Doppelgangers: Giant water bug vs Cockroach

Years ago, I was walking home from the University of Alberta campus on a September evening, watching the ground, as entomologists are wont to do, when I saw a huge insect on its back on the sidewalk. It was just off of a major crosswalk under a streetlight. Upon a quick glance, I knew it was one of two things: a giant water bug or a cockroach. Either way, I needed it for my collection, so I carefully collected it using the only container I had on hand. I say that I “carefully collected” it, because water bugs are known for their painful bite and I did not want to take any risks. From inside the container, it was clear that I had scooped up a water bug.

Giant water bugs (Lethocerus americanus) are true bugs (Hemiptera) that belong to the family Belostomatidae. There are over 150 species of water bugs in the Belostomatidae, but most are quite large (> 2 cm). Belostomatids are usually found in ponds, lakes, or slow moving rivers and streams. They spend most of their time in the water, but disperse between bodies of water by flying (except in species that have reduced wings and are flightless), at which time they may be found around streetlights or porchlights. They are predators of other insects, small fish, snails, amphibians, and other animals that they encounter in the water. Giant water bugs use their forelegs to capture prey and then use their long beak-like proboscis to feed on their prey. First, they inject enzymes into their prey that breakdown prey tissues into a liquid. Then they feast on a liquid lunch by sucking their victim dry. Their bite can be very painful. These ‘toe-biters’ are best avoided, but they are important beneficial insects in aquatic ecosystems.

Giant water bugs can be easily mistaken for adult cockroaches (especially the American cockroach, Periplaneta americana, Blattodea: Blattidae). Both water bugs and cockroaches have large, oval shaped bodies that are usually brown coloured. A casual glance or quick encounter with either may lead to a case of mistaken identity. But, upon closer examination, some key differences are easy to see:

  1. Cockroaches have long, obvious antennae. Water bugs do not appear to have antennae unless closely examined.
  2. The head and eyes of water bugs are visible from above. The head and eyes of cockroaches are hidden underneath the pronotum.
  3. Cockroaches have spiny legs evolved for running and quick movement. All six of their legs look the same. Water bugs have forelegs adapted to grabbing prey (raptorial legs). Their legs are also adapted for swimming and have no obvious spines.

Cockroaches are usually classified as pests by humans, but some provide important ecosystem services (i.e. they are decomposers) and others are television and movie stars (i.e. Madagascar hissing cockroaches).

Giant water bug
cc-by-nc 4.0 Christian Schwartz
American cockroach
cc-by-nc 2.0 K. Schneider

Doppelgangers may be related (e.g. same genus) or may not be related, as in the case of monarch butterflies (Danaus plexippus) and viceroys (Limenitis achrippus).  Doppelgangers are usually relatively harmless but sometimes the doppelganger is a pest yet their behaviour, lifecycle or hosts may be different.

Correctly identifying a pest enables selection of the most accurate scouting or monitoring protocol. Identification and monitoring enables the application of economic thresholds. It also enables a producer to select and apply the most effective control option(s) including method and timing of application.  For the rest of the growing season, the Insect of the Week will feature insect crop pests and their doppelgangers.

The case of the innocuous versus the evil twin
When making pest management decisions, be sure that the suspect is actually a pest. This can be challenge since insects often mimic each other or look very similar. An insect that looks, moves and acts like a pest may in fact be a look-alike or doppelganger.

Review previously featured insects by visiting the Insect of the Week page.

Doppelgangers: Hoverflies vs. bees vs. yellow jacket wasps

Hoverflies are un-BEE-lievably good mimics of bees and yellow jacket wasps!

Mimicry is used by insects in several ways.
Some insects, like the ambush bug and praying mantis, look like plants. These predators sit very still, blending into their surroundings, and wait very patiently for their unwitting prey to pass by. Other insects, use mimicry to avoid predation, often by taking on the appearance of species with clear markings that are known to be dangerous. Hoverflies (Diptera: Syrphidae) are some of the most convincing mimics of all of the insects. Even experts can have a difficult time distinguishing hoverflies from bees and wasps, especially when working in the field.

