Effects of permethrin on the salivary glands and neuroendocrine organs of unfed female Hyalomma (Hyalomma) dromedarii (Ixodoidea: Ixodidae).

Permethrin-impregnated fabric has been shown to be an effective repellent against various tick species. However, some tick species are not repelled by this chemical. In Hyalomma dromedarii (Koch), permethrin exposure is reported to actually enhance the tick's attachment behavior. This study evaluated the histological effects of permethrin exposure on the salivary glands and neuroendocrine organs of unfed, virgin H. dromedarii ticks of uniform age. Three fabric treatments consisting of unwashed-untreated (control), washed after treatment (0.125 mg [AI] / cm2) and unwashed-treated were used after 5- and 10-min exposure times for unfed, unmated females. For all of the organs examined, the cellular structure of treated ticks differed from controls as evidenced by increases in cellular activity, as well as significant increases in the size of the cells of the organs under study (P < 0.05). These data conclusively demonstrate that an unexpected enhanced attachment response observed in this tick species after permethrin exposure is the direct result of increased neurosecretory and salivary gland activity induced by that exposure.

Induction of some digestive enzymes in the midgut of the sandfly Phlebotomus langeroni after sugar and blood meals.

Changes associated with blood and sugar meal digestion in the sandfly, Phlebotomus langeroni were characterized. Different types of sugars: sucrose, glucose, melibiose, cellobiose, lactose, starch, fig fruits, honey dew and a mixture of sucrose and sugar sources were used for the sandfly feeding. Activities of glycosidases and proteases in the sandfly guts after blood and sugar meals were determined using the endpoint method. The results showed that glycosidases (alpha-glycosidase, beta-glycosidase, alpha-galactosidase, and beta-galactosidase) are present in the sandfly midguts. No activities of the glycosidases (alpha-mannosidase and alpha-amylase) were detected in the sandfly gut. Proteases: trypsin and aminopeptidase showed activities in the sandfly midguts. It is concluded that the midgut glycosidase may play an important role in the vector-parasite interaction. Trypsin and aminopeptidase induction after a blood meal is controlled by a secretogogue mechanism which indirectly influences the outcome of the Leishmania parasite infection.

Contact toxicity of permethrin-impregnated fabric to Hyalomma anatolicum excavatum (Acari: Ixodidae): effects of laundering and exposure and recovery times.

A previous study that documented enhanced host attachment by the camel ticks Hyalomma dromedarii Koch after permethrin exposure prompted a similar investigation of permethrin effects in H. anatolicum excavatum Koch, an Old World hardbacked tick suspected of vectoring human pathogens. Contact toxicity tests were conducted with laboratory-colonized male and female H. a. excavatum of the same age exposed for periods of 5, 10, 30, and 60 min to each of 5 fabric treatments: unwashed/untreated; unwashed and treated; and treated fabric given 1, 2, or 3 laundry cycles of warm-water detergent machine washing, followed by hot-air drying. Fabric was tropical weight 100% cotton military uniform. Treated fabric was impregnated with permethrin at 0.125 mg (AI)/cm2. Contact toxicity was measured immediately after and 24 h after fabric contact as proportion of ticks that attached mouthparts to the skin of a host (rabbit) within a 60-min quest period and time lapse (minutes) between contact with the host and attachment. Attachment response immediately after permethrin contact was exposure time- and wash-dependent in both sexes. Proportion of attaching ticks and times to attachment were comparable in controls and in groups exposed to all permethrin-treated fabrics for 5 or 10 min. Contact periods of 30 and 60 min with 0-wash/treated or 1-wash and treated fabric significantly reduced the frequency of attachment and significantly prolonged mean times to attachment. Compared with low levels of attachment response observed immediately after fabric contact, recovery of attachment response was observed 24 h after exposure in these wash/treatment groups, but inhibition was still evident. Permethrin-induced intoxication was more pronounced in males than females. Mortality 24 h after exposure was only significant among females exposed to 0-wash/treated fabric for 60 min. There was no evidence of permethrin-mediated stimulation of the attachment response in H. a. excavatum.

Contact toxicity of permethrin-impregnated military uniforms to Culex pipiens (Diptera:Culicidae) and Phlebotomus papatasi (Diptera: Psychodidae): effects of laundering and time of exposure.

The effects of laundering and time of exposure on the insecticidal activity of military uniform fabric impregnated with permethrin at 0.125 mg active ingredient (AI)/cm2 are reported from susceptibility tests with laboratory-reared mosquitoes, Culex pipiens, and sand flies, Phlebotomus papatasi. Knockdown/mortality resulting from exposure of groups of female insects for periods of 1, 3, 5, 7, and 10 min was recorded and compared among 5 different treatment/wash groups (untreated/unwashed, treated/unwashed, treated/1-wash, treated/2-wash, treated/3-wash). Laundering was by machine washing with detergent and warm water followed by hot-air machine drying. Post-exposure assessments at intervals from 0 to 60 min and at 24 h showed that knockdown for each exposure time and wash group was initially low but increased steadily during the first hour post-exposure. Sand flies were less sensitive than mosquitoes to knockdown during the first 60 min after contact with treated/unwashed fabric; however, 24-h mortality rates for sand flies were higher as compared with mosquitoes. The permethrin remaining after a 3rd wash had little knockdown effect on mosquitoes but was toxic to sand flies at each of the 5 exposure times. Significant reductions in the knockdown effectiveness of permethrin-treated fabric to mosquitoes and sand flies was associated with single and repeated washings of the fabric.

Stimulation of attachment in a camel tick, Hyalomma dromedarii (Acari: Ixodidae): the unintended result of sublethal exposure to permethrin-impregnated fabric.

The susceptibility of a camel tick, Hyalomma dromedarii (Koch), to permethrin-impregnated military uniform fabric was studied to determine the effects of laundering and contact time. Separate contact toxicity tests were conducted with laboratory-colonized male and female ticks of uniform age. Unfed, unmated ticks were exposed for periods of 5, 10, 30, and 60 min to each of five fabrics: unwashed-untreated, unwashed-treated, and 1, 2, or 3 times washed after treatment (1-, 2-, 3-wash-treated). Treated fabric was impregnated with permethrin at 0.125 mg (AI)/cm2. Laundering was by machine washing with detergent followed by hot air machine drying. Intoxication immediately after exposure was assessed by activity response: the proportion of ticks attaching to a host (rabbit) within 60 min and the average time elapsed between contact and insertion of mouthparts. Unexpectedly, permethrin exposure activated an attachment response in both sexes. At all contact times, and in each wash-treated group, a greater proportion of ticks attached, and did so more rapidly, than in controls. Mortality assessment 24 h after exposure showed that females were more tolerant than males and experienced light mortality even after 60 min of contact. Both natural and acquired factors may account for permethrin tolerance in this species. Consistent with pyrethroid mode of action and pheromone function in ticks, it is hypothesized that sublethal levels of permethrin may act on H. dromedarii to induce premature or excess release of a neurosecretory substance that elicits attachment.