Chapter 2: Biology of Knapweed Biocontrol Agents
From Bugwoodwiki
Wilson, L.M. and Randall, C.B. 2005. Biology and Biological Control of Knapweed. USDA Forest Service FHTET-2001-07. 3rd Edition. 110 p.
Biological control of knapweeds is one of the oldest classical biocontrol programs in the United States and Canada. It began in the 1960’s with the importation of two seedhead flies: the knapweed banded gall fly, Urophora affinis, and the UV knapweed seedhead fly, U. quadrifasciata. In all, 16 agents have been introduced; of these, 13 are insect species, two are fungi, and one is a mite (not released). Only the insects are emphasized in this manual because they are by far the most widespread, readily available and easy to work with. This chapter is organized into two sections: seedhead-feeding (seedhead feeders) and root-boring (root borers) insects.
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Basic Insect Biology
Insects are a diverse and complicated group of animals. Basic knowledge of insect anatomy and lifecycles will help a great deal in recognizing knapweed bioagents in the field and understanding their impact on the weed. Adult insects possess unique characteristics: 1) an exoskeleton, 2) a segmented body consisting of three regions (head, thorax and abdomen), and 3) three pairs of legs (Fig. 10).
Insects grow and develop through a series of stages. The transformation from egg through juvenile stages to adult is called metamorphosis. This process can be incomplete or complete. All the insects used in biocontrol of knapweed undergo complete metamorphosis (having four distinct life stages): egg, larva (of which there can be three or more instars), pupa, and finally, adult.
The insect bioagent’s lifecycle (Fig. 11) is closely matched, or synchronized, with knapweed’s. In fact, in order to qualify as an acceptable biological control agent, the insect must show that it eats and develops only on knapweed and no other plants. Without knapweed, or a specific complex of knapweed, the insect will die. This highly specific, tightly regulated insect-plant relationship is the most critical issue in classical biological control of knapweeds.
Insects and Knapweed
Three types of insects are used in biocontrol of knapweed: flies, moths and beetles. In all, 13 species of insects, occurring in the seedheads or roots, are discussed in this manual (Table 1). All four fly species are ‘fruit flies’ (Family Tephritidae), in that they occur in the seedheads where the larvae eat developing flowers and seeds. One moth species and three weevil species complete the complex of eight seed-feeding bioagents on knapweed (Fig. 12). Among the root borers are three moth species and two beetle species. One beetle, Cyphocleonus achates, is a weevil, and the other beetle, Sphenoptera jugoslavica, is a metallic wood borer.
All of the insect bioagents damage knapweed plants as larvae by feeding internally in the seedheads or roots. In general, adults have little impact on the plant except for two of the seedhead weevils, Larinus minutus and L. obtusus. Adults of these weevils can significantly defoliate knapweed stems, further weakening the plant.
Table 1 lists the natural enemies of knapweeds in the United States and the species of knapweed they attack.
It is unlikely that any one of these species alone could successfully control knapweed. Most knapweed biocontrol programs use a combination of bioagents which together create multiple stresses on the plant and have a greater chance of contributing to the suppression of knapweed.
Table 1. Knapweed bioagents established in the United States and the species of knapweeds they attack.
| Insects | Insects | Insects | Knapweeds | Knapweeds | Knapweeds | Knapweeds | Knapweeds | Knapweeds |
|---|---|---|---|---|---|---|---|---|
| Type | Type | Species | Spotted | Diffuse | Squarrose | Meadow | Black | Brown |
| Seedhead Feeders | Flies | Urophora affinis | • | • | • | |||
| Seedhead Feeders | Flies | Urophora quadrifiasciata | • | • | • | • | • | • |
| Seedhead Feeders | Flies | Terellia virens | • | • | ||||
| Seedhead Feeders | Flies | Chaetorellia acrolophi | • | • | • | |||
| Seedhead Feeders | Moth | Metzneria paucipunctella | • | • | • | |||
| Seedhead Feeders | Beetles | Larinus minutus | • | • | • | • | ||
| Seedhead Feeders | Beetles | Larinus obtusus | • | • | • | • | ||
| Seedhead Feeders | Beetles | Bangasternus fausi | • | • | • | • | ||
| Root Borers | Moths | Agapeta zoegana | • | • | • | |||
| Root Borers | Moths | Pelochrista medullana | • | • | ||||
| Root Borers | Moths | Pterolonche inspersa | • | • | ||||
| Root Borers | Beetles | Cyphocleonus achates | • | • | ||||
| Root Borers | Beetles | Sphenoptera jugoslavica | • | • |
Identifying Insects
An important part of any successful biocontrol program is the ability to identify bioagents in the field. As adults, bioagents are relatively easy to identify with their variable size, color, and habits. Identifying the larvae is more challenging than the adults – and yet probably more important to know because it is in the larval stage that the bioagents: 1) do the most damage, 2) are often monitored in the field, and 3) provide conclusive evidence that the insects are established in the field.
