G. W. Barber.
The Efficiency of Birds in Destroying Over-Wintering Larvae of the European Corn Borer in New England.
Psyche 32(1):30-46, 1925.

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30 Psyche . [February
THE EFFICIENCY OF BIRDS IN DESTROYING OVER- WINTERING LARVB OF THE EUROPEAN CORN
BORER IN NEW ENGLAND.!
Cereal and Forage Crop Insect Investigations, Bureau of En- tomology, U. S. Dept. of Agriculture.
Several years ago, not long after investigations of the European corn borer (Pyrausta nubilalis Hiibn.) were begun by the Bureau of Entomology of the United States Department of Agriculture, it was frequently observed that cornstalks infested by the larvae of this insect showed in the spring of the year numerous holes along the stalks, the burrows of the insect beneath these holes being empty. This was the first evidence of any appreciable feeding by birds on this insect. Such evidence of bird feeding has been found each spring and it is now possible to associate this work with the downy woodpecker (Dryobates pubescens medianus Swainson) a winter resident in this region. In numerous instances, this bird has been observed at close range at work on the infested standing cornstalks. Plate IA, shows sections of cornstalks from which the larvae of the corn borer have been removed by this bird. This type of feeding by chickadees (Penthestes atricapillus atricapillus Linn.) has also been observed by Mr. F. H. Mosher.
Within the last few years observations have shown another type of feeding by birds on the overwintering larvae of this insect. This is the shredding of cornstalks illustrated in Figure lB, and is the result of feeding by grackles, blackbirds, starlings and probably several other species of migrating birds. These birds arrive in the latitude of Boston, Mass., from the middle to the last of April. Such work was especially noticeable in corn- stalks that had been piled in the fall or in stalks that had fallen over for one reason or another and lay on the surface of the soil. These birds have frequently been observed feeding in flocks in the spring, and in a short time .they are able to gather the larvae Contribution from the Bureau of Entomology, U. S. Department of Agriculture in cooperation with the Entomological Laboratory of the Bussey Institution, Hanard University, Bussey Institution No. 248. Pu&e 3k30.47 (1925). hup Ytpsychu einclub orgt12/32-030 html



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19251
Efficiency of Birds in Destroying Larvce of Corn Borer 31
from quite a number of cornstalks. They are able also to shred infested corn stubble and take the larvae in the more exposed positions, but apparently are not able to reach the larvae con- t,ained in standing stalks.
In the fall of 1922, when it was apparent that the birds were becoming a really important factor in the reduction of the num- bers of the corn borer, experiments were undertaken to determine how extensive such feeding was. These experiments were also carried on during the winter of 1923-1924. The object of this work was to obtain information on the extent of the combined feeding by all species of birds concerned rather than the extent of feeding of any particular species, the intention being to obtain as far as possible a picture of the present importance of birds as a group in relation to this insect rather than a study of the value of any one particular species.
The studies pursued during the fall of 1922 and the spring of 1923 may be treated under two heads; first, the extent of bird feeding on the larvae in infested cornstalks placed in the field for this purpose; second, the extent of feeding by birds on larvae in host plants that remained undisturbed in natural positions during the winter.
In the first part of this work twenty representative locations were selected throughout the infested area of eastern New Eng- land. In each of these locations ten stakes were set upright in the soil, there being six infested stalks fastened to each of these stakes. The three following types of corn were represented at each location: pop corn, sweet corn (Golden Bantam) and field corn (Longfellow Flint). Counts of the larval population of representative stalks during the fall gave an average figure as to the number of larvae expected from each stalk, and from this average the number of larvae expected from each station was computed. This series of experiments was placed in the field in November, 1922, after all larval activity had ceased, and the stalks were collected in April, 1923, before larval activity had commenced in the spring. The chance of losing an appreciable number of larvae by migration 'was small, since during this period the larvae were entirely dormant and inactive. Of these twenty experiments five showed extensive feeding by birds



