Rice Weevil Larvae Research Articles

Insecticide effect of pennyroyal and rosemary essential oils on the rice weevil

The study aims at evaluating the potential insecticide essential oils from two plants of the family Lamiaceae pushing the spontaneous state in the Tiaret region (western Algeria). Insecticides tests were performed in the laboratory by the direct contact method. The results of these tests have shown that rosemary essential oil has remarkable insecticidal properties. They induced 100% mortality of adult rice weevils to 15 μ l dose after only 24 hours of exposition. The essential oil of pennyroyal induced 70 % mortality at the same dose and for the same exposure time. Lethal doses (LD50) are determined in the order of 5,58 for rosemary and 7,36 μ l for pennyroyal. The LD90 Are in order of 9.36 μ l it mean between the second and third dose tested for the rosemary and of 12.52µl for the pennyroyal and in the same two essential oils experimental conditions prevent the development of rice weevil larvae Sitophylus oryzae to 5 µl dose.

Effects of Prior Experience on Host Selection and Host Utilization by Two Populations of <I>Anisopteromalus calandrae</I> (Hymenoptera: Pteromalidae)

The effect of adult learning through an oviposition and host feeding experience was studied in two populations of Anisopteromalus calandrae (Hymenoptera: Pteromalidae), in choice and no-choice experiments in the laboratory using last instars of rice weevil, Sitophilus oryzae L., and lesser grain borer, Rhyzopertha dominica (F.), as hosts. In choice experiments, 20 wheat kernels infested by rice weevil and 20 by lesser grain borer were placed randomly in petri dish (15 by 100 mm) arenas. In no-choice experiments, 10 host-infested wheat kernels, either with rice weevils or with lesser grain borers, were mixed thoroughly in 500 g of uninfested wheat placed in a 0.945-liter glass jar (75 by 170 mm) arenas. A. calandrae females from a laboratory and field populations that were experienced with host larvae or naïve were introduced singly into each experimental arena and allowed to sting and oviposit for 24 h. An oviposition experience with rice weevil or lesser grain borer had a stronger effect on host preference in choice experiments compared with experiments with naïve wasps. Host-finding and parasitism rates were increased by prior experience with rice weevils in no-choice experiments. A. calandrae females clearly preferred rice weevil larvae for parasitization over larvae of lesser grain borer regardless of parasitoid population or prior experience. Also, A. calandrae females chose rice weevil larvae for producing female progeny and lesser grain borer for male progeny in choice experiments. The implications of the results of this study are discussed in relation to host preference and the selection of parasitoid populations for biological control programs in stored grains.

ACOUSTO-FLUIDIC DETECTION OF INSECT LARVAE IN GRAIN

DRT and USDA have entered into a Cooperative Research and Development Agreement (CRADA) to exploit the high sensitivity and signal-to-noise ratio of acousto-fluidic sensors to detect and quantify insects in grain and stored products. ARS has developed a technique for acoustically quantifying insects (including internal feeding larvae) in grain samples. ALFID (Acoustic Location Fingerprinting Insect Detector) detects individual insect sounds (chewing, moving) and cross-correlates them to determine relative time delays between sixteen sensors. This data, arranged in vectors (fingerprints) which indicate sound source locations, is compared and grouped thereby identifying the number of insects. ALFID effectiveness has been limited due to the poor SNR of conventional microphones. Initial experiments with acousto-fluidic sensors, that physically increase the sounds so that they can be detected by low cost electret microphones, have been very promising. SNR improved by 2x and insect detection probability improved by almost 3x. In three separate experiments, more than half the rice weevil larvae (Sitophilus oryzae) detected acousto-fluidically were not discerned conventionally. A 3-stage acousto-fluidic sensor (acoustic gain - 56dB, bandwidth 1 - 7kHz) driving two Tibbetts 251-01 electrets, is able to process sound levels of less than OdB SPL (ref. 0.0002, mbar). Two-week old larvae in a 1 kg grain sample have been detected at distances of over 10cm. Production cost of one sensor will be about $100, including electronics and pneumatic supply (small aquarium pump). Inadvertent export of infested grain (grain visually passed as clean) accounts for multi-million dollar annual losses. It is anticipated that the use of an acousto-fluidic ALFID system should greatly reduce these losses. Monitoring of insect infestations in silos and packaged goods will also be possible. Also, this technology may help advance infestation quantification using large arrays of multiplexed sensors coupled with ARS-developed statistical insect population estimates.