Bees (honeybees, solitary bees, native bees; Hymenoptera: Apidae): Bees are important pollinators, usually with distinctive black and yellow strips. Bees have two pairs of wings and are much fuzzier than wasps or hoverflies. Bees have stingers, but are not aggressive under normal circumstances. Some species of bees (e.g. honeybees) have barbed stingers that become lodged inside their victim. When this happens, the stinger is pulled out of the body of the bee and the bee dies. For this reason, bees with barbed stingers only sting as a last resort, in an effort to protect their colony. Bees are beneficial insects that will leave you alone if you leave them alone.

Honeybee
cc-by 2.0 Renee Grayson

Yellow jacket wasps (Hymenoptera: Vespidae): Yellow jackets and some of their close relatives have colouring similar to bees. Like bees, wasps have two pairs of wings. Unlike bees, which are usually vegetarians, wasps are carnivores that eat other insects. Thus, wasps are beneficial insects, but they also have a bad reputation for harming people because they scavenge for food at our picnics and barbecues during the summer. Wasps also tend to be aggressive and will sting with little provocation.

Yellow jacket wasp
cc-by-nc-nd 2.0 Bryan Jones

Hoverflies (Diptera: Syrphidae): Hoverflies belong to a completely different order of insects than bees and wasps. Like bees, hoverflies are pollinators and are often observed hovering over flowering plants in fields and gardens. Unlike bees and wasps, hoverflies only have one pair of wings. Hoverflies do not have a stinger. They also do not have biting mouthparts, so they can do no harm to people. Hoverflies protect themselves from predators, and people, by mimicking bees and wasps. In addition to pollinating plants, hoverflies provide another important ecosystem service: their larvae are predators of small plant-dwelling insects like aphids!

Syrphid fly
cc-by-nc-sa 2.0 Eero Sarkkinen

The case of the innocuous versus the evil twin: When making pest management decisions, be sure that the suspect is actually a pest. This can be challenge since insects often mimic each other or look very similar. An insect that looks, moves and acts like a pest may in fact be a look-alike or doppelganger.

Doppelgangers may be related (e.g. same genus) or may not be related, as in the case of monarch butterflies (Danaus plexippus) and viceroys (Limenitis achrippus).  Doppelgangers are usually relatively harmless but sometimes the doppelganger is a pest yet their behaviour, lifecycle or hosts may be different.

Correctly identifying a pest enables selection of the most accurate scouting or monitoring protocol. Identification and monitoring enables the application of economic thresholds. It also enables a producer to select and apply the most effective control option(s) including method and timing of application.  For the rest of the growing season, the Insect of the Week will feature insect crop pests and their doppelgangers.

Review previously featured insects by visiting the Insect of the Week page.

Contributed by Dr. Meghan Vankosky (@vanbugsky). 

Monarch vs. Painted Lady

The case of the Monarch butterfly vs. Painted Lady butterfly (also Viceroy butterfly) An orange butterfly fluttered by. Was it a Monarch butterfly (Danaus plexippus)? Or a Painted Lady butterfly (Vanessa cardui)? If it’s a Monarch, it is species of Special Concern listed under the Species at Risk Act and is not a crop pest. Instead, it’s larvae feed solely on milkweed (Asclepias spp.), typically found in wetland areas. Painted Lady larvae, on the other hand, feed on a wider range of plants including sunflower, canola, mustard, borage, soybean, Canada thistle, burdock, knapweed, wormwood and many other plant species. While neither species overwinter in Canada, Monarchs have regular migratory routes into Canada from Mexico through the USA; Painted Ladies are accidental tourists that are on occasion blown up from the US. One important distinguishing characteristic is the distinct black band with white dots that outline the wings of Monarchs. Painted Ladies do not have this band; instead they have thin white markings along the scalloped wing edges.