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32 Psyche [February
when examined in the spring, mostly the work of woodpeckers. Of the remaining fifteen experiments one was destroyed by an over-anxious farmer, one was partly destroyed by a tractor and the others showed only very slight traces of feeding by birds or no evidence of bird feeding whatever. Table Number 1 shows the extent of bird feeding on the five experiments at,tacked, and the recovery of larvae from stations that escaped noticeable bird feeding. The average recovery of larvae from experiments not attacked by birds was 1,090 larvse per station as compared with the average expectancy of 1,223.2. This apparent loss of 10.8 per cent of expected larvae per station was undoubtedly TABLE I
Extent of Feeding by Birds on Experimental Material in the Spring of 1923. Experiments on which birds fed.
Location
-
Scituate, Mass.
Newbury, Mass,
Rockport, Mass,
Medford, Mass
Arlington, Mass
Experiments on which birds did not feed. iV-20
IV-29
IV-28
IV-10
IV-7
IV- 1 1
i V-6
IV-14
!V-6
1V-14
V-8
IV-7
IV-I I
Bristol, N. H.
Framington,N.H.
Wells, Me.
Concord, Mass.
Falmouth, Mass.
Quincy, Mass.,
Harwich, Mass.
Methuen, Mass.
Manomet, Mass.
Tyngsboro, Mass.
Wareham, Mass.
Wellfleet, Mass.
Worcester, Mass.,
Xl-8
XI-7
XI-7
XI-4
X-31
XI-4
XI-I
XI-2
X-30
X 1-8
XI-I
X-31
X-26




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192.51
Efficiency of Birds in Destroying Larvae of Corn Borer 33
caused by migration of a few larvae and the loss of small pieces of stalks containing larvae during transportation of the corn- stalks used in the experiment.
The average winter mortality in the 18 experiments listed in table No. 1 was 10.5% per cent. The average per cent of larvae credited to bird feeding in the five stations where stalks were attacked, was 61. The average per cent of larvae credited to bird feeding in the 18 stations recovered was 17. The stations that showed extensive feeding by birds (Fig. 1) are all within the area most heavily infested by the European corn borer and localities where infestation has been severe for several years. Because of this fact and because no marked evidence of bird feeding was found in areas slightly infested or areas that had become heavily infested by the insect within the last year or two, it would appear that woodpeckers are aware of the fact that infested cornstalks contain desirable food only in this heavily infested area, and that in more sparsely infested regions or in areas where infestation had but recently become severe they are for the most part still unfamiliar with the exis- tence of this source of food.
Several of the more commonly infested weeds and cul- tivated plants were also tied to stakes to observe possible feeding by birds on larvae contained in such plants. These were placed with the experiment at Medford, Mass., mentioned in Table 1, where birds took 69 per cent of the larvae from the cornstalks tied to stakes.
Of the several plants thus observed, common sunflower (Helianthus annuus L.), Princesplume (Pol'ygonum orientate L.), Polygonum sp., and cocklebur (Xanthium spp.) showed extensive feeding by birds of the same sort attributed to woodpeckers while no evidence of such feeding was noticed in Abutilon (Abutilon theophrasti Medic,), pigweed (Amaranthus retroflexus L.), rag- weed (Ambrosia sp.,) beggar-ticks (Bidens sp.), pot-marigold (Calendula officinalis L.), aster (Callistephus sp.), feather cocks- comb (Celosia argentea L.), Cosmos bipinnatus Cav., Dahlia sp., barnyard grass (Echinochloa crusgalli L.), Japanese millet (Echi- nochloa sp.) , Gladiolus sp., strawflower (Helichrysum bracteatum



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34 Psyche [February
Andr.), geranium (Pelargonium hortorum), lirna bean (Phaseolus lunatus, L.), and African marigold (Tagetes erecta L.) . The field examinations of cornstalks showed much the same evidence as was obtained from the experimental work described in the preceding paragraphs. Numerous instances were found where birds had removed a high percentage of the larval content of cornstalks and such instances were found only in heavily Fig. 1.
Map of the area known to be infested by the European Corn Borer in New England in 1922.
Circles show localities where experiments were placed in the fall of 1922 ; clear circles indicate that no feeding by birds was found, while circles having a cross in the center indicate localities where birds fed on larvae contained in the corn stalks of the experiment. A white line surrounds the area known to be infested up to July 1, 1919. 1-Arlington, Mass. 8-Tyngsboro, Mass. 14-Quincy, Mass. 2-Medford, Mass. 9-Bristol, N. H. 1 5-Scituate, Mass. 3-Rockport, Mass. 10-Concord, Mass. 16-Wareham, Mass. 4-Newbury, Mass. 11-Worcester, Mass. 17-Falmouth, Mass. 5-Wells, Me. 12-Walpole, Mass. 18-Manomet, Mass. 6-Methuen, Mass. 13-Taunton, Mass. 19-Harwich, Mass. 7-Farmington, N. H.




