|scientific name Sitona lineatus |
common name Pea Leaf Weevil
Pisum sativum (field pea) and Vicia faba (faba beans) agricultural production systems (Jackson 1920).
Adults migrate in spring to host plants and in autumn before overwintering (Fisher and O’Keeffe 1979a).
Body length ranges from 3.2 to 4.5 mm. Integument is generally black or light brown, with variations. Antennae, tibia and tarsi may be reddish, these also vary. Rostrum is flat, but lower third is bisulcate with indistinct median carnia located between apical concavities. Rostral surface is shiny, with deep and close punctures, each puncture possesses a slightly erect and narrow scale. Recumbent scales are located in the interpucture spaces. Eyes are moderately convex. Pronotum is widest slightly behind the mid-line, sides are arcuate, anterior constriction line is only weakly evident. Surface of pronotum is shiny, with many close and deeply impressed punctures, with scales as on the rostrum. The prosternal groove touches the fore-coxae cavities. Vestiture of elytra with intermixed elongate and small scales and recumbent to slightly erect flattened setae that are as long as or slightly longer than the scales. Setae and scales occur in approximately equal numbers. Stripe pattern is variable, with white scales often on striae 3, 5, and 7, and brown scales on 2, 4, and 6. (Adapted from Bright 1994, Bright and Bouchard 2008)
Adults of Sitona lineatus are distinguished from their close relatives by the elytra stripe pattern that extends onto the pronotum. When weevils have lost the scales that form the stripe pattern, due to age or activity, they can be easily distinguished by examining the ventral surface of the pronotum. The fore-coxal cavities touch, or nearly touch, a narrow groove located on the ventral surface of the pronotum. In all other Sitona species, the fore-coxae do not touch this groove. (Adapted from Bright 1994, Bright and Bouchard 2008)
Adults overwinter in shelterbelts and fields where perennial legumes (secondary hosts) are found (Jackson 1920, Murray and Clements 1992). Secondary hosts may be consumed during the overwintering period when temperatures are mild (Murray and Clements 1992). Spring migration begins after temperatures reach a 12° C threshold, and is achieved via flight (Fisher and O’Keeffe 1979a, Hamon et al.1987). Mating and oviposition begin after primary hosts are located in spring and continues until mid-August, when the overwintered generation begins to die out (Jackson 1920). One adult female may lay between 500 and 3000 eggs, which are scattered upon the soil surface as she feeds (Jackson 1920). Eggs are white when first deposited, and melanize within 24 hours (Schotzko and O’Keeffe 1986). The incubation period is dependent upon moisture and temperature levels (Lerin 2004). Larvae occupy root nodules of the primary host, where they consume Rhizobium leguminosarum bacteria that fix nitrogen (Jackson 1920, Johnson and O’Keeffe 1981). Inside the nodules, larvae are also protected from disease and predation. Pupation occurs in the soil. New generation adults begin emerging in mid-July and feed until temperatures drop (Jackson 1920; Hoebeke and Wheeler 1985).
The pea leaf weevil is a pest in all regions where it occurs.
Larvae are restricted to feeding on the root nodules of two primary host plants: Pisum sativum (field pea) and Vicia faba (faba bean), where they consume the nitrogen-fixing Rhizobium leguminosarum biovar viciae bacteria in root nodules (Jackson 1920, Landon et al. 1995). Secondary hosts of adults include most other legume species, with possible exceptions including the common bean and lentils (Fisher and O’Keeffe 1979b & 1979c, Schotzko and O’Keeffe 1988).
This species occurs throughout Europe, including the United Kingdom, Poland and Germany and northern Africa (Jackson 1920, Hans 1959). In North America, it is found in southern British Columbia, the northwestern United States including Washington, Oregon, California, Idaho (Downes 1938, Bright and Bouchard 2008), and Florida (Bloem et al. 2002). It also occurs in southern Alberta, where it has been found as far north as Olds, and Saskatchewan (Coles et al. 2008).
Distinctive "U" shaped notches are made along the leaf margins of host plants of feeding pea leaf weevils (Jackson 1920). The intensity of leaf-notching can be used to indirectly estimate the population density and severity of an outbreak (Cantot 1986). Economic thresholds employed in the United States and Europe for the control of this pest include an average of ten eggs per plant or three weevils per sweep (Doré and Meynard 1995, Quisenberry et al. 2000). However, when startled or approached, weevils tend to fall to the soil and 'play dead'. This habit limits the accuracy of sweep sampling. Control of the pea leaf weevil has been well studied in Europe and the US. A male produced aggregation pheromone, 4-methyl-3, 5-heptanedione has been identified for the pea leaf weevil, that may play a role in controlling this pest (Blight et al. 1984, Blight and Wadhams 1987).
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