Monarch butterfly (Danaus plexippus)
cc by sa 3.0 Kenneth Dwain Harrelson
Painted Lady butterfly (Vanessa cardui)
cc by 3.0 Jean-Pol Grandmont
Viceroy butterflies (Limenitis archippus)
cc by 2.0 Benny Mazur

Viceroy butterflies (Limenitis archippus) are even more difficult to tell from Monarchs. Viceroys are smaller than Monarchs and sport a black line running through the middle (side-to-side) of the hindwing. Like the Monarch, Viceroys are not crop pests as their larvae feed exclusively on trees of the willow family (willow, poplar, cottonwood). For more information about Painted Lady butterflies, see the Insect of the Week page and our posts on the annual Monarch butterfly migration.  The case of the innocuous versus the evil twin: When making pest management decisions, be sure that the suspect is actually a pest. This can be challenge since insects often mimic each other or look very similar. An insect that looks, moves and acts like a pest may in fact be a look-alike or doppelganger.

Doppelgangers may be related (e.g. same genus) or may not be related, as in the case of monarch butterflies (Danaus plexippus) and viceroys (Limenitis achrippus).  Doppelgangers are usually relatively harmless but sometimes the doppelganger is a pest yet their behaviour, lifecycle or hosts
may be different.

Correctly identifying a pest enables selection of the most accurate scouting or monitoring protocol. Identification and monitoring enables the application of economic thresholds. It also enables a producer to select and apply the most effective control option(s) including method and timing of application. For the rest of the growing season, the Insect of the Week will feature insect crop pests and their doppelgangers.

Review previously featured insects by visiting the Insect of the Week page.

Insect of the Week: Doppelgangers: Lygus bugs nymphs vs. aphids

The case of lygus bug nymphs versus aphids: Small, green, soft-bodied, sucking insects – at first glance they could be either lygus bug nymphs or aphids. But spend a moment and look for the following characteristics, and you’ll be able to tell which pest you are dealing with.

  • Size: depending on the species, aphids can reach up to 4 mm long, but most will be 1-2 mm. Lygus bug nymphs will be larger, 4-6 mm long
  • Cornicles (small upright backward-pointing tubes found on the back side at the rear of abdomen): aphids have them, lygus bug nymphs do not. In some aphid species, the cornicles or where they attach to the abdomen are black (e.g. corn aphid, English grain aphid).
  • Markings: older lygus bug nymphs have five distinct black dots on their thorax and abdomen; aphids do not.  

For more information about these species and more tips on telling them apart, see our Insect of the Week page! Also, see our Monitoring protocols for lygus bugs in canola

Tarnished plant bug nymph – note five black dots on thorax and abdomen – Scott Bauer, USDA
English grain aphid – adult and nymphs – note black cornicles (tubes) sticking out the back – Tyler Wist, AAFC

The case of the innocuous versus the evil twin: When making pest management decisions, be sure that the suspect is actually a pest. This can be challenge since insects often mimic each other or look very similar. An insect that looks, moves and acts like a pest may in fact be a look-alike or doppelganger.

Doppelgangers may be related (e.g. same genus) or may not be related, as in the case of monarch butterflies (Danaus plexippus) and viceroys (Limenitis achrippus).  Doppelgangers are  usually relatively harmless but sometimes the doppelganger is a pest yet their behaviour, lifecycle or hosts may be different.

Correctly identifying a pest enables selection of the most accurate scouting or monitoring protocol. Identification and monitoring enables the application of economic thresholds. It also enables a producer to select and apply the most effective control option(s) including method and timing of application.  For the rest of the growing season, the Insect of the Week will feature insect crop pests and their doppelgangers.

Review previously featured insects by visiting the Insect of the Week page.

Insect of the Week: Doppelgangers: Lygus bug vs. Alfalfa plant bug

The case of lygus bug versus the alfalfa plant bug: It is easy to understand why lygus bugs (Lygus spp.) and alfalfa plant bugs (Adelphocoris lineolatus) are difficult to tell apart as they are closely related, belonging to the same family (Hemiptera: Heteroptera). They are similar in appearance (long narrow body) with the alfalfa bug being slightly longer. Adult lygus bugs have a distinctive triangular or “V”-shaped marking in the upper centre of the their backs and membranous wingtips. The alfalfa plant bug has a similar marking but it is less distinct. One difference between the two is that lygus bug nymphs have five black dots over their thorax and abdomen which alfalfa bug nymphs lack.

