INTERACTIONS OF THE HESSIAN FLY, THE BIRD CHERRY OAT APHID, THE ENGLISH GRAIN APHID, AND SELECTED WHEAT VARIETIES (R. PADI, S. AVENAE, ABE)

VACHAROBON THIRAKHUPT, Purdue University

Abstract

There were preferences of the bird cherry oat aphid, Rhopalosiphum padi L. on Hessian fly infested plants of 'Knox 62', 'Monon' and 'Seneca' when compared to the non-infested controls. Among them Monon was always the least preferred as determined by the numbers of aphids found on the plants during a five-day period after introduction. However, varietal differences existed even in control plants, and Monon along with 'Blueboy' were never the preferred hosts. Feeding on fly infested wheats caused aphids to mature early, but did not enhance the longevity and fecundity of the aphids. The intra- and interspecific relationships of R. padi and the English grain aphid, Sitobion avenae (Fabr.) were dependent on the population density. Five, 10 and 15 aphids were used. The higher the density, the longer the developmental period. The longevity and fecundity changes varied and were not consistent. Competition seemed to be evident when the two species were in the same population. In a mixed population, longevity and fecundity of both aphids greatly declined when there were 10 and 15 aphids of each species in the populations. S. avenae needed a longer time to develop from nymphal to adult stage than R. padi, but had a much longer reproductive period and a longer life at all density levels. The differences in fecundity were notable in mixed populations of 10 + 10 and 15 + 15. Life tables and survivorship curves of both species resembled the hypothetical type I of the general curves. High mortality rates were found when aphids were about eight weeks old. No R. padi survived longer than 10 weeks and no S. avenae longer than 12 weeks. The finite rates of increase ((lamda)) for aphids in all density levels were above 1.1, providing the optimum conditions in the laboratory (20 C and 14:10 hour photoperiod). Both viruliferous (PAV strain of BYDV) and non-viruliferous R. padi and S. avenae caused yield losses to some degree in 'Abe'. For the three infestation levels studied, five aphids per plant was the minimum that caused 1000-grain weight reductions, but the effects on other yield components varied. The grain numbers were high in infested plants, but the grains were generally shrunken. Infestations of S. avenae and mixed population at the heading stage of Abe caused greater losses than other treatments. The preference of S. avenae for feeding on heads once emerged may be a key factors for high losses. The interactions of the mixed population probably rely on S. avenae feeding in this particular circumstance.

Degree

Ph.D.

Subject Area

Entomology

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