Aktivitas Insektisida Ekstrak Buah Cabai Jawa (Piper relrojrac/lIl71, Piperaceae) terhadap He/ope/tis antonii Sign. (Hemiptera: Miridae)

Abstract

Helopeltis antonii Sign. (Hemiptera: Miridae) is an important pest of cocoa, tea, and cashew nuts. This insect pest sucks shoot and nut saps of plants causing blackish brown spots. Application of synthetic insecticides is commonly used to control Helopeltis spp. due to insecticide fast action. However, use of synthetic chemical insecticides can cause pest resistance and resurgence and outbreak of secondary pests, killing of non-target organisms as well as environmental contamination. Therefore, it is necessary to search for environmental friendly strategy to control H. antonii. The objectives of this study were to test the toxicity of Piper retrofractum extract to H. antonii adults, evaluate the effect of sublethal concentrations of the extract on the number of progeny nymphs of H. antonii, and to evaluate the persistence of the extract against mortality and oviposition of H. antonii. Cucumber was used as an alternate host for mass rearing and testing medium. The study was conducted in several stages: insect rearing, extraction, toxicity test, effects of sublethal, and persistency test. Toxicity test of P. retrofractum extract was conducted at concentrations of 0.05%, 0.10%, 0.15%, 0.20%, 0.25% and 0.3% based on the result of preliminary test. The extract was diluted in a mixture of acetone, methanol, and Tween 80 (5:5:5 v/v) [final concentration of 1.2%] and then diluted with distilled water until the desired volume. In addition, control solution was also prepared containing distilled water and a mixture of acetone, methanol, and Tween 80 (5:5:2 v/v) 1.2%. For each treatment, 10 individuals of H. antonii adults were used with five replications. The effect of sublethal test was conducted at concentrations equivalent to LC25 and LC50. The extract was sprayed on the whole surface of cucumber. Then the treated cucumbers and fourth instar nymphs were put in a plastic container (13 cm and diameter 14 cm) and the insects were held for 48 hours. After 48 hours, the treated cucumbers were replaced with untreated cucumbers until the nymphs became adults. The adult insects were then paired to obtain 10 pairs for each concentration level and control. Each pair of adult insects was placed into plastic containers and fed with untreated cucumbers. All of the adult insects were maintained until they died. Observations were made by counting the number of progeny nymphs in each treatment. Persistence test of P. retrofractum extract was conducted at concentrations of 0.49% (LC95), 0.98% (2 x LC95) and control ([aceton + methanol + Tween 80,5:5:2] + distilled water). The test extract emulsions were put into a clear glass spray bottle then exposed under sunlight for 7 hours/day from 08:00 to 15:00 pm for 0, 1, 3, and 5 days. These extracts were subsequently used for testing of the effect on mortality and oviposition of H. antonii. In the mortality test, P. retrofractum extracts that had been exposed under sunlight for 0, 1, 3, and 5 days were sprayed on H. antonii using a hand sprayer. Ten H. antonii adults were used v for each treatment and each treatment was replicated five times. The percentage of mortality was counted at 1, 2, 3, 4, and 5 days after treatment (DAT). Effect of extract on oviposition test was done by spraying sunlight exposed P. retrofractum extract on cucumber (diet) to complete wetness using a hand sprayer. Control cucumber was sprayed with control solution as in the toxicity test. This test used choice method, one treated cucumber and control cucumber were put in the same at plastic container (13 cm high, 14 cm diameter) then two pairs of 2 day old H. antonii adults were put in that plastic container. Total number of eggs laid on treated and control cucumbers were compared using paired t-test. Result showed that mortality of H. antonii adults which caused by P. retrofractum extract 0.05%-0.3% had occurred since 24 hours after treatment (HAT), and after that the mortality of the test insects did not increase markedly. LC50 and LC95 of P. retrofractum extract at 120 HAT were 0.20% and 0.49% respectively. Total number of nymphs progeny in the treatment with sublethal concentration of P. retrofractum extract 0.203% (LC50) was lower than that in the the treatment with the concentration 0.141% (LC25). P. retrofractum extract exposed to sunlight for 5 days was still effective against H. antonii adults (80% mortality) but was not effective in inhibiting female H. antonii in laying their eggs. Inhibition of oviposition by H. antonii adults were only observed in the treatment with P. retrofractum extract 0.98% (2 x LC95) exposed to sunlight for 0 and 1 day, with oviposition inhibition index of 22.7% dan 23.8% respectively. Further research on the effectiveness P. retrofractum extract is needed in order to assess its feasibility to be used for controlling H. antonii .