Figure 13 is a key for identifying, in three easy steps, the larva of a fly, a moth and a beetle. This key is specific to knapweed insects, not insect larvae in general.
Fly larvae have no head capsules whereas beetle and moth larvae do. Fly larvae are sometimes confused with other larvae because they appear to have a broad, dark head. This is actually a dark, hardened anal plate anchoring the spiracles (breathing orifices).
Moth larvae have both head capsules and prolegs.
Beetle larvae are more variable. Weevil larvae (called grubs) are white, C-shaped, and have head capsules but no abdominal prolegs. Metallic wood boring larvae are narrow and tapering, with wide, somewhat flattened heads.
Figure 14 is a key for identifying the pupa of a beetle, a moth and a fly.
Beetle pupae have well-developed appendages that are obviously not fused to the pupal body.
Moth pupae have moderately well-developed appendages fused to the body.
Fly pupae are contained inside a barrel-shaped puparium.
Seedhead Feeders
There are eight different seedhead-feeding insect species for controlling knapweeds that are established in the United States and Canada (Table 2). Among the seedhead-feeding insects are four fly, one moth, and three beetle species. The fly, Urophora affinis, was the first insect to be introduced into the United States and Canada for the biological control of diffuse and spotted knapweed. The second Urophora species, U. quadrifasciata, was not approved for release in the United States because of taxonomic concerns, but nevertheless migrated to the United States after being released in Canada. Two other flies are Chaetorellia acrolophi and Terellia virens (Fig. 15). Another seedhead feeder is the seedhead moth, Metzneria paucipunctella. Among the beetles are two closely related weevils, Larinus minutus and L. obtusus. The other seedhead weevil is Bangasternus fausti.
All of the seedhead-feeding insects damage the plant when larvae consume immature seeds and other tissues in the flower head, or capitulum. Feeding by the insects sometimes causes the plant to encase the insect larva in a hard or soft gall-like structure. In forming these galls, the insect is draining valuable nutrients away from normal plant growth (referred to as a metabolic sink), further depleting the plant’s limited resources. Gall-forming insects are well adapted to plants like the knapweeds that produce a large number of small seedheads throughout the growing season.
Gall formers (the two Urophora flies) feed on actively dividing cells so they attack at the early stages of seedhead bud formation. The maximum number of gall-forming insect larvae in a seedhead is limited by the size of the seedhead, not the amount of food.
The impact that gall formers have on a plant is dictated by:
- Abundance of galls
- Power of galls as a metabolic sink
- Favorable weather conditions (i.e. drought, cold)
The other seedhead-feeding species either do not form a gall or construct a chamber in which to feed (Fig. 16). They inflict direct damage on developing seeds but do not create a metabolic sink.
Seedhead feeders are separated in time and space by such factors as:
- Type of knapweed patches insects will infest (isolated plants vs. dense stands)
- Larval feeding habits (e.g., feeding in the receptacle, florets, and seeds)
- Number of generations per year
- Number of larvae in the head
- Overwintering site (in or out of the seedhead)
Species of Seedhead Feeders
- Urophora affinis
- Urophora quadrifiasciata
- Terellia virens
- Chaetorellia acrolophi
- Metzneria paucipunctella
- Larinus minutus
- Larinus obtusus
- Bangasternus fausi
Timeline of Attack
Knapweeds produce flower heads throughout the spring and summer, creating a constant supply of seedheads of different sizes and stages of development for the seedhead feeding insects to utilize.
Figure 15 is a comparison of adult U. affinis, U. quadrifasciata, C. acrolophi and T. virens.
Each seedhead-feeding insect prefers certain seedhead characteristics for oviposition (see Table 3). Figure 16 shows U. affinis ovipositing into knapweed flower bud and the position of its eggs. Figure 17 compares the galls of U. affinis and U. quadrifasciata. Figures 18 and 19 depict the position of fly, beetle and moth larvae inside the knapweed seedhead.
