Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 23, 2001
Publication Date: March 1, 2002
Interpretive Summary: Silverleaf whiteflies are a major pest of cotton and other commodities in the Southwestern region of the US. This insect can reproduce on a wide range of plant species and the rate of reproduction can be prodigious. The supply of dietary nitrogen to the insect is thought to be a limiting factor in the development of the insect, but little basic scientific information is available regarding the interaction between plant nitrogen nutrition and nitrogen acquisition and metabolism by the whitefly. We have demonstrated that plant nitrogen status has a major impact on whitefly nitrogen metabolism. Within three days of feeding on a nitrogen-deficient cotton plant, amino acid excretion by the insect ceased, and the levels of amino acids in the insect bodies was markedly decreased. The amino acid glutamine was most impacted by plant nitrogen nutrition and this amino acid appeared to play a key role in general amino acid metabolism of the insect. Additionally, it was discovered that the amino acid asparagine was the major component of excreted nitrogen thus indicating a key role for this amino acid when whiteflies have an abundant supply of dietary nitrogen. Finally, it was discovered that whiteflies contained large amounts of methionine sulfoxide, an oxidized form of the essential amino acid methionine that may be part of a mechanism that protects insects against oxidative stress. This research will be useful to private and public scientists investigating metabolic mechanisms that could lead to novel control methods for homopteran insects.
Technical Abstract: The effect of plant nitrogen (N) status on the content and distribution of free amino acids in the bodies and honeydew of silverleaf whiteflies Bemisia tabaci (Gennadius) Biotype B (= B. argentifolii Bellows and Perring) was determined. Whiteflies fed for four days on cotton leaves that received sufficient or deficient N fertility. At low-N fertility photosynthesis and leaf total N concentration were decreased, and a much-reduced level of free amino acids was recovered in phloem sap. Low N fertility did not affect whitefly total N concentration, but did markedly decrease the free amino acid content. Gln, ala and pro accounted for over half of the insect free amino acid pool, but N-deficiency had the largest impact on gln. Large amounts of amino N, especially asn, were excreted from whiteflies fed on N-sufficient plants whereas amino N excretion essentially ceased for the low N fertility treatment. The distribution of amino acids in the insects and honeydew was not closely related to the phloem sap amino acids. However, total amino acid excretion was quite indicative of the plant N status and the quality of the insect diet. The results indicated that whiteflies responded rapidly to plant N status, effectively reducing free amino acid pools and excretion of amino acids when feeding on N-deficient plants. Gln metabolism was central to the insect response to altered dietary N supply.