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19251
Efficiency of Birds in Destroying Larvce of Corn Booer 35
infested areas and in localities that had been infested for several years. In sparsely infested localities or in areas where infesta- tion had been severe only recently, no extensive feeding was noticed although in some cases there were traces of feeding by birds. The following table shows the condition as found in certain heavily infested fields that were found to be attacked by birds.
TABLE 11.
Extent of Feeding by Birds on Material Undisturbed by Man in the Spring of 1923.
Locality
Watertown, Mass,
Milton, Mass.
Marblehead,
Mass.
Melrose, Mass.
Date
examinee
--
IV-2-23
IV-6-23
Iv-13-23
v-3-23
v-11-23
Type
Estimatec
number
of larvee
taken by
birds
I 86,480
26,957
.........
140,946
.........
Estimated
per cent
of larvae
taken by
birds
--
92 %
78%
30%
97%
80%
Condition
I 3 acre;
1 acre
I acre
acre
.......
=Standing
and broken
over
' standing and
--
The figures mentioned in this table were obtained by counting the number of cornstalks in the several fields, estimat- ing the fall infestation of the stalks, and comparing this figure with the average infestation found on the date of the examina- tion. The spring infestation per cornstalk was obtained by averaging several series of counts made in different parts of each field. In all these instances both types of bird feeding shown in figure 1 were found, the feeding attributed to woodpeckers being extensive in standing stalks and the stalks lying on the ground being shredded by other birds.
In weeds instances were found of the removal of considerable numbers of larvae from cocklebur (Xanthium sp.) and barnyard grass (Echinochloa crusgalli L.). In one field several score of Size
cz:n of corn-
stalks
"
"
of are;
broken over
Lying on
soil
standing and
broken over
' In piles
partly burn-
1 ed




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36 Psyche [February
dahlia plants were found from which birds had removed nearly all the larvae of the European corn borer that these plants had harbored.
Although birds (particularly the downy woodpecker) feed to a limited extent on the larvae of this insect in the fall and winter, most of the feeding is done in the spring, especially the shredding of stalks lying on the ground. The experiment placed
in Medford, Mass.,
(table I), showed on April 9, 1923, that birds had by that time taken 65 per cent of the larvae from the cornstalks. A similar experiment in the same locality was continued until June 27, 1923, a date when most of the insects had transformed to adults. At that time examination showed that birds had apparently taken 82 per cent of the insects from - the cornstalks.
In the fall of 1923 a series of experiments much similar to those previously described was placed in the field for the purpose of obtaining information on the extent of feeding by birds on this insect. However, this time fifty stations were chosen instead of twenty as in the previous work. Each station was composed of four stakes to each of which was fastened five infested corn- stalks, the larval expectancy as obtained from stalk counts being on an average of 15.5 larvae per stalk.
These stations were so selected as to cover the entire area infested by this insect in New England and were run out in lines as straight as possible from Arlington, Mass., as a center as fol- lows: first line comprising 12 stations in a northeasterly direction as far as Sebago, Me.; second line comprising 5 stations in a northerly direction as far as Farmington, N. H.; third line com- prising 8 stmations in a direction north by northwest as far as Bristol, N. H.; fourth line to the northwest as far as Gardner, Mass. comprising 3 stations; fifth line comprising 4 stat'ions to the west as far as Worcester, Mass.; sixth line to the southeast as far as Touisset, Mass., composed of 4 stations; seventh line to the south as far as Mattapoisett, Mass., composed of 4 sta- tions; eighth line composed of 9 stations to the southeast and extending on Cape Cod as far as Provincetown, Mass. Fig. 2.




