Effect of different maturities of starfruit on the ovipositing of Bactrocera dorsalis and comparative analysis of volatile components

Abstract:【Objective】Bactrocera dorsalis (Hendel) (Tephritidae:Diptera) is a major pest of fruit crops.Itis highly polyphagous and causes economic losses to a wide range of fruit crops, consisting of more than 250 species of fruit and vegetables.The insect has a strong reproduction capability, with each female ableto produce 400-1 800 eggs.Female B.dorsalis lay their eggs in mature fruits, while they are still on thetree, which causes the fruit to rot and fall in advance.Thus, oviposition is the main cause of serious harmto fruits and vegetables by the female B.dorsalis.Therefore, oviposition from the female B.dorsalis will bethe key entry point to control any potential harm from B.dorsalis.At present, the control method to useagainst B.dorsalis is primarily induced and chemical control.However, B.dorsalis have developed astrong resistanance to a variety of chemical pesticides.Therefore, the control effect of chemical pesticidesis greatly reduced.Pesticides can seriously affect environmental safety.But the effective attractant, methyleugenol, is primarily used to lure and control the male B.dorsalis.It has been reported that methyl euge-nol is not only a safety hazard to the ecological balance, but also may induce liver cancer in mammals.Therefore, the search for a new attractant in the host fruit will be an effective way to control B.dorsalis.The attractive effects of various host fruit volatiles on the female flies have been reported.Starfruit is oneof the important hosts of B.dorsalis.There previously has been no report on the research of the ovipositionlure of starfruit to female B.dorsalis.In this paper, the effect of two different maturities of starfruit (yellowripe starfruit and green ripe starfruit) on the oviposition of female B.dorsalis and the differences of theirvolatile components of yellow and green ripe starfruit were compared and analyzed using a solid phase mi-croextraction-gas chromatography-mass spectrometry (SPME-GC-MS) .It was also speculated that theyellow ripe starfruit contains the volatile substances that induce the oviposition activity of the female B.dorsalis.The paper will provide a scientific basis for the exploration of the oviposition attractant to the fe-male B.dorsalis.【Methods】The difference in the amount of eggs laid by female B.dorsalis between yellowand green ripe starfruit were analyzed by using a spawning cup.The spawning cup was made of disposableplastic and used to fill holes with insect needles.Two spawning cups were placed in the diagonals of thefeeding cage and in the bottom of each spawning cup was placed an equal amount of yellow and green ripestartfruit as a treatment and control, respectively.In the experiment, 1, 5, 10, 20 and 40 g yellow andgreen ripe startfruits in each spawning cup were tested as different treatments.Each treatment was repeat-ed 3 times, and after 24 h, the spawning cup was removed to check the amount of eggs laid by the female B.dorsalis.The yellow and green ripe starfruit were sealed in 250 mL sample bottles for the gas volatiliza-tion process.After 15 min, the volatiles from the yellow and green ripe starfruit were collected by usingthe solid phase microextraction (SPME) sampling technique.The comparative analysis of the volatile com-ponents from yellow and green ripe starfruit was identified by applying the gas chromatographic-massspectrometric (GC-MS) method.All test data were statistically analyzed and processed using Excel, andSPSS 22 software to determine the significance of the test data.【Results】The amounts of eggs on the yel-low ripeness starfruit were significantly higher than those on the green ripe starfruit in every treatment (1, 5, 10, 20 and 40 g) .It was determined that the yellow ripe starfruit had significant oviposition attractantactivity for the female B.dorsalis.The amount of eggs was increased with the increase of the weight of theyellow ripe starfruit.When yellow ripe starfruit was 1, 5, 10, 20 and 40 g, the oviposition capacity was (5.7±0.7) , (8.0±0.6) , (24.0±1.2) , (45.0±1.7) and (48.0±1.2) grain per cup, respectively.The results showedthat the chemical composition and content of the volatile from yellow and green ripe starfruit were differ-ent.30 volatile compounds were detected in yellow ripe starfruit, while only 24 volatile compounds weredetected in green ripe starfruit.The volatile chemical components of the yellow and green ripe starfruitwere primarily esters and caryophyll derivatives.Esters were primarily methyl hexanate, 2-Hexen-1-ol, acetate and methyl heptanate.The content of 2-Hexen-1-ol, acetate was the largest, accounting for 68%-84% of the total ester.The derivatives of the ring caramenes were primarily of megastigma-4, 6 (Z) , 8 (Z) -triene, which could be a characteristic compound of starfruit.A variety of compounds in yellow ripe star-fruit were not detected in green ripe starfruit.In addition, the contents of these 7 substances (methyl hex-anoate;2-Hexen-1-ol, acetate;beta-cis-ocimene;methyl octanoate;beta-Ionone;methyl heptanoate;megastigma-4, 6 (Z) , 8 (Z) -triene) in yellow ripe starfruit were significantly higher than those in green ripestarfruit.【Conclusion】Yellow ripe starfruit can induce the female B.dorsalis to lay eggs.The resultsshowed that the yellow ripe starfruit had some specific chemical substances that induced the female B.dorsalis to oviposition.The contents of methyl hexanoate;2-Hexen-1-ol, acetate;beta-cis-ocimene;methyl octanoate;methyl heptanoate;beta-Ionone and megastigma-4, 6 (Z) , 8 (Z) -triene in yellow ripestarfruit were significantly higher than those in green ripe starfruit.So, it can be speculated that these com-pounds possibly were attractive components that entice female B.dorsalis to oviposition.