Eli Shaaya

Plant oils as fumigants and contact insecticides for the control of stored-product insects

The fumigant toxicity of a large number of essential oils extracted from various spices and herb plants was assessed against several major stored-product insects. Tribolium castaneum (Herbst) was found to be the most resistant, compared with Sitophilus oryzae (L.), Rhyzopertha dominica (F.) and Oryzaephilus surinamensis (L.), to most essential oils tested. With the highly active Labiatae sp. oil ZP51, a concentration of 1.4–4.5 μl/l air and exposure time of 24 h was enough to obtain 90% kill of all the insects in space tests. In columns 70% filled with wheat, a concentration of 50 μl/1 and 7 d exposure were needed to obtain 94–100% kill of the insects. The biological activity of a number of edible oils, when applied as contact insecticides, was assessed in field studies. Edible oils are potential control agents against Callosobruchus maculatus (F.) and, to a lesser extent against Sitophilus zeamais Motsch., S. oryzae and Sitotroga cerealella (Oliv.). These materials could be very useful on the farm level in developing countries. Plant oils can play an important role in stored-grain protection and reduce the need for, and risks associated with, the use of insecticides.

Biological activity of two juvenoids and two ecdysteroids against three stored product insects.

The insecticidal activity of juvenile hormone agonists methoprene and pyriproxyfen, and the ecdysone agonists RH-5849 and tebufenozide was evaluated against susceptible and actellic-resistant strains of Tribolium castaneum and susceptible strains of Rhyzopertha dominica and Sitophilus oryzae. Concentrations ranging from 0.1 to 20 ppm of the analogues were mixed in the food medium to which the tested insects were exposed. The results showed that all these compounds could affect the development of the tested species to differing extents but had no effect on the mortality of parental adults. The two JH analogues did not prolong the life span of R. dominica and S. oryzae, but very greatly extended that of T. castaneum. The extension led to the production of giant larvae and failure to pupate. Actellic-resistant strain of T. castaneum showed some cross-resistance to methoprene and pyriproxyfen, but not to RH-5849 and tebufenozide. Pyriproxyfen was the most effective compound among the four IGRs; a concentration of 0.1 ppm could completely inhibit the F(1) adult occurrence of both S- and R-strains of T. castaneum and its LC(90)s for controlling R. dominica and S. oryzae were 0.1 and 1.2 ppm, respectively. Methoprene was highly effective against R. dominica, but less active on S. oryzae. RH-5849 could achieve almost complete control of F(1) adults of T. castaneum and R. dominica at 10 ppm, but was less potent on S. oryzae. Tebufenozide appeared to be much less active on these three species compared with the other three compounds. The percentage reductions of F(1) adults for S- and R-strains of T. castaneum at a concentration of 20 ppm were 80 and 99%, respectively.

Immuno-Fluorescent analysis of follicular growth and development in whole ovaries of the Indianmeal moth

The differentiation and growth of ovaries was analyzed using immuno‐fluorescence microscopy and then correlated with the changes in the external morphology of female pupae during metamorphosis of the Indianmeal moth, Plodia interpunctella (Hübner). Fourteen developmental points coincident with a daily change in the light:dark cycle were chosen for observation to describe the progress of cuticular, ovarian, and follicular development during metamorphosis. Follicular structure was examined in whole mounts of ovaries using an immuno‐fluorescent labelling technique. The growth of oocytes and nurse cell cap in terminal follicles was measured throughout ovarian development. A rapid increase in the relative size of the nurse cells began during the fourth scotophase and continued until the beginning of the sixth scotophase. Following the sixth scotophase, the relative size of the nurse cells decreased until they disintegrated prior to choriogenesis. Oocytes began to grow rapidly during the fifth scotophase, coincident with the initiation of vitellogenesis, and continued to grow until choriogenesis was initiated just after adult eclosion. The rate of follicular growth was related to the position of the follicle in the ovariole; the closer to the terminal position, the greater the rate of growth. Thus, at adult eclosion, each ovariole contained a linear array of follicles in progressive stages of development with the terminal follicles ready to begin choriogenesis.

Declining ecdysteroid levels are temporally correlated with the initiation of vitellogenesis during pharate adult development in the Indianmeal moth, Plodia interpunctella

Photo-synchronized pupae were used to determine the titer of ecdysteroids during the pupal and pharate adult stages of the Indianmeal moth, Plodia interpunctella (Hiibner). For female pupae that were kept in a 16h 1ight:S h dark (longday) photocycle, there was one major peak of ecdysteroids. The ecdysteroids reached a maximum of 2000-2500 pg/mg wet wt between 28-36 h after pupation. The ecdysteroids declined to 400 pglmg wet wt by 68 h after pupation. For pupae that were kept in continuous darkwss, the ecdysteroid peak became broader with a maximum at 24 h (3130 pg/mg wet wt). The composition of ecdysteroids at various times during pharate adult development was determined usiug gas chromatographass spectrometry with selected ion monitoring (GC-MS (S1M)I. Eedysone was the major component (93%) in samples taken 28 h after pupation, at the maximum of the pupal peak. Thus, high levels of ecdysoue are correlated with the beginning of adult ovarian development. As pharate development progressed, the proportion of 20-hydroxyecdysow increased so that by 100 h after pupation 20-hydroxyecdysone was the only ecdysteroid detected. Previously, the initiation of vitellogenesis was determined to begin between % and 100 h after pupation. In conjuction with previous work, these findings demonstrate that the ecdysteroid titers decline before viteUogenesis is initiated and egg maturation can be completed. Ecdysteroids Vitellogenesis Metamorphosis Radioimrnunoassay GC-MS quantification

