Know Your Friends

Macrocentrus ancylivorus

Macrocentrus ancylivorus is a parasitoid native to northeastern portions of the United States. This braconid wasp was described in 1921 as a parasite of strawberry leafroller, but will attack many other caterpillars, such as fruitworms, stemborers and other leafroller species. It rapidly adapted to the Oriental fruit moth after that pest was introduced from Japan in 1913. In the 1930's M. ancylivorus was reared in large numbers and released in many areas of the East, Midwest and Canada, where it was not present or abundant, in an attempt to combat the oriental fruit moth infesting peaches and late-season apples. It was also later released in Western orchards. It is most effective in the area roughly from Massachusetts to Michigan and south to eastern Missouri, Arkansas and northern Georgia.

The 3-5 mm long adults are amber-yellow to reddish brown in color. The antennae and ovipositor of the female are as long as its body. They are active only when temperatures are between 65 and 80F; in the summer they often become active only at twilight and will oviposit throughout the night. M. ancylivorus also becomes inactive in low relative humidity (<40%). The female deposits eggs singly in the bodies of host larvae during its life span of less than two weeks. Up to 50 hosts may be parasitized. The wasps find their hosts by homing in on frass (caterpillar poop) rather than on the caterpillar itself, and will even try to oviposit in fresh frass, but not in free-crawling larvae. They prefer to oviposit in second and third instars. M. ancylivorus overwinters as first instar larvae in the hibernating host caterpillars. The larvae feed internally during the first three instars, then emerge to feed externally for the final instar. The wasp cocoon is spun in the cocoon of its host.

The seasonal cycle of the wasp is correlated with that of its host, with two or more generations per year depending on the host species. In New York M. ancylivorus has two generations on strawberry leafroller and 3-4 on Oriental fruit moth. Because the parasitoid takes about 7 days longer than its host to develop, the adults are emerging about the time of host egg hatch, ensuring that there will be host larvae available.

M. ancylivorus is one of the most important of at least 50 species of parasitoids attacking strawberry leafroller. As many as 7,600 wasps per acre of strawberry have been reported, with up to 60% parasitism. The effects of these parasitoids vary seasonally and geographically, with the greatest impact on overwintering larvae. The effectiveness of M. ancylivorus is reduced in some areas by hyperparasites.

M. ancylivorus can provide good control of Oriental fruit moth in peaches and apples. It is most effective against larvae infesting twigs rather than those in large fruits later in the season. Releases of 3 to 6 M. ancylivorus females per tree for the first and second broods of Oriental fruit moth effectively reduced damage by this pest on peaches. Releases work best if made as soon as the first wilted twigs are observed (although the wasps are not currently commercially available). This parasitoid could be used to enhance control of Oriental fruit moth in orchards using mating disruption or in combination with a reduced insecticide treatment schedule.

The parasite is most effective in controlling Oriental fruit moth in those orchards with a varied weed ground flora. Caterpillars of various species, feeding on the weeds, are an excellent reservoir for the parasite at times when its preferred host is unavailable. The ragweed borer (Epiblema strenuana), which bores in the stems of ragweed species, is a widely distributed alternate host. In New Jersey, M. ancylivorus is very common in strawberry leafrollers overwintering on various species of Rubus which frequently occur along roadsides, waste places and in cultivation.

- Susan Mahr, University of Wisconsin - Madison

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