Studies On Efficiency Of Some Fumigants Against Some Stored Product Insects:

Refaat Abd El-shafy Mohamed

The objective of this work was to investigate theefficiency of phosphine, carbon dioxide alone and theirmixtures against some important insect species causingdamage to stored cereal grains and pulses in Egypt, namely:-E...:.. oryzae (L.), .!h dominica (F.) and.£.:. maculatus (F.).”he experiments were carried out in the laboratory at26±1’C, 6±1’C and 60±5% RH.A circulatory multi-flask apparatus was designedto prOVide a fumigation chamber suitable for the testinsects.’”R Phosphine was generated from PHOSTOXIN-pellets (productof DEGESCH Co. FR. of Germany).Carbon dioxide was prOVided as a pure gas of 99% ina pressure cylinder, which was connec ted with a pressureregulator.Results obtained could be summarized under thefollowing topics:-1. Efficiency of phosphine against Ysrious s.tsles of thetested insects:Fumigation tests were conducted with fixed concentrationsof phosphine (20. 40 and 80 vpm) at Yarying exposureperiods.”lht ~(esults ~~e4 showed that adults of h oryzae (L.),R. dominica (F.) and C. macu1atus (F.) proved to be themost susceptible stages to phosphine at 26±1·C and 6±1·C.The time of exposure was a more critical factor of dosagethan the concentration of phosphine.J fLow ”-v~ JPhosphine was ~more effective at higher temperatureagainst all stages of the three insect species tested thanat lower one. For example, with a concentration of 80vpm phosphine, the exposure times for 100% mortality incase of h oryzae were (0.9, 9.8, 8.7 and 8.0 days) at26±1·C and 3.3, 15.6, 12.3 and 47.0 days) at 6±1·C foradults, larvae, pupae and eggs, respectively.The corresponding values in case of .!h. dominica were(0.9, 26.4, 9.4 and 11.9 days) at 26±1”C and (4.9, 88.0, 159.3and 70 days) at 6±1·C for adults, larvae, pupae and eggs •were (2.6, 7.3, 10.3 and 18.9 days)at 26±1·C and (2.8, 39.5, 30.9 and 58.9 days) at 6±1·CThese valuesfor the various developllHlntal stages of £:.maculatus,respectively.By comparing the exposure time values required toobtain 100% kill for the different stages of the testedinsects at 26±loC and 80 vpm phosphine, it vas found that ----the adult stages of the various insects were .ore susceptibLeto phosphine than the immature stages. The adul ts of~ maculatus were much more tolerant to phosphine thanthe adults of both ~ oryzae and ~ aominica.Larval susceptibility to phosphine was in descendingorder C. maculatus·larvae, ~ oryzae-larvae and R. dominicalarvae.Pupae of ~ maculatus were somewhat more tolerantto phosphine than pupae of both ~ oryzae and R. dominica.Eggs of ~ maculatus were much more tolerant tophosphine than eggs of ~ dominica and ~ oryzae.2. Toxicity of carbon dioxide in controlled ataosphere (CA)to the tested insects:Studies carried out in the laboratory at 26±loC and6±loC to evaluate the efficacy of various CO2 concentrations(12.5, 25, 50. 75 and 100% v/v) in controlled atmosphere(CA) for controlling the various stages of ~ oryzae,~ dominica and ~ maculatus showed that carbon dioxidewas more effective at higher temperature than at lowerone and insect mortalities were increased generally asthe concentration of CO2 was increased.Adults of ~ oryzae were the most susceptible stageto CA contained various concentrations of CO2 followedby larvae, eggs and pupae. when the resul ts were comparedat the LTgO level and 26±1’C. The same trend was alsoobserved at the lower temperature for atmospheres containedCO2 concentrations between 12.5-75% v/v •Results revealed also that at the two test temperaturesadults of !.:. dominica were the most susceptible stage toCA contained CO2 at the LTgO level followed by larvae,eggs and pupae.By comparing the susceptibility of the different stagesof .