Selection of Cold Injury Treatments to Facilitate Release of the Parasitoid Anisopteromalus calandrae(Hymenoptera: Pteromalidae) Reared on the Rice Weevil (Coleoptera: Curculionidae)

The use of cold treatments to kill the rice weevil, Sitophilus oryzae (L.), before eclosion but allow the parasitoid Anisopteromalus calandrae (Howard) to complete development and eclosion was examined. Cold tolerance, crystallization temperature, and developmental stage of rice weevils were examined at 2-d intervals between 18 and 30 d after rice weevil oviposition. The median crystallization temperature dropped from 216 to 2248C over this time, and cold tolerance was lowest between day 20 and 24. Based on these data, rice weevil immatures were exposed on days 18, 19, 21, 22, 23, and 24 after oviposition fo r2ht ovarious subzero temperatures. Hosts were exposed to parasitoids for oviposition on day 20. Before parasitization, rice weevils were either frozen internally by exposure to 2258C, or were subjected to nonfreezing chilling injury by exposure to 2128C. Rice weevils exposed to cold after parasitization were subjected to chilling injury by exposure to either 212 or 2108C. Freezing rice weevil larvae before parasitization resulted in poor production of parasitoids and a sex ratio favoring males. Exposure to 2128C for 2 h, 2 or 3 d after parasitization resulted in production of parasitoids similar to unchilled controls, and a slightly higher female-to- male ratio than the controls. The production of A. calandrae was better after exposure to 2108C, but at this temperature some rice weevils eclosed. The treatment o f2ha t2128C, 3 d after parasitization gave the best parasitoid survival and ensured rice weevil mortality.

Cuticular hydrocarbons of winged and wingless morphs of the ectoparasitoid Choetospila elegans Westwood (Hymenoptera: Pteromalidae) and its host, larval lesser grain borer ( Rhyzopertha dominica) (Coleoptera: Bostrichidae)

1. 1. The cuticular hydrocarbons from winged and wingless morphs of Choetospila elegans, a larval ectoparasite of several internal-feeding stored product beetle pests, were characterized. 2. 2. All four morphs share the same cuticular hydrocarbons, with the major components being n-alkanes (C 21-C 33). 3. 3. The minor components are 3-, 11- and 13-methyl branched alkanes and Z-10-monoenes. 4. 4. Two-way analysis of variance (sex and wing morph) shows that males and females have the same profiles, whereas four components showed significant differences between wingtype morphs. 5. 5. Only one of these four hydrocarbons (n-C 31) was a major component. 6. 6. The cuticular hydrocarbons of larvae of the lesser grain borer, Rhyzopertha dominica, were also characterized. 7. 7. Although the beetles' major components were the same n-alkanes as those found on the adult parasites, their minor components were different. 8. 8. Thus, the beetle larvae have no alkenes, but instead have 3-, 11-, 13- and 15-methylbranched alkanes, as well as a series of 11,15-dimethylalkanes. 9. 9. A cuticular hydrocarbon profile obtained on a population of C. elegans winged females that had been reared on rice weevil larvae was nearly identical to that from winged females reared on the lesser grain borer larvae.