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19251
Efficiency of Birds in Destroying Larvce of Corn Borer 37
Fig. 2.
Map of the area known to be infested by the European Corn Borer in New England in 1923.
Circles show localities where experiments were placed in the fall of 1923;-clear circles indicate that no feeding by birds was found, while circles having a cross in the center indicate localities where birds fed on larvae contained in the corn stalks of the experiment. A white line surrounds the area known to be infested up to July 1, 1919. 1-Arlington, Mass.
2-Medford, Mass.
3-Saugus, Mass.
4-Beverly, Mass.
&-Marblehead, Mass.
6-Rockport, Mass.
7-Newbury, Mass.
8-Hampton, N. H.
9-Kittery, Me.
10-Wells, Me.
1 1-Biddeford, Me.
12-Scarboro, Me.
13-Woburn, Mass.
14-Andover, Mass.
1 5-Methuen, Mass.
16-Kingston, N. H.
17-Farn~ington, N. H.
18-Bedford, N. H.
19-Hillsboro, N. H.
20-Concord, N. H.
21ÌÔFranklin N. H.
22-Bristol, N. H.
23-Concord, Mass.
24-west ford, Mass.
25-Harvard, Mass.
26-Leominster, Mass.
2 7-Gardiner, Mass.
28-Natick, Mass.
29-Southboro, Mass.
30-Worcester, Mass.
31-Medfield, Mass.
32-Foxboro, Mass.
33-Attleboro, Mass.
.34-Touisset, Mass.
35-Needham, Mass.
36-Bridgewater, Mass.
37-Mattapoisett, Mass.
38-Milton, Mass.
39-W. Hingham, Mass.
40-Cohasset, Mass.
41-Marshfield, Mass.
42-Kingston, Mass.
43- Falmouth, Mass.
44-Sandwich, Mass.
45-Brewster, Mass.
46-well fleet, Mass.
47-Provincetown, Mass.




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38 Psyche [February
Examinations of the cornstalks of these experiments in the spring of 1924 showed that 16 of these stations exhibited feeding by birds to a noticeable extent, while the remainder showed either a mere trace of bird feeding or no evidence of such feeding at all. In Table 3 those stations that showed bird feeding are listed together with the number and percentage of larvae ap- parently removed from the stalks by birds. The average winter mortality for the 38 stations listed in table no. 3 was 4 per cent.
The average per cent of larvae apparently taken by birds in the 16 stations that showed bird feeding (based on the average recovery per stalk in experiments not touched by birds) was 54. The average per cent of larvae apparently taken by birds in the total number of 47 experiments (based on the average recovery per stalk in experiments not touched by birds) was 19. Three stations were lost or destroyed, leaving 31 that showed either a mere trace of bird feeding or none at all. The infestation in the fall was on an average 310 larvse per station. Spring ex- aminations of the 31 stations that showed no important feeding by birds proved that the average infestation at that time was 14.7 larvae per stalk or 294 larvae per station, an apparent loss per station of 16 larvae or approximately 5 per cent of the ex- pected larvae. This loss is slight when it is remembered that in some stations birds apparently did take a few of the larvae, and that the cornstalks were necessarily handled several times and were transported for considerable distances, so that small pieces were sometimes broken off and lost. These figures, however, are offered to show that the findings as regards bird feeding, shown in Table no. 3, present a fair picture of the extent to which birds fed on this material.
These results show a considerable increase in the area in which birds fed extensively, (Fig. 2 and 3) over the results ob- tained in the spring of 1923. This may be due to the fact that the larger number of stations provided a much more accurate test of conditions and so gave a much better picture, or it may indicate a widening field over which birds have become aware of an existing food supply. There is also a possibility of the element of chance entering to the extent that if the right species of birds