More than one bioagent can occupy a seedhead at one time. This coexistence is possible because of specialized adaptations.
Bioagents with a short adult life span attack fewer seedheads. Long-lived adults can attack many seedheads during their life span. Agents with more than one generation per year can attack seedheads during two distinct periods in the growing season.
Table 4 is a summary description of knapweed seedhead feeders. Table 5 compares the lifecycle of seedhead flies with the lifecycle of knapweed. Table 6 compares the lifecycle of seedhead moths and beetles with the growth stages of knapweeds.
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Table 2. List of seedhead feeding knapweed biocontrol agents.
| Type | Scientific Name | Common Name |
|---|---|---|
| Fly | Urophora affinis | Banded knapweed gall fly
UV knapweed seedhead fly Green clearwing fly, verdant seed fly Knapweed peacock fly |
| Moth | Metzneria paucipunctella | Spotted knapweed seedhead moth |
| Beetle | Larinus minutus | Lesser knapweed flower weevil
Blunt knapweed flower weevil Broad-nosed knapweed seedhead weevil |
Table 3. Knapweed seedhead size and stage of development preferred by each of the eight seedhead feeding biocontrol agents.
| Seedhead Development | Seedhead Feeder |
|---|---|
| Closed seedhead buds
0.12 inch (3mm) in diameter | Urophora affinis (spring only) |
| Seedhead buds
0.14 to 0.2 inch (4 to 5 mm) inch in diameter | Bangasternus fausi (spring only)
Chaetorellia acrolophi (first generation spring; second generation summer) |
| Seedhead buds
0.2 to 0.3 inch (5 to 7 mm) in diameter | Urophora quadrifiasciata (spring, non-obligatory second generation summer)
Chaetorellia acrolophi(first generation spring; second generation summer) |
| Late seedhead bud to early bloom | 'Metzneria paucipunctella(spring only) |
| Full bloom | Terellia virens (spring flowers, if a second generation will affect attack later summer flowers) |
| Early seed formation | Larinus minutus and Larinus obtusus (adults persist for a number of weeks in the summer and lay eggs into into susceptible seedheads as they become available) |
Table 4. Summary description of knapweed seedhead feeders.
| Agent | Flies | Flies | Flies | Flies | Moth | Beetles | Beetles | Beetles |
|---|---|---|---|---|---|---|---|---|
| Agent | Urophora affinis | Urophora quadrifiasciata | Terellia virens | Chaetorellia acrolophi | Metzneria paucipunctella | Larinus minutus | Larinus obtusus | Bangasternus fausi |
| Number of Generations | One, partial second | One or two | One, partial second | Two, rarely three | One | One | One | One |
| Adults | Black, faint horizontal bands on wings | Black, dark bands form a "UV" pattern on wings | Clear-winged with yellow or greenish bodies | Dark bodied with yellow bands on body and wings | Gray wings folded over back when at rest, dark spots on wings | Grayish black with large snout, reddish brown wings | Black, slightly mottled, bulbous snout, black legs | Grayish black, with blunt snouts |
| Eggs | 0.2" (5mm) long | 0.2" (5mm) long | 0.2" (5mm) long | 0.2" (5mm) long | 0.3' (7mm) long | 0.2" (5mm) long | 0.2-0.3" (5-7mm) long | 0.2" (5mm) long |
| Eggs | Cluster of 1-5 young inside unopened seedheads | Singly among developing florets | Multiple eggs laid inside the open flower head | Singly or in small clusters under bracts of flower bud | Singly on bracts at base of flower bud | Clusters are laid in the bud between pappus hairs | Singly into a newly opened head | Singly on bracts or stem leaves covered with a black egg cap |
| Larvae | Creamy white, barrel-shaped, retracted head, circular dark brown anal plate | Creamy white, barrel-shaped, retracted head, elliptical dark brown anal plate | Barrel-shaped white, turning yellow brown | Barrel-shaped, 1st gen. white, 2nd gen. yellow | White with dark brown head capsule, five pair of prolegs | White legless C-shaped grub with brown head capsule | White legless C-shaped grub with brown head capsule | White legless C-shaped grub with brown head capsule |
| Pupae | Inside woody gall, brown; 0.06" long | Inside papery gall, brown; 0.06" long | No gall, yellow-brown puparium; 0.06" long | No gall, white puparium covered in pappus hairs | Cocoon brown appendages fused to body | Long, white turning brown before emergence | Long, white turning brown before emergence | In a chamber in head, white (brown before emergence) |
| Overwinter | Larvae in seedhead | Larvae in seedhead | Larvae in seedhead | Larvae in seedhead | Larvae in seedhead | Adult in litter near root | Adult in litter near root | Adult in litter near root |
Table 5. Comparison of seedhead fly lifecycles by knapweed growth stage.