Another difference is that lygus bugs have a broader host range that includes canola, alfalfa, soybean, sunflower, strawberry and several other crops. Alfalfa bugs have a much more particular palette and are mainly found in alfalfa crops and only occasionally feed on red and yellow sweet clover or canola when alfalfa is in short supply.

For more information about these species and more tips on telling them apart, see our Insect of the Week page!

Tarnished plant bug (Lygus lineolaris) – cc-by Scott Bauer
Alfalfa plant bug (Adelphocoris lineolatus) – (c) Mike Dolinski. MikeDolinski@hotmail.com

The case of the innocuous versus the evil twin: When making pest management decisions, be sure that the suspect is actually a pest. This can be challenge since insects often mimic each other or look very similar. An insect that looks, moves and acts like a pest may in fact be a look-alike or doppelganger.

Doppelgangers may be related (e.g. same genus) or may not be related, as in the case of monarch butterflies (Danaus plexippus) and viceroys (Limenitis achrippus).  Doppelgangers are  usually relatively harmless but sometimes the doppelganger is a pest yet their behaviour, lifecycle or hosts may be different.

Correctly identifying a pest enables selection of the most accurate scouting or monitoring protocol. Identification and monitoring enables the application of economic thresholds. It also enables a producer to select and apply the most effective control option(s) including method and timing of application.  For the rest of the growing season, the Insect of the Week will feature insect crop pests and their doppelgangers.

Review previously featured insects by visiting the Insect of the Week page.

Insect of the Week – Doppelgangers: Grasshoppers

Bruner grasshopper (Melanoplus bruneri) adult. 
Photo credit: S. Barkley, Alberta Agriculture and Forestry.

The case of the prairie grasshoppers: There are 80 grasshopper species on the prairies but only a few that are considered pests. These include Packard (Melanopus packardii), clearwinged (Camnula pellucida), migatory (Melanopus sanguinipes), two-striped (Melanopus bivittatus) and Bruner Melanoplus bruneri) grasshoppers. They are recognizable as grasshoppers (similar body shape and distinctive large rear legs) and, depending on the species, range in size from 21 to 40 centimetres (8.25 to 15.75 inches). Most of these pest species can be distinguished by colouring and size. However, the Bruner and migratory grasshoppers are difficult to tell apart, needing to rely on examining the male genitalia (see Insect of the Week post from July , 2018).

For more information about grasshopper pests, see our Insect of the Week page!

Packard grasshopper – egg, nymph, adult
AAFC
Clearwinged grasshopper – egg, nymph, adult
AAFC
Migratory grasshopper – adult
Joseph Berger, Bugwood.org
Two-striped grasshopper – adult
John Gavloski, Manitoba Agriculture,
Food and Rural Development

More information related to the Bruner grasshopper:

See also:

Predicted grasshopper development (July 5, 2019)

Specific information about these grasshoppers, other pests and natural enemies can be found in the updated Field Crop and Forage Pests and their Natural enemies in Western Canada field guide.

The case of the innocuous versus the evil twin: When making pest management decisions, be sure that the suspect is actually a pest. This can be challenge since insects often mimic each other or look very similar. An insect that looks, moves and acts like a pest may in fact be a look-alike or doppelganger.

Doppelgangers may be related (e.g. same genus) or may not be related, as in the case of monarch butterflies (Danaus plexippus) and viceroys (Limenitis achrippus). Doppelgangers are  usually relatively harmless but sometimes the doppelganger is a pest yet their behaviour, lifecycle or hosts may be different.

Correctly identifying a pest enables selection of the most accurate scouting or monitoring protocol. Identification and monitoring enables the application of economic thresholds. It also enables a producer to select and apply the most effective control option(s) including method and timing of application.  For the rest of the growing season, the Insect of the Week will feature insect crop pests and their doppelgangers.

Review previously featured insects by visiting the Insect of the Week page.

