Domesticated wheat alters biological control of aphids

The domestication of wheat has altered the interaction between the aphid Rhopalosiphum padi and the parasitoid Aphidius colemani. Researchers compared a wild wheat genotype collected on Mount Carmel in Israel with the domesticated cultivar 'Galil', used in the same region. The results indicate distinct effects on the pest and its natural enemy (DOI 10.3390/insects17070704).

The initial hypothesis predicted greater aphid performance on domesticated wheat and less parasitism in this material. The greenhouse experiment showed a more complex pattern. At low density, wild wheat favored a faster increase in the Rhopalosiphum padi population. After three days, wild plants had an average of 71,6 aphids per plant. Domesticated plants had an average of 56,1 aphids per plant.

Introduction of the parasitoid

This trend changed after the introduction of the parasitoid. Twelve days later, the domesticated plants supported larger aphid populations. The study recorded approximately 780 aphids per plant in domesticated wheat and approximately 420 aphids per plant in wild wheat. The difference occurred despite the higher parasitism in the domesticated plants.

The parasitoid Aphidius colemani performed better on domesticated wheat. The number of mummies formed per plant doubled in this material compared to wild wheat. The percentage of parasitism was also higher. In domesticated plants, 85,3 percent of the mummies originated from adult parasitoids. In wild plants, this rate reached 53,2 percent.

The number of offspring of the parasitoid also changed according to the wheat genotype. Domesticated plants produced 2,7 times more adult wasps. The difference resulted mainly from the greater number of males that emerged in this material. The total production of females did not differ between the two types of wheat. Even so, the effective proportion of females was higher in wild wheat.

Study characteristics

The researchers used seeds of Triticum turgidum subsp. dicoccoides as wild wheat. The material came from a natural population near Beit-Oren, Israel. The 'Galil' cultivar of Triticum aestivum represented domesticated wheat. Both materials exhibit late maturation.

The plants received six adult Rhopalosiphum padi. ​​After three days, a female Aphidius colemani was introduced into each cage for two hours. The researchers monitored the formation of mummies, the emergence of parasitoids, and the growth of aphid populations. The plants remained in a greenhouse with a temperature of 25 degrees Celsius, with a variation of three degrees Celsius.

The study also measured plant biomass. At the end of the experiment, domesticated wheat showed a higher dry weight of the aerial part. The average reached 302 milligrams, compared to 179 milligrams in wild wheat. The final density of aphids per biomass did not differ statistically between genotypes. Even so, the final total population of aphids was higher in domesticated wheat.

Different mechanisms

The data suggest different mechanisms of population limitation. In wild wheat, competition among aphids may have limited the pest's growth to high densities. In domesticated wheat, parasitoid activity appears to have exerted greater pressure on the population.

The researchers emphasize caution in the interpretation. The study evaluated only one wild genotype and one domesticated genotype. The number of replicates was also reduced. Even so, the organisms used came from the same geographic region, with a history of association. This condition increases the ecological relevance of the observed interactions.

The conclusion points to varying effects of domestication on pests and natural enemies. Domesticated wheat favored a larger final population of aphids, but also increased biological control by Aphidius colemani. This control may partially compensate for infestation by Rhopalosiphum padi in wheat cultivars.