£.:. maculatus at the LTgO level, it was found. that at26±1’C the order of tolerance to CA contained 25, 75 and100% CO2 was in decreased order pupae > larvae > eggs >-adults. At 6±1’C the order of tolerance to the variousCO2 concentrations was also pupae > larvae > eggs > adults.The lethal time values recorded for the adults ofthe tested insects at the lower temperature in CA contained100% v/v CO2 were higher than those obtained in CA contained75% v/v CO2 and this result could be due to nearly totaldepletion of oxygen in the CA of 100% CO2•3. Toxicity of mixtures of phosphine plus carbon dioxide tothe tested insects:The effect of addition of 25 and 50% CO2 to 20 and40 vpm phosphine was studied in the laboratory at 26±1’Cand 6±1’C for controlling the various stages of S. oryzae(L.), !.:. domioica (F.) and .£.:.: maoUilatus .(F.).obtained showed the following:Results• Time to mortalities were shorter at higher temperaturethan at lower one. • The adult stage of the tested insectswas the most susceptible stage to the mixtures of phosphine+ carbon dioxide at the two test temperatures.The lethal time values required for a certain mortalitywere generally reduced in the presence of carbon dioxideat the two test temperatures. For example at 26±loC thelethal exposure values needed to obtain 90% adult mortalitieswere ( 17, 16 and 22 hr) with 20 vpm PH3 alone and13, 4 and 14 hr} by a mixture of phosphine + 25% CO2 and(11, 7 and 5 hr) by a mixture of phosphine + 50% CO2 for~ oryzae, ~ dominica and C. maculatus, respectively.The corresponding values at 6±loC were (119,98 and122 hr) wi th phosphine alone, (50, 11 and 17 hr) bya mixture of phosphine + 25% CO2 and (41, 11 and 12 hr)by addition of 50% CO2 to phosphine, for the various insectspecies, respectively.For the larvae and at high temperature, times to 90%mortali ties were (51, 44 and 67 hr) with phosphine alone,(31, 35 and 66 hr) by phosphine + 25% CO2 and (29, 37 and28 hr ) by a mixture of 20 vpm PH3 + 50% CO2, for theforementioned insect species, respectively.The corresponding values at lower temperature were(162, 282 and 211 hr) with phosphine alone, (58, 94 and64 hr) by a mixture of phosphine + 25% CO2and (49, 49and 82 hr) by a mixture of phosphine + 50% CO2,For the pupae and at 26±1 DC, the lethal time valuesrequired for 90% kill were (51, 133 and 60 hr) by phosphinealone, (39, 70 and 43 hr ) by phosphine + 25% CO2and (43,69 and 58 hr) by a mixture of 20 vpm PH3+ 50% CO2’. forS. oryzae, ~ dominica and ~ maculatus, respectively.The corresponding values at 6±1 DC were (141, 267 and158 hr) by phosphine alone, (87, 95 and 113 hr) by phosphine+ 25% CO2 and (99, 83 and 122 hr) by a mixture of phosphine+ 50% CO2, for the forementioned insect species,respectively.For the eggs and at 26±1 DC, the lethal exposures for90% mortalities were (122, 133 and 120 hr) by 20 vpm PH3alone, (77, 62 and 68 hr ) by phosphine + 25% CO2and (61,37 and 44 hr) by phosphine + 50% CO2•, for the vario~s insectspecies, respectively.The corresponding values at 6±1 DC were (261, 278 and254 hr) with 20 vpm PH3 alone, (102, 119 and 119 hr) byphosphine + 25% CO2 and (106, 42 and 103 hr) by phosphine+ 50% CO2’ for the various insec t species, respecti vely.The same trend was also obtained with mixtures of40 vpm PH3 + 25 and 50% CO2the tested insect species atfor ~he jifferent stages of . . .the two test temperatures.Results revealed also that addition of CO2 to phosphineincreased the efficiency of phosphine at the LTSO levelinducing an additive or a synergistic effect on mortalitiesof the various stages of the insect species tested.At the LT99 level, theincreased also the efficiencyand larvae of h oryzae, R.addition of CO2 to phosphineof phosphine against adultsdominica and C. macu1atus.But for pupae and eggs, the addition of CO2 tophosphine induced, in some cases, an increase in theefficacy of phosphine. and in other cases an antagonisticeffect was obtained.