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1 June 2003 Behavioral Changes in Japanese Beetle and Masked Chafer Grubs (Coleoptera: Scarabaeidae) After Parasitism by Tiphiid Wasps (Hymenoptera: Tiphiidae)
M. E. Rogers, T. J. Cole, S. B. Ramaswamy, D. A. Potter
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Abstract

We studied effects of parasitism by two Tiphia species (Hymenoptera: Tiphiidae) on burrowing behavior of their respective scarabaeid hosts and tested the hypothesis that parasitoid alteration of host hormones accounts for the observed behavioral change. In turf field-plots, third-instar masked chafer grubs, Cyclocephala sp., parasitized by native Tiphia pygidialis Allen burrowed to depths of 12–16 cm within 21 d, whereas nonparasitized grubs remained in the upper 4 cm of soil. Grubs bearing an egg or early-instar Tiphia larva were found relatively close to the surface, whereas those with a fourth- or fifth-instar parasitoid were deeper. Experiments in soil-filled, vertical observation chambers confirmed downward movement by parasitized Cyclocephala, and similar response in third-instar Japanese beetle, Popillia japonica Newman, parasitized by Tiphia vernalis Rohwer. Removal of the Tiphia egg from masked chafers was followed by initial downward movement of grubs and then a gradual ascent, suggesting that host behavior is affected both by the venomous sting and feeding by the wasp larva. Significant but inconsistent differences were found in juvenile hormone-III (JH III) titers in hemolymph taken from nonparasitized grubs or grubs parasitized for 1 or 14 d. Topical application of JH III and methoprene acid resulted in grubs moving deeper into the soil, whereas injection of 20-hydroxyecdysone did not affect grub behavior. Failure to dig deeply enough in soil when sampling for parasitized scarab grubs or Tiphia cocoons likely will result in underestimation of parasitism rates.

M. E. Rogers, T. J. Cole, S. B. Ramaswamy, and D. A. Potter "Behavioral Changes in Japanese Beetle and Masked Chafer Grubs (Coleoptera: Scarabaeidae) After Parasitism by Tiphiid Wasps (Hymenoptera: Tiphiidae)," Environmental Entomology 32(3), 618-625, (1 June 2003). https://doi.org/10.1603/0046-225X-32.3.618
Received: 7 August 2002; Accepted: 1 December 2002; Published: 1 June 2003
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KEYWORDS
Cyclocephala sp.
Popillia japonica
Scarabaeidae
soil insects
Tiphia pygidialis
Tiphia vernalis
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