And the fact that I mentioned the control as generally as I did is of significance in that all of these flies of the various species are apparently susceptible to the same type of control measure.
As far as the host plants are concerned, I have personally observed injury on all of our common Juglans species that I have run across in New York State and in some of the states to the south of us, including butternut, Japanese walnut, English walnut and black walnut. I have seen reports of infestations which were recorded in hickory, but I personally have not seen them.
I'd just like to have a show of hands. How many in the audience here have had experience with the walnut husk maggot or had injury on the fruit? (Showing of hands.) I see the majority of you certainly know what it is, but just as a brief reminder, the type of injury, of course, varies somewhat depending possibly on the variety and time of year at which the fruits first become infested. We know, of course, that the flies do not begin to puncture the husk until they attain a certain degree of softness. Early in the season they are not able, apparently, to penetrate the husk with the ovipositor, and that, of course, varies not only with hardness but with varieties. The flies, of course, may be seen on the fruit even though they are not able to penetrate the husk and deposit their eggs. These husks, of course, many of them, become dry and hard after they have been tunnelled out, and it is almost impossible to clean the shells. Occasionally you have nuts in which you have a separation of the suture, and in those cases you very frequently get the exudate from the husk penetrating through the suture in the shell onto the kernels themselves, and in those cases molds may grow on the kernels so that those fruits are no good.
In connection with this injury I am going to show you some slides in a few minutes, but the preceding speaker made reference to a type of injury which occurred on the terminal growth of a walnut tree and that is one that we have had a lot of inquiries at the Experiment Station about, injury to the new terminal growth fairly early in the season. That probably, in most cases, is caused by the butternut or the walnut curculio. Early in the season these adults begin feeding on the new terminal growth, and they even puncture the new growth and lay their eggs there before the nuts are large enough for them to attack and very often considerable killing back of the terminal growth occurs. I have seen it on English walnut seedlings in nursery rows where there would be very large kill-back from the walnut curculio. Superficially the injury on the fruit is quite similar to that of the husk maggot.
(First slide.) This first slide is just to give you some idea of the general areas of fruit growing and distribution in New York State. The eastern section, right-hand side, Champlain Valley and Hudson Valley, are primarily apple maggot regions. Some walnut husk fly probably occurs there, but they are predominantly apple-growing areas. In the central part of the state, northern, particularly, we have fruit, and as far as I know, there are no plantings of walnuts there, though you people may know of some. In The Ontario Plains section south of Lake Ontario is one of our big fruit belts in the State. Some walnuts are also grown here. Consequently this area has in it apple, walnut and cherry maggot flies, and, of course, they will be lapping over in all those areas into surrounding territories. But this gives you an idea, in a general way, of the distribution of the host plants and the flies about which I have been speaking.
(Next slide.) Those flies get pretty big when you get them up there. They are not that easy to see in the field. The ones on the top are the species found on cherries. The one on the lower left is the apple maggot, the one on the lower right is walnut husk maggot. The only difference you can see here is in the wing pattern but in nature they differ in color. They all have a little different wing pattern. Also, there is a little difference in size, the walnut husk maggot being the biggest of the four species shown here.
(Next slide.) I have shown here the emergence date of the various species, including the cherry fruit flies, the apple maggot and the walnut husk fly. And you notice that beginning over about the first week in June you have emergence of the cherry fruit flies, and you have a continuance of emergence of some of these species up until at least the first or second week in August. These points going up and down just show the number of flies that were taken on given dates, and there is a very definite correlation between the proportion of flies that emerge on any given day with the temperature or moisture condition. Some years, when you have very hot, dry weather, there is considerable mortality of these flies as they just do not seem to be able to emerge from the soil, which is a good thing.
(Next slide.) This photograph is one that I wasn't sure I was going to get back in time for the meeting, but it is a Kodachrome of a pair of flies mating on an English walnut. This happened to occur on some of our own trees at the station, so that we are not immune from attack by this bug.
(Next slide.) That is a close-up of an egg puncture, just a very tiny little hole in the husk, and once in a while they lay an egg even on the surface. Those eggs are quite small, about a millimeter in length and about two-tenths of a millimeter in width, but the next slide will show you that what they normally do is to put them inside that puncture in groups. They vary quite a bit, but the average number of eggs is about 20 in each puncture. But that doesn't mean you won't have maybe four or five different punctures on a given nut, so you may end up with at least a hundred or more maggots in a shuck.
(Next slide.) And the next picture is a photograph of the same English walnut taken about six or seven days later, showing the young maggots that have just hatched out. What they will do, they will begin boring in, and they will just radiate out in all directions into the shuck. When they have gotten that far along, of course, there is no hope for control.