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19251
Efficiency of Birds in Destroying Larvce of Corn Borer 39
found the stations, feeding would result, whereas if the experi- ments remained undiscovered by birds able to take larvae from the cornstalks no evidence of feeding would be found. Whatever the reason, however, the fact of evidence of bird feeding on over- wintering larvae of this insect in cornstalks over a much more extended area during the spring of 1924 than was observed previously remains, and it is the writer's belief that birds were a more important factor in reducing the numbers of the European corn borer in the spring of 1923 than in a corresponding period in 1922, and that in the spring of 1924 they were of greater im- portance than in the same period in 1923; in other words, that the importance of birds as a means of natural control has been increasing each spring for the last three years. The figures showing the percentage of larvae taken by birds as shown in Table 3 represent the feeding up to the time that the experimental material was collected in the spring and so do not show the total amount of feeding that birds might have done had the material remained in the field a few weeks longer. As already mentioned, this same condition prevailed in the con- sideration of the experiments examined in the spring of 1923. It was necessary, however, to collect these experiments early in April because of a desire to examine the cornstalks before the larvae had moved from the exact locations in the stalks in which they rested at the time the material was set but the previous fall.
It is probable also that birds were unable to remove some of the larvae from the staked experiments because in tying corn- stalks to the stakes that part of the stalks lying next to the st'akes was rendered inaccessible to the birds. In the series of experiments examined in the spring of 1924, several of the experiments that showed no feeding by birds were located in areas that had been heavily infested by the insect for several years. Noticeable among those was the experiment located in Saugus, Mass. (table 3). This experiment was placed on a farm where corn had been severely infested each year since 1919. In this instance, however, little corn was grown in 1923 because of the heavy infestation previously experienced. A second instance of this condition was found in Marblehead,



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Psyche [February
TABLE NO. 3.
Extent of Feeding by Birds on Experimental Material in the Spring of 1924. Experiments on which birds fed.
Locality
-
Arlington,
Attleboro,
Beverly,
Brewster,
Cohasset ,
Falmouth,
Harvard,
Leominster,
Marshfield,
Medford,
Milton,
Newbury,
Rockport,
Southbcro,
Wellfleet,
Woburn,
Mass
Mass
Mass
Mass
Mass
Mass.
Mass
Mass
Mass
Mass
Mass
Mass.
Mass.
Mass.
Mass.
Mass.
Andover,
Bridgewater,
Concord,
Foxboro,
Gardner,
Hingham,
Kingston,
Marblehead,
Mattapoisett,
Medfield.
Methuen,
Natick,
Needham,
Provincetown.
Sandwich,
Saugus,
Touisset ,
Worcester,
Westford,
Biddeford,
Kittery,
Scarboro,
Wells,
Bedford,
Bristol,
Concord,
Farmington,
Franklin,
Hampton,
Hillsboro,
Kingston,
Experiments on which birds did not feed
Mass. 11-19
Mass. 11-27
Mass. 11-16
Mass. 11-28
Mass. 11-29
Mass. 11-20
Mass. 11-24
Mass. 11-15
Mass. 11-27
Mass. 11-24
Mass. 11-19
Mass. 11-23
Mass. 11-16
Mass. 11-24
Mass. 11-23
Mass. 11-14
Mass. 11-28
Mass. 11-27
Mass. 11-15
Me. 11-22
Me. 11-22
Me. 11-22
Me. 11-22
(partly destroyed)
(partly destroyed)
1Based on the average larval contents of stalks in the fall. 2Based on the average larval recovery at stations not attacked by birds.



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19251
Efficiency of Birds in Destroying Larvae, of Corn Borer 41
Mass., where birds did not feed on the larvae contained in the cornstalks of the experiment (table 3) although it was found in the spring of 1923 that they had removed a high per cent of the borers from a field of heavily infested cornstalks (table 2). From these instances it appears that birds might not be depended on to feed on corn borer larvae in cornstalks in the same locality each year.
On the other hand, heavily infested localities are known, noticeably Medford, Mass., where birds have fed on overwintering larvae consistently in the springs of 1922, 1923 and 1924.
Throughout the infested area of Massachusetts there was very little corn standing in the field during the winter of 1923- 1924.
The condition of all the experiments was the same, there- fore, in that practically no cornstalks other than the experiments were to be found by the birds and for this reason there was no influence brought to bear, as far as the extent of feeding was concerned, by proximity of the experiments to infested cornfields. Because of the general scarcity of standing corn during the winter of 1923-1924 it might appear that a condition of con- centrated feeding on the experimental material might result. It does not seem that any such phenomenon took place, however, because in the experiments examined in the spring of 1924, in no case was the bird feeding found to be as extensive as on the TABLE NO. 4.
The Extent of Bird Feeding on Experimental Material at Medford, Mass., on different dates in the Spring of 1924. Date
Examined
Apparent
number
taken
by birds
5 5
82
9 3
47
I 05
123
1.27
Number
of
stalks
Apparent
per cent
taken
by birds
----
35.5
53.
60.
30.3
67.7
79.3
88.4
10 I55 100
Number
of
expected
larvae
------
Number
of
larvae
recovered
--




