The compound eyes of a male red palm weevil, Rhynchophorus ferrugineus (Olivier), were investigated using scanning techniques, specifically, the ommatidium in the dorsal rim area was studied by light and electron microscopy. Each eye contained 3000-3500 mostly hexagonal facets. No ocelli, corneal nipples or interommatidial hairs were found. The eye was of the acone and apposition types, with 8 retinular cells per ommatidium (two central, six peripherals).The peripheral distal and proximal rhabdome were composed of six separated rhabdomeres, with the separation between them increased by interretinular spaces. The central distal rhabdom consists ofr7, while the central proximal rhabdomeres was fused by R7 and R8. The microvilli of the peripheral distal rhabdomeres R2, R3, and, the central proximal R7, R8 were arranged in a three-dimensional pattern, where as distal R4 was warped around itself. The distal R7 and the proximal R1-R6 were possessed microvilli oriented in such away as to permit e-vector discrimination. The difference between the central and peripheral rhabdomeres in the two rhabdom regions. With regard to the microvillar arrangement implied the occurrence of the rhabdomeric twist. It was encountered only at the distal region, where the rhabdomeric organization displayed an effective strategy to improve absolute sensitivity, at the expense of the polarization of sensitivity, to overcome the particular problem of vision in dim habitats. A possible function in the perception of host related visual cues is proposed and discussed in relation to the plausible roles of the dorsal rim area in host location by male weevils.
The Crude Extract and powder of Lepidium sativum Linn. seeds were evaluated for a toxicity effect on 5 th instar larvae of the Trogoderma granarium beetle by vapor and diet incorporation methods, respectively, as well as the repellent indicators of the powder at concentrations of 2, 0.9, 0.5, and 0.1% (w/w); the toxicity assay of essential oil was evaluated at 20, 15, 10, and 5 µl/L air. The results show that a variety of 5 th larvae responses proved the effectiveness, where the essential oil vapors showed a high fumigate toxicity at 28.64 µl/L air, where the LC50 was identified after 72 hours of exposure. Additionally, the powder showed a toxicity effect at the concentrations of 2, 0.9 and 0.5% (w/w), which caused 100 and 96% mortality, respectively, and the LC50 was identified at 0.26% after 10 days of treatment. The exhibited repellent percentages of the powder were weak and at the same time had high acceptance and larval attractivity to the wheat grains treated. The attractive percentage was determined at -53.3% and -66.6% at the lowest and highest applied concentrations of 0.1% and 2% after 72 hours of exposure. The presence of the inverse relationship between the attractive and toxicity properties of the same material (L. sativum seeds) is a promising sign to the safe modeling of toxic baits, which attract and then kill larvae.
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