| Urophora affinis | Urophora quadrifiasciata | Terellia virens | Chaetorellia acrolophi | |
|---|---|---|---|---|
| Knapweed attacked | Spotted, Diffuse, Squarrose | Spotted, Diffuse, Brown, Black, Meadow, Squarrose | Spotted, Diffuse | Spotted, Diffuse, Squarrose |
| Seedling | Overwinters as larvae in previous year's seedheads | Overwinters as larvae or pupae in previous year's seedheads | Overwinters as mature larvae or pupae in previous year's seedheads | Overwinters as larvae in previous year's seedheads |
| Rosette | Overwinters as larvae in previous year's seedheads | Overwinters as larvae or pupae in previous year's seedheads | Overwinters as mature larvae or pupae in previous year's seedheads | Overwinters as larvae in previous year's seedheads |
| Bolting | Late instar larvae and pupae | Late instar larvae and pupae | Adults emerge. Mating and egg laying begin with the onset of hot, sunny weather and continues for 4 to 6 weeks | Overwinters as larvae in previous year's seedheads |
| Early Flower Buds | Adults emerge and mate.Females lay eggs on young flower buds. | Adults emerge and mate. | Adults emerge.Mating and egg laying begin with the onset of hot, sunny weather and continues for 4 to 6 weeks | Adults emerge and mate. Females lay eggs into flower buds. |
| Late Flower Buds | Larvae feed in developing seedheads.Feeding leads to development of hard, woody galls. Severely infested buds do not flower. | Egg laying between bracts of developing flower buds. | Eggs are laid in young, opening flowers.Eggs hatch in 3 to 5 days. Larvae feed for up to 14 days.Second generation may occur. | Larvae emerge from eggs and tunnel to center of flower bud.Larvae pupate 10 to 20 days after hatch, producing a second generation.A third generation is possible, but rare. |
| Flowering | Larvae feed in developing seedheads.Feeding leads to development of hard, woody galls.Severely infested buds do not flower. | Eggs hatch and only develop in pollinated seedheads or those attacked by U. affinis.Feeding leads to formation of thin, papery gall. | Eggs are laid in young, opening flowers. Eggs hatch in 3 to 5 days.Larvae feed for up to 14 days. Second generation may occur. | Larvae emerge from eggs and tunnel to center of flower bud.Larvae pupate 10 to 20 days after hatch, producing a second generation.A third generation is possible, but rare. |
| Seed Formation | Larvae feed in developing seedheads.Feeding leads to development of hard, woody galls.Severely infested buds do not flower. | Eggs are laid in young, opening flowers. Eggs hatch in 3 to 5 days.Larvae feed for up to 14 days.Second generation may occur. | ||
| Mature | 10 to 33% of larvae pupate and emerge for a second generation in late forming seedheads.Majority overwinter as larvae in seedheads. | If a second generation occurs, adults emerge and lay eggs in susceptible seedheads.Second generation overwinters as larvae in seedheads. | First generation larvae overwinter as pupa, second generation larvae overwitner as prepupae; pupation occurs following spring. | Larvae from second (possible third) generation feed upon mature seed. |
| Senescence | 10 to 33% of larvae pupate and emerge for a second generation in late forming seedheads. Majority overwinter as larvae in seedheads. | If a second generation occurs, adults emerge and lay eggs in susceptible seedheads. Second generation overwinters as larvae in seedheads. | First generation larvae overwinter as pupa, second generation larvae overwitner as prepupae; pupation occurs following spring. | Larvae from second (possible third) generation feed upon mature seed. |
Table 6. Comparison of seedhead moth and weevil lifecycles by knapweed growth stage.