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42 Psyche [~ebruar~
stalks of several cornfields examined in the spring of 1923 and listed in table 2.
When birds feed in the spring on larvae contained in corn- stalks that were piled up the previous fall and remained in such condition through the winter, an interesting phenomenon is frequently noticed. In the spring, larvae desert the wet corn- stalks in the lower parts of such a pile, migrating to the dry stalks above where conditions for transformation are much more favorable. It is on the larvae contained in these dry stalks on the top of the pile that birds such as grackles and blackbirds feed extensively so that as the spring advances it is frequently found that few larvae remain in the lower stalks of the pile because of the migration of the stalks above, and a few larvae re- main in the dry stocks on the top of the pile because birds have shredded the stalks and removed a high percentage of them. This condition has been found several times experimentally, and has been noticed in several localities in the fidd where cornstalks have passed the winter in piles.
Observations as to the extent of feeding by birds on larvae in cornstalks standing undisturbed in the field in the spring of 1924 were possible in only a few localities, mostly in very small lots of stalks because of a law in the state of Massachusetts compelling all persons to destroy standing corn in the fall of 1923. Those found, for the most part in small back-yard gardens, often showed evidence of extensive feeding by birds. Thus a small plot of about 1,500 hills of standing corn in Wakefield, Mass., showed that birds had removed a very high percentage of the larvae from the stalks. In various localities stubble and stalks lying on the ground were shredded and many larvae no doubt removed.
As far as these observations were possible, they coincide with the results obtained in the experimental work already described.
The question has been asked whether birds know that infested cornstalks contain larvae or whether the feeding that they do is more in the nature of an accident. Beside the ex- periment at Medford, Mass., mentioned in table 3 from which birds are credited with removing 68 per cent of the larvae a like experiment was placed in the fall of 1923, similar in every respect



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19251
Efficiency of Birds in Destroying Larva of Corn Borer 43
except that the cornstalks showed no trace whatever of infes- tation by the European corn borer. Spring examinations showed that whereas birds had fed extensively on larvae in the infested stalks, there were only one or two shallow incisions that might be credited to birds in the stalks that were ent'irely free from infestation by this insect. These uninfested stalks were, there- fore, probably examined by the birds but the experiment showed that they were soon undeceived as to the fact that these stalks, although so much like the nearby infested ones in appearance, contained no larvae of the corn borer. Field observations have shown that birds also feed in the spring on the pupae of this insect, the nature of the feeding being similar in every respect to that described in the case of their feeding on larvae. In some cases portions of the pupae remain in the burrows of the insect as if the birds were not entirely pleased with the change that its food supply had undergone.
These studies have been confined mostly to the feeding by birds on the larvae of the European corn borer in the fall, winter and spring, at which time the insect is in overwintering quarters within the host plant, because no such extensive feeding has been observed during the growing season. Adults of the insect are active only at night, resting during the day on the under sides of leaves unless disturbed when their flight is short and low and is to the nearest cover from the seat of disturbance. The larvae for the greater part of their lives feed hidden within the food plants, leaving their burrows infrequently except during the warmer nights of midsummer. It is known, however, that birds readily take the adult of the insect although observations seem to indicate that up to the present time they have not taken larvae from growing plants in any noticeable numbers. On two occasions, during studies of the capabilities of flight of the moths, birds took the flying insects to such extent as to interfere seriously with the success of the experiments. It is probable, therefore, that the reason that they do not feed more extensively on the moths is not because of any distaste for them, but because of the inactivity of-the moths during the hours of sunlight. Since the larvae of the European corn borer in the over- wintering condition are nearly destitute of hairs and the skin is



