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Sitona weevil
The main species attacking lentil is Sitona crinitus Herbst (Sitona macularius Marsh.) (Coleoptera: Curculionidae). It has been reported from southern Europe, North Africa, West Asia and the former USSR. In several countries of West Asia (Turkey, Syria, Lebanon, Jordan) it is the main insect pest of lentil. Other Sitona species found feeding on lentil are Sitona lineatus L. and Sitona limosus Rossi.
The adult weevils have a grey-brown, elongated body 3-4 mm long. The pronotum has three straight longitudinal light lines and the elytra has three rows of dark and white spots (Fig. 49). The females lay spherical yellow eggs which later turn black. The larvae are cream white, with a brown head capsule, and legless. The pupae also are white (Fig. 50).
In the Mediterranean region, where hot and dry summers prevail, the adults aestivate in the soil and start emerging in December/January. After copulation the females start laying eggs on the soil around the lentil plants or loosely on the leaves; the latter fall to the ground. The oviposition period lasts for several months and each female lays several hundred eggs. The hatching larvae move into the soil and infest the nodules. Each larva may consume many nodules during development until pupation occurs in the soil. Depending upon temperatures, the larval and pupal period may last 5-6 and 3-4 weeks, respectively. The neonate adults emerge in May at the time of lentil maturity. These adults might feed little on other crops, but then enter the soil to aestivate until early winter. The adults of the previous generation will die in April/May. Thus there is only one generation per year and the adults live for almost one year.
Type of injury: Early in the season the adult weevils feed on the foliage in a characteristic manner, eating out semicircular notches from the leaf edges (Fig. 51). The adult feeding usually does not affect yields, unless populations are very high and/or unfavorable environmental conditions limit the growth of the lentil seedlings and they cannot quickly compensate the damage by regrowth of foliage.
The main damage is caused by the larvae, which infest the root nodules. The white Sitona larvae inside the nodules or empty nodules can be found in uprooted lentil plants (Fig. 52). This reduces the nitrogen-fixing ability of the crop. In severe attacks the foliage can assume the yellow appearance characteristic of nitrogen deficiency (Fig. 53).
Control: Apply granular insecticides (e.g., Carbofuran 5% G at 10 kg/ha) at planting.
Treat seed with PrometR (Furathiocarb) at 12 ml/kg seed.
If no preventive control was taken and a high infestation level is observed in the field, use an insecticide spray (e.g., ImidanR (Phosmet) 1 kg a.i./ha. This is less effective than granular application and seed treatment.
Crop rotation can reduce the infestation to some extent, as the weevils emerge from the soil after aestivation. They are, however, strong fliers and can migrate long distances.
Cutworms
Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae) is a cosmopolitan, polyphageous insect. Other Agrotis spp. are of localized importance.
The adult moths are grey-brown and fairly large (35-50 mm wingspan). The forewings are light brown and patterned, the hind wings are pearly white with brown margins (Fig. 54).
The young larvae are green or greyish, later becoming dark green or grey, and marked with two bright lines. The mature larvae are cylindrical and 45 cm long. Both adults and larvae are nocturnal. Larvae, typically coiled up (Fig. 55), can be found in the soil around damaged plants.
Eggs are laid on the soil or on the underside of leaves of weeds and crops. Mature larvae bury deeply into the ground and pupate within cells, from which the adults emerge. Depending on the climate there might be one or several generations per year.
Type of injury: The larvae cut the plant at or slightly above the root crown and sometimes drag it to their burrows in the soil. Most of the plant is not consumed; after cutting one, larvae move to another, leaving the plants to wither and dry.
Some species feed on the upper leaves before moving to the soil surface.
Control: The abundance of A. ipsilon in some areas is partly affected by rainfall. In the drier areas (e.g., Syria) infestations are higher in years with high rainfall. The best way to control cutworms is to broadcast a poison bait prepared with wheat bran, cotton, or groundnut cake, moistened with water and trichlofon (Dipterex), carbaryl (Sevin) and Parathion. The poisoned bran is then broadcast over the field (10 kg/ha), preferably in the evening.
Weed control helps to prevent infestations because cutworms prefer weedy fields for oviposition.
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