| Metzneria paucipunctella | Bangasternus fausi | Larinus minutus | Larinus obtusus | |
|---|---|---|---|---|
| Knapweed attacked | Spotted, Diffuse, Meadow | Spotted, Diffuse, Squarrose, Meadow | Spotted, Diffuse, Squarrose, Meadow | Spotted, Diffuse, Squarrose, Meadow |
| Seedling | Overwinters as larvae in previous year's seedheads | Overwinters as adults in plant litter and soil surrounding plant. | Overwinters as adults in plant litter and soil surrounding plant. | Overwinters as adults in plant litter and soil surrounding plant. |
| Rosette | Overwinters as larvae in previous year's seedheads | Overwinters as adults in plant litter and soil surrounding plant. | Overwinters as adults in plant litter and soil surrounding plant. | Overwinters as adults in plant litter and soil surrounding plant. |
| Bolting | Mature larvae, and pupae | Adults begin to emerge. | Adults become active feeding on leaves, including seedlings and rosettes. | Adults become active feeding on leaves, including seedlings and rosettes. |
| Early Flower Buds | Mature larvae, and pupae | Adults feed on foliage, mate, lay eggs on bracts or on end of a stem. | Adults become active feeding on leaves, including seedlings and rosettes. | Adults become active feeding on leaves, including seedlings and rosettes. |
| Late Flower Buds | Adults emerge and mate, lay eggs on bracts at base of young flower heads or on stem below flower head. | Eggs hatch and larvae migrate to center of flower bud. Feed on developing florets and ovules. | Adults become active feeding on leaves, including seedlings and rosettes. | Adults become active feeding on leaves, including seedlings and rosettes. |
| Flowering | Eggs hatch and larvae enter opened flower head, feed on florets. | Larvae complete development from egg to adult in 32 days. Adults emerge from seedhead leaving a characteristic emergence hole. Overwinter in litter and soil surrounding plant. | Mating begins. | Mating begins. |
| Seed Formation | Larvae mine in flower base (receptacle) and feed on seeds. Overwinter as larvae in the seedhead. | Larvae complete development from egg to adult in 32 days. Adults emerge from seedhead leaving a characteristic emergence hole. Overwinter in litter and soil surrounding plant. | Eggs laid between pappus hairs. | Eggs laid between pappus hairs. |
| Mature | Larvae mine in flower base (receptacle) and feed on seeds. Overwinter as larvae in the seedhead. | Larvae complete development from egg to adult in 32 days. Adults emerge from seedhead leaving a characteristic emergence hole. Overwinter in litter and soil surrounding plant. | Larvae hatch, feed on pappus hairs then move down to seeds and receptacle. | Larvae hatch, feed on pappus hairs then move down to seeds and receptacle. |
| Senescence | Larvae mine in flower base (receptacle) and feed on seeds. Overwinter as larvae in the seedhead. | Larvae complete development from egg to adult in 32 days. Adults emerge from seedhead leaving a characteristic emergence hole. Overwinter in litter and soil surrounding plant. | Pupate and emerge through exit holes; move to overwintering site. | Pupate and emerge through exit holes; move to overwintering site. |
Root Borers
There are five root boring insect species established in the United States and Canada for the control of diffuse, spotted and squarrose knapweeds. Three species are moths (sulfur knapweed root moth, Agapeta zoegana; gray-winged knapweed root moth, Pelochrista medullana, and brown-winged knapweed root moth, Pterolonche inspersa), and two are beetles (knapweed root weevil, Cyphocleonus achates, and bronze knapweed root borer, Sphenoptera jugoslavica). All these insects can be present in the root at the same time. Studies are underway to determine how these insects coexist and compete in knapweed roots.
All five root-feeding insects damage the plant in the larval stage by feeding on the central vascular tissue or the cortex of the root just below the epidermis, depending on species (Fig. 34). Eggs are laid on the stem, on the basal rosette leaves, on the soil surface, or on the root crown just below the soil surface. Upon emerging from the eggs, larvae immediately burrow into the root, where they feed and complete their development.
As larvae, insects mine the roots depleting the carbohydrate reserves of the plant that are important for growth and essential for overwintering. In addition to mining the roots, beetle larvae of S. jugoslavica, C. achates and P. inspersa cause root galls. Galls create a metabolic sink, meaning that the energy generated by the plants through photosynthesis is used to produce the gall rather than to meet critical plant needs.
All the insects are univoltine, which means they produce only one generation per year. Most larvae complete their development in a single root; however, larvae of the sulfur root moth, Agapeta zoegana, can migrate a short distance between roots during the growing season.