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44 Psyche !February
rather thin and sparingly chitinized, they are ideal food for birds. Furthermore, at this time of the year the body of the larva is filled with so-called fat body so that the insect becomes food of the highest value with only a small portion of waste matter. The larvae in standing stalks, during times of heavy infestation, provide a plentiful supply of food for birds, such as woodpeckers, during the winter, provided the stalks are not completely covered with snow, at a time when other food is scarce. They also provide a source of food for migrating insectivorous birds in the spring, especially those arriving early before other insects become active and available in abundance. There is. therefore, every reason to hope that birds will take advantage of this food supply to the benefit not only of themselves, but also of man. This they may readily do, provided that they are able to locate the larvae in the stalks, as these experiments seem to indicate they are doing more and more, and if they are able to remove the larvae from the stalks after finding them, a feat of which not all insectivorous birds will be capable. However, there is ample evidence to indicate that their industry may help to hold the insect partially in check, or even so to reduce its numbers in some localities during t,he winter and spring that damage by the species may not be extensive enough to cause heavy loss to crops in such localities the following summer.
Summary.
Evidence of feeding by birds on larvae of the European corn borer has been found each spring for several years in New Eng- land. Such work was of two distinct types; the work of wood- peckers, particularly the downy woodpecker, which drills holes into standing stalks in order to reach the overwintering larvae of this insect; and work by grackles, blackbirds, starlings and other species which shred stalks that have fallen over and devour the hiding larvae.
For the most part such feeding by birds has been confined to localities that have been heavily infested for several years, the extent of such feeding having been found to vary greatly, but counts have shown that in some fields of sweet corn over



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19251
Efficiency of Birds zn Destroying Larva? of Corn Borer 45
90 per cent of the overwintering larvae have been removed from the stalks.
Experiments where infested cornstalks were placed in rep- resentative localities in the infested area of New England in the fall of 1922 and 1923 were examined the following spring in each case, before larvae had become active. These experiments were for the purpose of determining whether or not the habit of feeding on larvae of this insect was general. The experiments
examined in the spring of 1923 showed that of 18 localities the cornstalks of which were recovered in good condition, birds had fed extensively on larvae contained in the cornstalks of 5 locali- ties, the proportion of larvae credited to such feeding ranging from 12 percent to 84 per cent, and averaging 61 per cent for these 5 localities and 17 per cent for the whole 18 experiments. Examined in the spring of 1924 showed that of 47 local- ities the cornstalks of which were recovered in good condition, birds had fed extensively on the larvae contained in the cornstalks of 16 localities, the extent of such feeding ranging from 19 percent to 78.5 per cent. The average proportion of larvae taken from these 16 localities was 54 per cent and the average of larvae taken from the whole number of 47 localities was 19 per cent. The feeding, which was mostly the work of woodpeckers, was found to be over a much more extended area in t'he spring of 1924 than in the spring of 1923. Feeding by woodpeckers on the'larvae of this insect over- wintering in sunflower, (Helianthus annuus L.), Princesplume (Polygonum orientale L.), Polygonum sp., and cocklebur (Xan- thium spp.) have also been found in experiments and in barnyard grass (Echinochloa crusgalli L.) and cocklebur (Xanthium spp.) in the field.
The importance of the feeding by birds on overwintering larvae of this insect at the present time, taking the infested area in New England as a whole, is not great, but in small areas the importance of their feeding must be considerable, since these small areas are often very heavily infested. The important point at present is that birds are finding the overwintering larvae of the corn borer, that they are feeding on them, and that such feeding seems to be on the increase.




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Psyche
At left.
The appearance of corn stalks after woodpeckers have fed on the larvae of the European corn borer that the stalks harbored. The section
to the right shows the holes made by these birds in reaching the larvae. The two sections to the left are of one corn stalk split open to show the condition of the center of the stalk, all the larvae having been removed by these birds.
At right.
Corn stalks infested by the European corn borer showing the appearance of the stalks after birds such as blackbirds and grackles
have broken them open and devoured the larvae that they contained.



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PSYCHE 1925 VOL,XXXll. PLATE I.




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