Insect of the Week – Doppelgangers: Cereal leaf beetle vs. Collops beetles

The case of the innocuous versus the evil twin: When making pest management decisions, be sure that the suspect is actually a pest. This can be challenge since insects often mimic each other or look very similar. An insect that looks, moves and acts like a pest may in fact be a look-alike or doppelganger.

Doppelgangers may be related (e.g. same genus) or may not be related, as in the case of monarch butterflies (Danaus plexippus) and viceroys (Limenitis achrippus).  Doppelgangers are  usually relatively harmless but sometimes the doppelganger is a pest yet their behaviour, lifecycle or hosts may be different.

Correctly identifying a pest enables selection of the most accurate scouting or monitoring protocol. Identification and monitoring enables the application of economic thresholds. It also enables a producer to select and apply the most effective control option(s) including method and timing of application.  For the rest of the growing season, the Insect of the Week will feature insect crop pests and their doppelgangers.

The case of the cereal leaf beetle versus Collops beetles: 

Cereal leaf beetle, Boris Loboda

Cereal leaf beetles (Oulema melanopus), both adults and larva, feed on leaves (oat, barley, wheat, corn, etc), but it is the larval damage that can reduce yield and quality, especially if the flag leaf is stripped. Adults are 6-8 millimeters (.25-.31 inches) long with reddish legs and thorax (middle section between head and abdomen) and metallic bluish-black head and elytra (wing coverings).

Collops beetle, cc-by-nd-nc 1.0 Ashley Bradford

They may be confused with beneficial beetles belonging to the Collops genus (adults feed on aphids, stink bug eggs, moth eggs, small caterpillars, spider mites, whiteflies). Roughly the same size, they may have a red or orange thorax with/without red markings on their elytra, depending on the species. One consistent feature that will help distinguish between the two species is that the cereal leaf beetle elytra are smooth and shiny whereas the Collops’ elytra are covered in hairs.

Specific information on the cereal leaf beetle can be found in the updated Field Crop and Forage Pests and their Natural enemies in Western Canada field guide.

Review previously featured insects by visiting the Insect of the Week page.

Insect of the Week – Doppelgangers: midge vs. parasitoid

The case of the innocuous versus the evil twin: When making pest management decisions, be sure that the suspect is actually a pest. This can be challenge since insects often mimic each other or look very similar. An insect that looks, moves and acts like a pest may in fact be a look-alike or doppelganger. 

Doppelgangers may be related (e.g. same genus) or may not be related, as in the case of monarch butterflies (Danaus plexippus) and viceroys (Limenitis achrippus). Doppelgangers are  usually relatively harmless but sometimes the doppelganger is a pest yet their behaviour, lifecycle or hosts may be different. 

Correctly identifying a pest enables selection of the most accurate scouting or monitoring protocol. Identification and monitoring enables the application of economic thresholds. It also enables a producer to select and apply the most effective control option(s) including method and timing of application.  For the rest of the growing season, the Insect of the Week will feature insect crop pests and their doppelgangers.

Is that a midge or a parasitoid? Why does it matter?

Small insects (i.e., less than 5 mm) are difficult to identify, even for trained specialists and professional entomologists. Especially if they are alive, flying around. Or in a sweep net sample quickly assessed in the field. In the case of midge and small-bodied parasitoids, they can be easily mistaken for one another, but their roles in agriculture tend to be very different. 

Some of the most well-known prairie midge species are agricultural pests, such as the orange coloured wheat midge (Sitodiplosis mosellana), black-coloured Hessian fly (Mayetiola destructor), and alfalfa blotch leafminer (Agromyza frontella). Other midge species found on the prairies include biting midge like no-see-ums (Ceratopogonidae), black flies (Simuliidae), and non-biting midge (Chironomidae). Midge that are not considered agricultural pests may provide some ecosystem services (i.e., pollination), while other midge are disease vectors and are pests of medical and veterinary concern. 

