Alfalfa Snout Beetle

Agdex#:	121/622
Publication Date:	01/94
Order#:	94-025
Last Reviewed:	01/97
History:
Written by:	G. Peng - OMAFRA

Table of Contents

1. Introduction
2. Damage
3. Biology
4. Detection of Infestation
5. Control Measures

Introduction

The alfalfa snout beetle (ASB) is an introduced insect in North America. The insect was detected initially in New York state and has been a pest of concern there since 1933. The ASB has spread mainly in a northeasterly direction during last 60 years in New York state. Two localized infestations 50 miles apart exist in Ontario. One is on Wolfe Island where the initial find was made in 1967. The second infestation is on the mainland near Prescott and Brockville in Grenville and Leeds counties, an area consisting of about 14 km². Serious damage has been found on several farms in the area.

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Damage

Alfalfa snout beetle is the only insect pest that can completely destroy alfalfa stands within one or two years. The adult beetle feeds on leaves and stems of alfalfa, causing only marginal damage.

Figure 1. Adult of alfalfa snout beetle.

The grub (larva), feeds on the roots, often resulting in death of the plants in fall. The grubs cut off the side roots, girdle the main taproots, and may finally cut them off.

Figure 2. Larva of alfalfa snout beetle.

Figure 3. Aboveground symptoms of alfalfa in late summer due to the damage by snout beetle.

Sometimes they feed on the surface of the taproot, leaving a deep spiral groove or bore up through the heart of the root, leaving a shell of cortex intact.

Figure 4. Damage of alfalfa taproot by snout beetle.

Severely injured plants may appear yellow and often leafless in fall. When an extensive infestation occurs, dead areas may be seen throughout a field.

Figure 5. Dead area in alfalfa field caused by snout beetle.

Impact of ASB on a dairy farm has conservatively been estimated at a 20-30% increase in feed costs due to the increased cost of alfalfa production, poor quality forage and "off-farm" purchases of high quality hay.

Alfalfa snout beetle has a wide range of hosts. Although it finds alfalfa to be the most attractive crop, larvae of the insect may attack all species of clover, grape and strawberry. They sometimes even feed on weeds, especially the ones with fleshy roots such as wild carrot and dandelion.

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Biology

The snout beetle has a two year life cycle, most of which is underground. This behaviour makes detection difficult, and damage to the crop may develop without the grower knowing the real cause.

All the adults are female, and a single beetle accidentally introduced into a non-infested area is capable of starting a new infestation. The adults are flightless. Migration by walking normally enable them to move only several hundred metres per year, but may increase their exposure to other means of travel such as waterways. Long distance travel of the adult can also occur through the shipment of pit gravel and freshly baled hay, the movement of farm machinery and even the relocation of beehives.

The snout beetle overwinters as an adult beetle in a pupal cell. Adults emerge early in spring, normally during mid- to late April. They feed on new shoots growing from alfalfa crowns, and migrate to lay their eggs. The migration can be observed along road sites and fence rows when the beetles are abundant.

Eggs are laid singly around crown of alfalfa in the upper 5 cm of soil. In wet weather, eggs may be deposited on the soil surface. On average, each beetle lays over 300 eggs. The eggs may hatch in about two weeks into tiny, legless grubs which first feed on crowns, and soon start feeding on the side and taproots of alfalfa plants.

Late in the summer the larvae are nearly full-grown (about 2 in.) and burrow deep into the soil where they spend the winter. During the following spring these grubs move closer to the soil surface and continue to feed until midsummer, then they pupate and become inactive adults which remain in the soil until the following spring.

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Detection of Infestation

New infestations may be detected by walking in alfalfa fields in early spring and late summer. During mid-April and early May, growers in Southern Grenville and Leeds counties should check their alfalfa fields and roads near the fields to spot migration of adult beetles and dead areas of alfalfa.

The dead areas are easily seen in early spring but are quickly filled in later by grass and weeds. During dry years, severely injured plants often yellow during late August, die and turn brown by mid-September. By fall, dead areas may be common throughout heavily infested fields.

Suspicious plants should be dug and examined for damage and presence of the grubs. In normal or wet years, yellow plants may not be common in early fall. However, alfalfa plants severely damaged by ASB are frequently heaved out of the ground during winter and spring.

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Control Measures

The first line of defence is to avoid spread of the insect to non-infested areas. The following guidelines may help to reduce the risk:

1. Farm equipment should be cleaned thoroughly before being moved out of an infested field.

2. Pit gravel should not be transported out of the infested area during the period of adult beetle activity, i.e. roughly from early April to early June.

3. Beehives should not be transported out during this period either.

4. First cut hay from infested fields should be stored at least two months before being shipped out. Second and third cut hay is not a risk.

Rotation of alfalfa with non-host crops breaks the cycle and decreases the population of snout beetle significantly. Non-host crops include com, small grain cereals, and soybeans. In heavily infested fields, it is recommended that the rotation crops are grown for at least two years to reduce the insect population dramatically.

Fields which are heavily infested by ASB and plowed under should never be seeded to alfalfa. Such action may result in the loss of an entire new seeding. Plowing an infested field next to a new alfalfa seeding in spring may pose an unnecessary risk, since most adults may migrate to the new field.

There is no effective natural parasites of ASB known in Ontario. In research, larvae of ASB were found being parasitized by a species of nematode. Application of the nematode to infested fields suppressed the insect and reduced damage. However, no biocontrol product is commercially available yet.

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