Pea Weevil

Appearance

Adult beetles of "S. lineatus" measure 3.4-5.3 mm in length. They are characterized by a series of colored scales arranged in alternating lines on the elytra; it is from this characteristic where the species gets its name lineatus meaning 'lined' or 'striped'. The head and pronotum also have fine pointed setae amongst the scales. The antennae are clubbed, pointed and preceded by 7 segments. The femora is dark, but tibiae and tarsi are red. As a member of Order Coleoptera their forewings are modified to form hardened covers over the thorax and abdomen, with the hindwings for flight underneath.

Distribution

"S. lineatus" is native to Europe and North Africa, and is considered an invasive species in North America. They are typically found in the western prairie provinces of Canada and are expanding east from Saskatchewan, south near the Canada/USA border into North Dakota, and north into higher latitudes of Alberta. Expansion is limited by both temperature and precipitation, but they are more sensitive to precipitation. Climate models have predicted the potential for expansion north in those distribution territories.

Behavior

"S. lineatus" are univoltine species that are oligophagous within the Fabaceae plants. Adults will overwinter in the field margins of pea, bean crops, or migrate to fields of alfalfa before the onset of winter. Their emergence from winter dormancy is related to temperature, as adults have been seen to prefer temperatures of 12.5 °C as an indicator to leave their winter site habitat, with wind currents being the main mechanism by which they find and colonize new crop habitats. Both males and females have been shown to have increased longevity when feeding on pea plants as opposed to the alfalfa they eat over winter and in spring prior to migration. Increased longevity for females translates to higher fecundity, and females will disperse from areas of high population density to areas with low density to maximize their egg to plant ratio. Females that feed on pea crops generally have a higher reproductive capability than ones that feed more on alfalfa, it is advantageous to migrate from the field margins and winter shelters to the new pea plants emerging in spring. After the respective reproductive periods in spring for males and females, adults will feed on the leaves of Fabaceae plants, and larvae will burrow into the soil after hatching where they feed primarily on "Rhizobium" at the nodules of the root system. During their feeding underground, larvae go through 5 stages of growth, and emerge as adults to feed on the crop above ground just as their parents in mid summer. In late summer the surviving adults leave the crop plants and migrate to the field margins, alfalfa fields, or other areas of habitat that make suitable shelter for the overwintering period of dormancy.

Cultural

The impact of this invasive species can be difficult to estimate accurately as its distribution is widespread, and there are often abiotic factors that determine the success of "S. lineatus" which are inconsistent within its indigenous and invasive habitat ranges. There is a way to focus on these types of pests and how to look at them in terms of potential cropland for their habitation. In 2018 in Canada, for example, approximately 3.6 million acres of pulse crops were grown, valuable domestically and as an export, the yields can be diminished as much as 28% from feeding activities of "S. lineatus". Damage to pea and bean crops can be severely impacted by "S. lineatus" feeding, due to the fact that both the root "Rhizobium" and foliage are fed upon by larvae and adults respectively. These crops are important as food resources and as nitrogen fixing plants, an ability which is reduced when larval feeding on rhizobium is significant enough. The damage to root nodules from hosting larvae can lead to decrease pod production, lower protein content of peas or beans, and the necessity of artificially fertilizing pulse crops and the increased cost associated with this,