A – Hessian fly – adult
Scott Bauer, USDA Agricultural Research Service, Bugwood.org
B – Swede midge – adult
Susan Ellis, USDA APHIS PPQ, Bugwood.org
C – Wheat midge – adult
Mike Dolinski, MikeDolinski@hotmail.com

Parasitoids are natural enemies of other insects. Thus, many parasitoids are important because they help control agricultural pest populations. Adult parasitoids lay eggs, usually singly, onto or into their host. The larvae that hatch from the eggs develop using the host as food, and eventually kill the host. An individual host usually provides enough food for just one parasitoid larva. For this reason, parasitoids species are rarely larger in size than their host species. On the prairies, important parasitoid families that may be mistaken for midge or other small, black insects include: Aphidiinae, Braconidae, Chalchididae, Encyrtidae, Eulophidae, Platygasteridae, Pteromalidae and Trichogrammididae. Sticky cards or sweep net samples may contain hundreds or thousands of small, black, winged insects. Many are probably parasitoids and not pests so look closely when scouting. A few key differences to watch out for include:

  • Parasitoids have two pairs of wings while midge have only one pair of wings     
  • Parasitoids are often shiny or metallic shades of black, blue, purple or green     
  • Midge may look hairy; parasitoids rarely look hairy.  
1 – Aphidiinae – adult (Aphidius avenaphis)
Tyler Wist, AAFC
2 – Braconid wasp – adult
Alberta Agriculture and Rural Development
3 – Chalcid wasp – adult (Phasgonophora sulcata)
Michael Gates, Encyclopedia of Live, EOL.org
4 – Tetrastichus julis – adult parasitizing a cereal leaf beetle larva
Swaroop Kher, University of Alberta/AAFC
5 – Ichneumonid – adult (Banchus flavescens)
John Gavloski, Manitoba Agriculture, Food and Rural Development
6 – Platygasterid – adult (Inostemma sp.)
Tyler Wist, AAFC
7 – Pteromalid – adult (Pteromalus puparum)
Koorosh McCormack, Natural History Museum: Hymenoptera Section, EOL.org
8 – Trichogrammid – adult (Trichogramma sp.) parasitizing an egg  
Jack Kelly Clark, University of California Statewide IPM Program

Specific information on these families of parasitoids and on the species of midge listed here can be found in updated Field Crop and Forage Pests and their Natural enemies in Western Canada field guide.

Review previously featured insects by visiting the Insect of the Week page.

Post contributed by Dr. Meghan Vankosky.

Insect of the Week – Doppelgangers: Bertha armyworm and clover cutworm

The case of the bertha armyworm and the clover cutworm (and other cutworm species)

Clover cutworm larva
cc-by 3.0 Lo Troisfontaine
Bertha armyworm – caterpillar 
Mike Dolinski, MikeDolinski@hotmail.com

Are those bertha armyworms (Mamestra configurata) eating your canola, mustard or alfalfa (also found on lamb’s-quarters, peas, flax, potato)? Or is it maybe a clover cutworm (Discestra trifolii)? [Note: not all cutworm species spend their larval stage underground.] The larvae of the two species are doppelgangers as they are similar in appearance, have a large overlap in host crops, and have similar timing (June-September). Telling them apart can be a challenge but here are few tips to focus on to help distinguish:

Colour:

  • there are generally fewer velvety black clover cutworm caterpillars, with most of the clover cutworm larvae being green or pale brown

Lateral stripe:

  • On the clover cutworm it is yellowish-pink
  • On the bertha armyworm it is yellowish-orange
Climbing cutworm larva – from Cutworm Field Guide
Climbing cutworm adults – from Cutworm Field Guide

In terms of scouting, economic thresholds and control options, treat both species as you would bertha armyworms.

Bertha armyworm – adult
Alberta Agriculture and Rural Development
Clover cutworm adult
cc-by-nc-sa 2.0 Ilona Loser

To learn more about bertha armyworms and clover cutworms, go to the Insect of the Week page or download copies of the Field Crop and Forage Pests andtheir Natural Enemies in Western Canada and Cutworm Pests of Crops onthe Canadian Prairies identification field guides.

