Biological Activities of Extract Mixtures of Tephrosia vogelii (Leguminosae) and Annona squamosa (Annonaceae) against Crocidolomia pavonana.

Abstract

The use of botanical insecticides is one of pest control tactics that has several advantages, such us easily biodegradable in the environment, slow development of insect resistance, synergism of extract components so that they are more effective, short persistence, and generally safe to non-target organisms. Insecticidal properties of Tephrosia vogelii leaf and Annona squamosa seed extracts have been well established, but the evaluation of toxicity, effect on fecundity, and effect on oviposition of T. vogelii and A. squamosa extract mixture against Crocidolomia pavonana has not been done. The objectives of this study were to evaluate the toxicity, effect on fecundity, and effect on oviposition of T. vogelii leaf extract and A. squamosa seed extract and their mixtures against C. pavonana. In the toxicity test, ethyl acetate extract of T. vogelii leaves and methanol extract of A. squamosa seeds and their mixtures were tested by a leaf-dipping method against second-instar larvae of C. pavonana. Each test extract was tested at six concentration levels in the range of 0.025%-0.190% and 0.004%-0.020% for T. vogelii and A. squamosa extracts, respectively. The extract mixture was tested at three concentration ratios, i.e. 1:1, 9:1, and 1:9, with concentrations ranges of 0.0050%-0.0400%, 0.025%-0.200%, and 0.004%-0.020%, respectively. Each treatment and control were replicated five times. Observation was conducted from 24 to 96 hours after treatment (HAT). The number of dead larvae was recorded. Larval mortality data was analyzed by probit method using POLO-PC. The fecundity test was conducted using T. vogelii and A. squamosa extract and their mixture which has the highest toxicity at LC25 and LC50 levels. Treated leaves were fed to second, third, and fourth instar C. pavonana larvae by a leaf-dipping method for 48 hours. The emerging adults were paired to obtain 15 pairs for each test concentration and control. The number of eggs laid each day was collected and counted. The adults were maintained until death. The total egg production and the fecundity per day were analyzed using analysis of variance followed by Duncan's multiple range test (α = 0.05). The tests on antioviposition effect was conducted using T. vogelii and A. squamosa extract and their mixture with a concentration ratio of 1:9 at LC99 and 2 x LC99 levels. The test extracts were prepared in the same way as in the toxicity test. Broccoli plants used were 1 month old (possessing 5 leaves) and 2 month old (possessing 8 leaves). Broccoli plants were sprayed with extract preparations until run-off. Four broccoli plants consisting of 2 treated broccoli plants and 2 control plants were placed alternatingly in a plastic cage. Two pairs of 3 day old adults of C. pavonana were introduced into the cage and allowed to oviposit for 2 days. The number of eggs laid on treated plants and control plants were compared with paired t-test. viii The results show that the mortality of C. pavonana larvae as a result of the treatment with T. vogelii extracts and A. squamosa extracts and their mixtures increased with the increase in extract concentration and observation time. T. vogelii extract is highly toxic and A. squamosa extract is very highly toxic to C. pavonana larvae. T. vogelii extract had a lower toxicity than A. squamosa extract with LC50 of 0.068% and 0.007%, respectively. The treatment with T. vogelii and A. squamosa extract mixture at the concentration ratio of 1: 9 had the highest toxicity (LC50 0.008%) compared with the other two concentration ratios (1: 1 and 9: 1; LC50 0.015% and 0.091%, respectively). The extract mixtures at the concentration ratio of 1:1 at the LC50 level at 72 and 96 JSP and that of 1:9 at the LC50 and LC95 levels had additive joint action, whereas that at the concentration ratio of 9:1 had antagonistic joint action against C. pavonana larvae both at LC50 and LC95 levels. The treatment with A. squamosa extract and its mixture with T. vogelii extract at LC50 significantly reduced the fecundity of C. pavonana adult females that developed from larvae treated as fourth-instar, but did not significantly affect the fecundity of the females developing from larvae treated as second and third instars. The decrease in the number of eggs in the LC50 treatment of A. squamosa extract and its mixture with T. vogelii extract was 70.4% and 71.4% respectively, compared with egg production in the control females. The treatment with T. vogelii extract at LC99 and 2 x LC99 significantly inhibited oviposition by the C. pavonana females on broccoli plants one and two months after planting with oviposition inhibition indices of 91% and 94% on one month old and 88% and 78% on two month old broccoli plants, respectively, whereas the treatment with its mixture with A. squamosa at 2 x LC99 significantly inhibited the oviposition only on one month old broccoli plants with oviposition inhibition index of 58%. Based on the results presented above, it can be concluded that T. vogelii extract and A. squamosa extract as well as their mixtures are potential to be used for the control of C. pavonana pest.