Moth Photographers Group -- Mothtalk015. Htm

Mites may be either Parasites or Predators. As a parasite, mites use the host caterpillar or moth as a source of food in the form of hemolymph or "blood." They are usually seen as small fluid-filled "balloons," and there may be just one or a few on the dorsal or ventral surfaces of adult moths. Examples involve (left, above) a Yellow-spotted Renia, Renia flavipunctalis, and (center) Lettered Zanclognatha, Zanclognatha lituralis. A number of mite species feed on moths. Their parasitism is usually not fatal or disruptive to the development and reproduction of the moth larva, pupa or adults; but if the mites are exceedingly abundant they may have an effect on reproductive capacity of the female moth. Top right shows mites exploring a Dolichomia binodulalis prior to a blood meal.

In Troy Bartlett's photo at left a mite is in action as a predator, its prey being the eggs which will not survive having nutrients sucked out of them. So whether a mite is classified as a parasite or predator depends upon its effect on the organism. When it kills the host swiftly it is a predator. When it simply sucks blood without killing it is a parasite.
 

A third category is Parasitoidism for which examples are provided below. In the case of moths, parasitoids lay one or many eggs on or in a caterpillar. Upon hatching, the parasitoid larvae feed and develop within this single victim and emerge to pupate to adulthood. Invariably the caterpillar dies without completing its own life cycle. A true predator, on the other hand, feeds on and kills (usually as an adult) many items of prey.Another example are certain wasps that lay their eggs on adult spiders that they have paralyzed and the wasp larva then feeds on this live host, eventually killing it. A similar strategy is followed by wasps that lay an egg in a chamber they have constructed and then provision that chamber with a paralyzed caterpillar (or non-lepidopteran insect) which will be the sole sustenance of the juvenile wasp.
 

A late instar larva of the White-marked Tussock Moth, Orgyia leucostigma is shown at left, above, and an adult male (females are wingless) is shown at right. I shot the center photo at a milkweed patch about 100 yards from my house in Bowie, Maryland. It shows the corpse of a larva (nothing but skin and hairs) with the cocoon of an Ichneumon Wasp (>40,000 spp. worldwide: David L. Wagner) beside it. These were adhered to a milkweed leaf where the wasp pupa would remain until the following year. The wasp was most likely a member of the Campopleginae subfamily. The brown markings of the wasp's cocoon is fecal matter incorporated into it during its construction. I thank Anthony Thomas of Fredericton, New Brunswick, for telling me about the process and identifying the parasitoid. Here the parasitoid affected the host larva before it could pupate.

Joyce Gross shot a sequence of photos at Berkeley, California, of caterpillars and pupae of the Western Tussock Moth, Orgyia vetusta. It turned out that one of the caterpillars had been the recipient of the egg of a Tachinid Fly. An adult male Tussock Moth is shown at left, above (females are wingless). A late instar larva is shown next, followed by the corpse of a moth pupa with a viable fly puparium beside it. The fly maggot had developed within the moth caterpillar and let the caterpillar go into its own pupal stage before killing it. An eclosed adult Tachinid Fly is shown in the last photo. Here the parasitoid killed the caterpillar host after the host had entered the pupation stage. The parasitoid egg was laid on a leaf and the caterpillar subsequently ingested the egg while eating the leaf. Long hairs on caterpillars are a defense against parasitoids directly attacking the caterpillar but are no defense against an egg being ingested. Additional and larger photos in this sequence may be seen at this page.

This and the Cecropia Moth that follows offer an interesting contrast in evolutionary pathways of related but divergent species (the two Tachinid Flies). One, unable to lay eggs directly on a suitable host provides them instead on suitable foliage. The other plants vastly more eggs directly on very large caterpillars, glued on so that they can't be dislodged. Tony Thomas tells me he has probably seen 20+ flies emerge from one Cecropia host. If too many fly maggots are within a single caterpillar/pupa they will probably cannibalize each other to ensure that some flies reach maturity.

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Row 1: a. Adult Cecropia Moth. b. Late instar Cecropia caterpillar with general infestation of Tachinid Fly eggs; note adult fly in background. c. close-up of Tachinid Fly egg infestation.
Row 2: d. Typical adult Tachinid Fly (>20,000 spp. worldwide according to David L. Wagner). e. substantial fly egg infestation with blackened necrotic tissue. f. Tachinid Fly maggot.

Row 3: g. Typical silken Cecropia cocoon and egg-infested late instar larva. h. Opened cocoon with failed pre-pupa Cecropia larva. Note unhatched Tachinid Fly eggs and one Tachinid maggot. i. Tachinid maggots on ground (abnormally) below pupation site of moth larvae.

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