Progress 10/01/03 to 09/30/04
Outputs
Over the course of this grant, we examined dynamics of ovarian development in a walnut-infesting tephritid fly Rhagoletis juglandis. In this species, ovarian development is stimulated by the presence of host fruit. We have described in detail what happens in the ovaries as a consequence of fruit experience. Effects are manifested in terms of oogenesis; we never observed oosorption under the conditions of our experiments. Host experience increases both the number of ovarioles and increases in rate of development of first and second follicles within an ovariole (Lachmann & Papaj 2001). We ascertained that effects are much more pronounced in the first maturation cycle than in later maturation cycles (D. Papaj & H. Mallory, unpubl. data). We also determined that fruit experience enhances oogenesis by promoting protein uptake; sugar uptake was unaffected by fruit exposure (D. Mayntz & D. Papaj, in preparation). We also explored the stimuli involved in host-mediated
oogenesis. Despite intensive efforts with several olfactometer designs, we failed to find evidence that the odor of suitable fruit promotes oogenesis, or that the odor of unsuitable fruit (e.g., larval-infested fruit) suppresses oogenesis (D. Papaj, in preparation). We determined that a roundness effect published earlier was due to visual input, rather than tactile input. We determined that males also enhanced oogenesis in newly-emerged females and that the male effect was independent of the fruit effect (the effects are additive). We subsequently explored whether or not ovaries know best; that is, whether or not fruit experience affects oogenesis to a degree that is related to the suitability of the fruit for offspring survival. We determined that, with respect to some fruit quality indicators (fruit ripeness, size, and larval infestation), ovaries do know best (D. Papaj, Functional Ecology, in press): females mature eggs faster when fruit are ripe, large and uninfested,
respectively. A different pattern occurred with respect to host-marking pheromone, which is a signal of the presence of eggs in fruit: females matured eggs faster when fruit were marked than when they were unmarked. Aside from effects of queen pheromone on worker reproduction, this is the first evidence in insects of a pheromone affecting ovarian development. We have recently extended the theme of ovarian dynamics to consider how a females fruit experience affects mating behavior (L. Carsten and D. Papaj, Behavioral Ecology, in press). This extension is appropriate, given that the mating system is fruit-based. In two experiments, one which manipulated fruit presence, the other which involved topical treatment of females with methoprene, a JH analog, we determined that fruit experience influences difference components of mating in different ways. Propensity to copulate is affected by effects of fruit experience on oogenesis, whereas copulation duration is affected by fruit experience
in ways that are oogenesis-independent, and which may involve learning. A functional analysis of these patterns suggested that some reflect male-female conflict of interests whereas others reflect a pattern of mutual interests.
Impacts
Our work focuses on how the host resource influences ovarian development in females. Since pests cannot lay eggs if they have not made them, such information is crucial to predicting the impact of a pest population on a given crop.
Publications
- L.D. Carsten and D.R. Papaj. 2005. Effects of reproductive state and host resource experience on mating decisions in a walnut-infesting fly (Rhagoletis juglandis). Behavioral Ecology, in press.
- A.D. Lachmann and D.R. Papaj. 2001. Effect of host stimuli on ovariole development in the walnut fly, Rhagoletis juglandis (Diptera, Tephritidae). Physiological Entomology 26:38-48.
- D.R. Papaj. 2005. Ovarian dynamics in relation to host quality in the walnut-infesting fly, Rhagoletis juglandis. Functional Ecology, in press.
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Progress 10/01/00 to 09/30/01
Outputs
In work preliminary to this grant, we discovered that fruit stimuli enhanced oogenesis in the walnut-infesting tephritid fly, Rhagoletis juglandis, in the first egg maturation cycle. These findings provided the basis for the work in this grant. Using this species as a model, we are examining how host availability and host quality in terms of fruit size, ripeness, level of egg and larval infestation, and host species identity influences the dynamics of ovarian maturation. We further proposed to examine the interaction between ovipositional and ovarian dynamics. Finally, we proposed to use the information obtained on ovarian dynamics to construct a model that predicts levels of infestation over varying conditions of host quality and abundance under field and field cage conditions. In this first year of our grant, we first undertook an analysis of events at the level of the ovariole that are influenced by host stimuli. We found that fruit stimuli enhance oogenesis, with
oosorption playing no discernible role. Fruit stimuli cause a slight but significant increase in the number of ovarioles, but the main effect is to cause each ovariole to mature follicles more rapidly (Lachmann and Papaj 2001). In other work, we determined that the proximate effect of fruit stimuli is to promote protein intake by females which is essential to egg production; there is no effect on carbohydrate intake (D. Mayntz and D. Papaj, in preparation). We also evaluated the nature of fruit stimuli involved, including tactile and odor stimuli (E. Hebets and D. Papaj, in preparation). Work on the first objective, especially the role of fruit quality, has gone extremely well. For instance, large fruit and large surrogate models promote oogenesis significantly more than small fruit and models. Unexpectedly, host-marking pheromone, which deters oviposition, was found to have an enhancing effect on ovarian development. These results are being prepared for publication.
Impacts
A pest population's attack potential is a function both of the population size of the pest and the fecundity of females in the population. Our work focuses on factors, specifically the host resource, that influence female fecundity. Such information is expected to be useful in predicting attack potential.
Publications
- A.D. Lachmann and D.R. Papaj. 2001. Effect of host stimuli on ovariole development in the walnut fly, Rhagoletis juglandis (Diptera, Tephritidae). Physiological Entomology 26:38-48.
- M. Aluja, F. Diaz-Fleischer, D.R. Papaj, G. Lagunes and J. Sivinski. 2001. Effects of age, diet, female density, and the host resource on egg load in Anastrepha ludens and A. obliqua (Diptera: Tephritidae). Journal of Insect Physiology 47:975-988.
- D.R. Papaj. 2002. Effects of host quality on ovarian development parallel effects on oviposition behavior. Work completed.
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