Species of Root Borers
- Agapeta zoegana
- Pterolonche inspersa
- Pelochrista medullana
- Cyphocleonus achates
- Sphenoptera jugoslavica
Table 7. Summary description of knapweed root borers.
| Agent | Moth | Moth | Moth | Beetle | Beetle |
|---|---|---|---|---|---|
| Agapeta zoegana | Pterolonche inspersa | Pelochrista medullana | Cyphocleonus achates | Sphenoptera jugoslavica | |
| Number of Generation | One | One | One | One | One |
| Adults | Bright yellow moth with brown wing bands | Light brown moth with tan-colored wings | Tan to gray with mottled wings | Large, mottled gray color | Bronze metallic-colored, elongate and flattened |
| Adults | 0.44: (11mm) long | 0.8" (2cm) long | 0.3" (8mm) long | 0.4-0.6" (30-40mm) long | 0.4" (10mm) long |
| Lifespan | 11 to 14 days | About 15 days | 2 weeks | 10 weeks | 12 weeks |
| Eggs | Eggs are white turning orange, round and ribbed, laid singly or in groups of 2-3 in stem and leaf crevices. | Eggs are oval and black, laid singly or in groups of 2-3 on underside of leaf. | Eggs are oval, white and flattened, and ribbed. Laid singly or in small batches on the underside of leaf surface. | Eggs are oval and cream-colored, laid in batches on the root crown, just below the soil surface. | Eggs are oval, flattened, white turning bluish-black, laid on the base of one rosette leaf petiole. |
| Larvae | Larvae are white and have brown head capsule and legs. | Legs are elongate, pale and have head capsule and legs. Found in a silken cocoon. | Larvae are elongate, pale and have head capsule and legs. Found in a mined tunnel in silken web. | Larvae are large, C-shaped grubs located inside a gall in the center of the root. 0.1" (2.5mm) long. | Larvae are cylindrical, tapering at the tail end. 0.4" (10mm) long |
| Pupae | Large, white, appendages fused to body. | Large, white, appendages fused to body. | Large, white, appendages fused to body. | Large, white with free appendages. | Large cream colored with free appendages. |
| Overwinter | Mature larvae in the root. | Mature larvae in the root. | Mature larvae in the root. | Mature larvae in the root. | Mature larvae in the root. |
Table 8. Comparison of knapweed root borer lifecycles by knapweed growth stage.
| Agapeta zoegana | Pterolonche inspersa | Pelochrista medullana | Cyphocleonus achates | Sphenoptera jugoslavica | |
|---|---|---|---|---|---|
| Knapweeds Attacked | Spotted, Diffuse, Squarrose | Spotted, Diffuse | Spotted, Diffuse | Spotted, Diffuse, Squarrose | Spotted, Diffuse, Squarrose |
| Seedling | Overwinters as larvae in previous year's roots. | Overwinters as larvae in previous year's roots. | Overwinters as larvae in previous year's roots. | Overwinters as larvae in previous year's roots. | Overwinters as larvae in previous year's roots. |
| Rosette | Overwinters as larvae in previous year's roots. | Overwinters as larvae in previous year's roots. | Overwinters as larvae in previous year's roots. | Overwinters as larvae in previous year's roots. | Overwinters as larvae in previous year's roots. |
| Bolting | Larvae pupate and new adults emerge. | Larvae pupate and new adults emerge. | Larvae pupate and new adults emerge. | Larvae pupate and new adults emerge. | Larvae pupate and new adults emerge. |
| Early Flower Buds | Larvae pupate and new adults emerge. | Larvae pupate and new adults emerge. | Larvae pupate and new adults emerge. | Larvae pupate and new adults emerge. | Larvae pupate and new adults emerge. |
| Late Flower Buds | Mating; eggs laid at base of basal leaves. | Larvae pupate and new adults emerge. | Larvae pupate and new adults emerge. | Larvae pupate and new adults emerge. | Larvae pupate and new adults emerge. |
| Flowering | Larvae hatch and chew into root cortex. | Adults mate and females lay eggs | Adults mate and females lay eggs | Adults mate and females lay eggs | Adults mate and females lay eggs |
| Seed Formation | May migrate to other nearby roots and continue development. | New larvae migrate to root vascular tissue. | New larvae migrate to root cortex. | Larvae burrow into root central vascular tissue, forming a gall in the root. | Larvae burrow into root central vascular tissue, forming a gall in the root. |
| Mature | Overwinter | Overwinter | Overwinter | Overwinter | Overwinter |
| Dissemination | Overwinter | Overwinter | Overwinter | Overwinter | Overwinter |
