kairomones, enters the host through natural openings (mouth, anus, spiracles), and releases the bacterium into the host’s haemocoel. The bacterium multiplies rapidly, kills the host within 24–48 hours by septicaemia, and digests host tissues into a nutrient-rich broth that the nematodes feed on. The nematode completes 2–3 generations inside the host cadaver before emerging as new infective juveniles to seek new hosts. H. indica is mass-reared by several Indian biocontrol laboratories (NBAIR Bengaluru, IIHR Bengaluru, UAS Dharwad) and applied against white grubs, root weevils, and fruit fly pupae in sugarcane, groundnut, vegetables, cardamom, tea, coffee, mango, and cucurbits. Estimated value of biological control services provided by H. indica and related EPN species in Indian agriculture exceeds ₹500 crore per year — primarily through avoided insecticide costs and reduced white-grub-related yield losses in sugarcane and groundnut.
⚠️ Symptoms to watch for
- No plant damage — this is a beneficial biocontrol agent. Visible mortality of soil-dwelling insect larvae within 48–72 hours of application, characteristic orange-red colour and soft, flaccid texture of infected larvae, larval cadavers found in soil around plant bases, and reduced adult emergence of target pests in subsequent weeks. The nematode does not infect plants, mammals, fish, or non-target beneficial insects — making it one of the safest biocontrol agents available.
🩹 Treatment
- No treatment needed — this is a beneficial biocontrol agent. Apply commercially reared infective juveniles (IJs) at 1–2 billion/ha as a soil drench in the evening (UV sensitivity requires evening application) at 500–1000 L water/ha, or via drip irrigation in polyhouse and orchard crops. Maintain soil moisture at field capacity for 7–10 days after application — desiccation kills the nematodes. Apply during the target pest's most vulnerable life stage (typically larval stages in the top 10 cm of soil).
🌿 Organic treatments
- Soil drench with H. indica infective juveniles @ 1–2 billion IJs/ha in 500–1000 L water; application via drip irrigation in polyhouse crops; application as a root-dip in nursery seedlings @ 1 million IJs/L for 30 minutes before transplanting; tank-mix with sticker (0.1 % agar or 0.05 % xanthan gum) to prolong survival on foliage; repeated applications every 4–6 weeks during the pest's active season.
🧪 Chemical treatments
- No chemical treatment needed — beneficial agent. Compatible with most biological insecticides (Bt, NPV, azadirachtin) but incompatible with most chemical insecticides (organophosphates, carbamates, neonicotinoids) and most fungicides — apply separately with at least 7 days gap. Avoid tank-mixing with copper-based fungicides, mancozeb, or chlorpyrifos — all toxic to H. indica.
🛡️ Prevention
- No prevention needed — this is a beneficial biocontrol agent. To conserve naturally occurring populations: maintain soil organic matter above 1.5 % (apply FYM, compost, or green manure); avoid broad-spectrum soil-applied insecticides (chlorpyrifos, carbofuran, phorate) that kill both pest larvae and entomopathogenic nematodes; maintain soil moisture at field capacity during the dry season; use minimum-till or no-till practices to preserve nematode populations in the top 10 cm of soil; rotate with cover crops (sunhemp, horse gram) that support alternative insect hosts and sustain nematode populations between crops.
🪴 Affected plants
- Polyphagous biocontrol agent that infects and kills soil-dwelling insect larvae including white grubs (Holotrichia spp., Leucopholis spp.), root weevils (Myllocerus spp.), cutworms (Spodoptera litura), stem borers (Chilo partellus, Sesamia inferens), and fruit flies (Bactrocera spp.). Used in India against white grubs in sugarcane, groundnut, and vegetables; against root weevils in cardamom, tea, and coffee; and against fruit fly pupae in mango and cucurbits.
🦋 Natural predators
- As a biocontrol agent, H. indica has few significant natural enemies. Predatory mites (Mesostigmata), springtails (Collembola), and nematode-trapping fungi (Arthrobotrys spp.) occasionally prey on free-living IJs in soil; certain soil bacteria (Pseudomonas spp., Bacillus spp.) produce antibiotics toxic to the symbiotic Photorhabdus.
🌱 Host plants
- Polyphagous biocontrol agent — does not feed on plants. Used against soil-dwelling insect larvae in sugarcane, groundnut, vegetables, cardamom, tea, coffee, mango, cucurbits, and many other crops.
🔄 Lifecycle
- Infective juveniles (IJs) seek insect hosts in soil; IJs enter host through natural openings and release symbiotic bacterium Photorhabdus luminescens; bacterium kills host within 24–48 hours; nematodes feed on bacterium-digested host tissues, complete 2–3 generations inside cadaver; new IJs emerge from spent cadaver to seek new hosts.
- Total lifecycle 7–14 days inside host at 28°C; IJs survive 3–6 months in soil without a host.
📅 Season
- Active year-round in moist tropical Indian soils; application efficacy peaks during the warm humid months (June–November) when soil moisture is favourable and target pest larvae are active in the top 10 cm of soil.
🔎 Appearance
- Infective juveniles (IJs) are microscopic, transparent, non-feeding, free-living third-stage nematodes (~0.5–1.0 mm long) that actively seek out insect hosts in soil.
- Adult males and females of H.
- indica are hermaphroditic in the first generation and sexually dimorphic in subsequent generations, with females reaching 2–5 mm length.
- The symbiotic bacterium Photorhabdus luminescens, carried in the nematode's gut, gives infected insect larvae a characteristic orange-red to brick-red colour and — in freshly killed larvae — a faint luminescence visible in darkness.
💥 Damage level
- Beneficial
🔁 Reproduction rate
- Fast
🗺️ Geographic regions
- Indian Subcontinent (pan-India
- native to Indian soils — first described from Tamil Nadu)
- pantropical and warm-temperate through biocontrol deployment.
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