Insect of the Week – Doppelgangers: Pea leaf weevil and other Sitona species

The case of the innocuous versus the evil twin: When making pest management decisions, be sure that the suspect is a actually a pest. This can be challenge since insects often mimic each other or look very similar. An insect that looks, moves and acts like a pest may in fact be a look-alike or doppelganger. 

Doppelgangers may be related (e.g. same genus) or may not be related, as in the case monarch butterflies (Danaus plexippus) and viceroys (Limenitis achrippus).  In some cases, doppelgangers are relatively harmless. In others, the doppelganger is a pest too yet behaviour, lifecycle and hosts may be different. 

Correctly identifying a pest enables selection of the most accurate scouting or monitoring protocol. Identification and monitoring enables the application of economic thresholds. It also enables a producer to select and apply the most effective control option(s) including method and timing of application.  For the rest of the growing season, the Insect of the Week will feature insect crop pests and their doppelgangers.

The case of the pea weevil and other Sitona species doppelgangers

Weevils of the genus Sitona are broad-nosed weevils that are pests of various legume crops, including field pea, faba bean, alfalfa and sweet clover. Sitona larvae attack the roots of the host plant and usually consume the root nodules and the enclosed symbiotic bacteria that fix nitrogen. Adult Sitona weevils consume plant leaves resulting in ‘U’-shaped feeding notches. Sitona species  known to occur in Canada include:

• Sitona lineatus –  pea leaf weevil (Fig. 1), has two primary hosts: field pea and faba bean.
• Sitona cylindricollis – clover root weevil or sweet clover weevil (Fig. 4).
Sitona hispidulus – clover root curculio* (Fig. 3), a clover pest.
Sitona lineellus –  alfalfa curculio (Fig. 5), eats alfalfa, vetch and field pea.
Sitona obsoletus (=S. flavescens = S. lepidus) – clover root curculio*, a clover pest (Fig. 6).

Note that common names can be used to describe more than one species and can be confusing.

Figure 1. Pea leaf weevil (Sitona lineatus L.).
Photo: AAFC-Sasktoon-Williams.

The above five Sitona species found in Canada are doppelgangers of each other for several reasons:

1. Similar in size and appearance – Require a taxonomic key and microscope to accurately identify to species. Notable difference is Sitona hispidulus which has hairy elytra compared to the other four species which lack hair on their elytra (Fig. 2). 

2.  Sitona weevils share primary and secondary hosts – Pea leaf weevils must feed on primary hosts (i.e., field pea and faba bean) to attain sexual maturation AND the larvae must feed on primary hosts to successfully develop. However, early in the spring and again in the fall, pea leaf weevils feed on virtually any species of legume, including the primary host plants of the other four Sitona species.

3. Foliar feeding damage is similar – According to Weich and Clements (1992), “careful scrutiny” is required to differentiate the feeding damage caused by different Sitona species feeding on the same host plant. Therefore, it is important to collect adult weevils for identification to confirm which species is responsible for foliar damage.

Figure 2. Characteristics of four of the five Sitona species found in Canada, useful when scouting for pea leaf weevils. See  also the pea leaf weevil monitoring protocol. Images © AAFC-Beaverlodge

Species pages for all five species available by searching the species names in the E.H. Strickland Entomology Museum: http://www.entomology.museums.ualberta.ca/searching.php

Figure 3. Clover root curculio (Sitona hispicula Fabricious).
Photo: © Donald Hobern  
Figure 5.  Alfalfa curculio (Sitona lineellus Bonsdorff). 
Photo: © by nc Chris Moody.
Figure 4.  Sweet clover weevil (Sitona cylindricollis Fahreaus). Photo: © Janet Graham.
Figure 6.  Clover root curculio (Sitona obsoletus).
Photo: by K. Walker

More information about pea leaf weevil (Sitona lineatus), and sweetclover weevil (Sitona cylindricollis) can be accessed on the Insect of the Week page. Information related to crop pests and their natural enemies can be found in the newly updated Field Guide and Cutworm Guide. Both are available for free download on our Insect Field Guide and Cutworm Field Guide pages.

Meghan Vankosky (@DrVanbugsky)