RELATIONSHIP BETWEEN CHEMICALS IN SOME MALVACEAE CROPS AND HOST- PREFERENCE BY PODAGRICA SJOSTEDTI JACOBY (COLEOPTERA: CHRYSOMELIDAE)

Abstract

Crops in the Family Malvaceae are attacked by similar pests at different stages of their development. One of such insect pests is Podagrica sjostedti Jac., a flea beetle, which is oligophagus in nature. Information on variations of its infestation level within Family Malvacaea and the influence of plant chemicals on these variations are scanty. This information is necessary for making appropriate decisions on non-chemical components of integrated pest management (IPM). Therefore, this study was carried out in the early season 2010, and was repeated within the same season. Its objectives were to determine the flea beetle preference among five (5) Malvacaeae crops and the chemical basis for the preference. A randomised complete block design (RCBD) was adopted with four replicates; the Malvacaeae crops trialled - okra, kenaf, red roselle, jute mallow and cotton represented the five (5) treatments. The five crops were established from seeds; from 3 weeks after planting, data were collected on the population of P. sjostedti and number of flea beetle-induced leaf holes, leaf area damaged and number of damaged leaves per plant. Significantly higher population of P. sjostedti was found on okra (7.90) compared to kenaf, red roselle and jute mallow; cotton however,  had the lowest population of this insect. The leaf area damaged was significantly higher (P < 0.05) on okra (0.34) than on other crops, while the least was observed on cotton. The leaf contents of the primary and secondary metabolites varied significantly among the 5 Malvaceae crops. There was a significant positive correlation between the following plant chemicals - phytate, terpenes, flavonoids, tannin and crude fat on one hand and insect population, and leaf damage on the other. The relationship between plant chemicals - crude protein, dry matter, alkaloids, steroids, phosphorus and iron - and insect population (and leaf damage) was negative. Okra plant was the most preferred crop to the flea beetles, while cotton was the least preferred among the crops trialled in the Family Malvaceae; the phagostimulants responsible appeared to be phytate, terpenes, flavonoids, tannin and crude fat.