Growth Responses of Larvae of the Rice Weevil, Maize Weevil, and Granary Weevil on a Meridic Diet12

Growth and development of larvae of the rice weevil, Sitophilus oryzae (L.), and the maize weevil, S. zeamais Motschulsky, reared on a meridic diet at 32°C and 65% RH, were compared. Although the mean larval weight of S. zeamais after 11 days on the diet was 4.36±1.07 mg compared with 3.01±0.59 mg for S. oryzae , the developmental times of the different life stages were nearly identical for both species. Adult emergence (eclosion) for both species began after 17 days and was complete after 23 days, with 93.5% of the S. oryzae larvae and 80% of the S. zeamais larvae emerging as adults. The larval growth rates of S. oryzae and the granary weevil, S. granaries (L.), also were directly compared. Not only were the rice weevil larvae more uniform in their developmental times, but the larvae reached maturity and pupated an average of 8.5 days earlier than did the larvae of S. granaries . The utility of using these rearing procedures to assess the effects of varietal nutritional differences among cereals upon larval development and survival is discussed.

Laboratory Tests of Five New Insecticides as Protectants for Stored Rough Rice

Candidate insecticides Bromodan (5-(bromomethyl)-1, 2, 3, 4, 7, 7-hexachloro-2-norbornene), Bay 39007 ( o -isopropoxyphenyl methylcarbamate), Amer. Cyan. CL 47300 ( O, O -dimethyl O -4-nitro- m -tolyl phosphorothioate), Ciodrin® ( alpha -methylbenzyl 3-hydroxycrotonate dimethyl phosphate), and Shell SD 7438 S, S' -benzylidene bis ( O, O -dimethyl phosphorodithioate) were tested as protectants for rough rice. Malathion was included as a standard, since it is known to be an effective, long-term protectants for rough rice during storage. Test insects were about rice weevils, Sitophilus oryzae (L.); confused flour beetles, Tribolium confusum Jacquelin duVal; lesser grain borers, Rhyzopertha dominica (F.); and rice weevil larvae. The most generally effective compound was CL 47300. Bromodan produced the best control of lesser grain borers hut was ineffective against the other species.

Effects of Number of Test Insects, Exposure Period, and Posttreatment Interval on Reliability of Fumigant Bioassays11

Studies were designed to determine the reproducibility of re- sults from standardized laboratory fumigation tests using an 80:20 (CCI4:CS2 by vol.) fumigant in empty 20-liter bottles at 80° F. The test insects were adults of rice weevil ( Sitophilus orlyza (L.)), confused flour beetle ( Tribolium confusum Duv.), and saw-toothed grain beetle ( Oryzaephilus surinamensis (L.)) and three age groups of immature rice weevils. Analysis and evaluations showed that (1) the optimum number of adult insects used in each test cage was 50; (2) rice weevil and confused flour beetle should be held at least 10 days and sawtoothed grain beetle 15 days after fumigation for final mortality counts; (3) the descending order of resistance to the fumigant was rice weevil pupae, eggs, and larvae, and adult saw-toothed grain beetles, confused flour beetles, and rice weevils, and (4) variation in results was unpredictable although variations were greatest with rice weevil adults and smallest with rice weevil larvae. Results of parallel experiments conducted on different days were highly variable in some instances, but replicates within a given day's tests were reasonably consistent. Adult insects demonstrated greater variation following longer exposures to the fumigant than following shorter exposures. conducted weevils responded erratically following the shorter exposures but varied least of all groups in the 48-hour exposures. Sub lethal treatments of immature rice weevils retarded their rate of development. LC values with their respective confidence intervals were determined. The observed LC50 and LC90 values associated with 24- hour exposures were 290 and 370 µM./1. (micromoles per liter) for confused flour beetle adults, 165 and 220 µM./1.for rice weevil adults, 125 and 500 µM1./1. for rice weevil eggs and young larvae, 155 and 345 µM./1. for young and middle-aged rice weevil larvae and 375 and 865 µM1./1.for older rice weevil larvae and pupae. I.C values for 4- and 8-hour exposures were greater, and those for 48-hour exposures were smaller, than the 24-hour I.C values.