Yolk sphere formation is initiated in oocytes before development of patency in follicles of the moth,Plodia interpunctella

We describe a provitellogenic stage, a previously unrecognized stage of follicle development in moths, and show that oocytes begin yolk sphere formation prior to the development of patency by the follicular epithelium. The vitellogenic activities of follicles from pharate adult femalePlodia interpunctella (Hübner) were determined by visualizing the subunits of vitellin (YP1 and YP3) and the follicular epithelium yolk protein (YP2 and YP4) using monospecific antisera to each subunit to immunolabel whole-mounted ovaries or ultrathin sections. At 92 h after pupation, yolk spheres that contained only YP2 began to proliferate in the oocytes. The inter-follicular epithelial cell spaces were closed at 92 h making vitellogenin inaccessible to the oocyte, and consequently, the vitellin subunits were not observed in the yolk spheres. YP2 uptake most likely occurred across the brush border from the follicular epithelial cells to the oocyte at this time. At 105 h, the inter-follicular epithelial cell spaces appeared closed yet trace amounts of labeling for vitellin were observed in the spaces and also in the yolk spheres along with YP2. Equivalent labeling for all four YPs in yolk spheres was finally observed at 112 h after pupation when the follicular epithelium had become patent. These data indicate that the provitellogenic stage is an extended transition period between the previtellogenic and vitellogenic stages that lasts for approximately 13 h, and it is marked at the beginning by YP2 yolk sphere formation in the oocyte and at the end by patency in the follicular epithelium.

The lethal effects of three insect juvenile hormone analogues on the developmental stages of Ephestia cautella (Wlk.) (Lepidoptera: Phycitidae)☆

Abstract The juvenile hormone analogue methoprene (ZR 515) was found to interfere with normal development of Ephestia cautella in a manner dependent on dose and age. This compound was found to cause the formation of non-viable 1st instar larvae when it was given to young eggs prior to the stage of blastokinesis, but it was less effective against older eggs. Methoprene inhibited metamorphosis and produced supernumerary giant larvae when it was given to larvae 5 days prior to pupation or younger. However, when given 1–3 days before pupation, it did not prevent pupation but did prevent adult emergence. Young pupae within 1 day of pupation were also found to be very sensitive to the compound. It appears that a small ecdysteroid peak detected 5 days prior to pupation might be responsible for the transition from inhibition of pupation to defective metamorphosis. Methoprene (ZR 515) and hydroprene (ZR 512) were more effective in prolonging the larval period than kinoprene (ZR 777), which, however, was the most effective against Ephestia larvae.

Sex pheromone of Dermestes maculatus De Geer (Coleoptera, Dermestidae)

Abstract Virgin males of Dermestes maculatus were attracted to males of the same species by a pheromone which could be extracted with hexane from both males and females. Females were unresponsive to their own sex and showed only a slight response to males. Faeces extracts of both sexes attract males but not females.

The Potential of Biofumigants as Alternatives to Methyl Bromide for the Control of Pest Infestation in Grain and Dry Food Products

Fumigation is still one of the most effective methods for the protection of stored grain and dry food from insect infestations. Phosphine and methyl bromide are the most widely used fumigants for the control of stored-product insects. Phosphine is mainly used today, but there are repeated reports that a number of storage pests have developed resistance to this fumigant. Methyl bromide has been identified as a contributor to ozone depletion by the United Nations World Meteorological Organization in 1995 and, thus, was phased out in most developed countries. Thus, there is an urgent need to develop alternatives with the potential to replace these fumigants.

Advanced Methods for Controlling Insect Pests in Dry Food

Methyl bromide (MB) and Phosphine were the most widely used fumigants for controlling insect pest infestation in grain, dry food products and quarantine insects in cut flowers. Lately, the phase out of MB in developed countries, Phosphine became a major fumigant for the control of stored product insects. However, limitations, such as low temperature and relatively long exposure time, limit its use. This situation made it urgent to search for new techniques to improve the fumigation with Phosphine and for alternative environmentally sound and cost effective control agents. In order to improve Phosphine application a special device, containing a heater and a ventilator, called “Speedbox”, was evaluated. In addition, the potential use of essential oils as botanical fumigants obtained from aromatic plants, and the use of Diatomaceous Earth as grain protectant were evaluated against major stored product insects.

Coarse and nano emulsions for effective delivery of the natural pest control agent pulegone for stored grain protection: Coarse and nano emulsions of pulegone for insecticide use

BACKGROUND One of the most significant contributors to the global food crisis is grain loss during storage, mainly caused by pest insects. Currently, there are two main methods used for insect pest control: fumigation and grain protection using contact insecticides. As some chemical insecticides can harm humans and the environment, there is a global tendency to reduce their use by finding alternative eco-friendly approaches. RESULTS In this study, the natural pest-managing agent pulegone was encapsulated into coarse and nano emulsions. The emulsions were characterized using spectroscopic and microscopic methods and their stability and pulegone release ability were examined. The insecticidal activity of the prepared formulations against two stored product insects, rice weevil (Sitophilus oryzae L.) and red flour beetle (Tribolium castaneum Herbst), was demonstrated. The nano emulsion-based formulation offered significant advantages and provided powerful bioactivity, with high (> 90%) mortality rates for as long as 5 weeks for both insects, whereas coarse emulsions showed high efficacy for only 1 week. CONCLUSION The developed pulegone-based nano emulsions could serve as a model for an effective alternative method for pest control. Although pulegone is from a natural source, toxicological studies should be performed before the widespread application of pulegone or pulegone-containing essential oils to dry food products.