Insects as food: why the western attitude is important.

The traditional use of insects as food continues to be widespread in tropical and subtropical countries and to provide significant nutritional, economic and ecological benefits for rural communities. Westerners should become more aware of the fact that their bias against insects as food has an adverse impact, resulting in a gradual reduction in the use of insects without replacement of lost nutrition and other benefits.

La Crosse viremias in white-tailed deer and chipmunks exposed by injection or mosquito bite.

To further understand the role of wild mammals in the maintenance of La Crosse virus (LACV) in nature, we investigated the effects of inoculation method and virus source on the duration and amplitude of LACV viremia in vertebrate hosts. Earlier work suggested that deer are not sufficiently susceptible to LACV to play an important role in its maintenance. We re-evaluated the susceptibility of deer since subsequent studies showed that they constitute 65% of Aedes triseriatus blood meals, and thus would be exposed frequently to the virus. In our study, deer developed higher and longer viremia following exposure to LACV by infected Ae. triseriatus than those previously reported by inoculation with needle and syringe. However, susceptible Ae. triseriatus that fed on these viremic animals did not become infected. Because a large number of uninfected mosquitoes can feed upon a viremic deer in nature, we believe that deer should not be disregarded completely as a possible amplifier in the LACV transmission cycle. We also infected chipmunks to determine if there were significant differences in viremia response from mosquito delivery of virus to the chipmunk host, compared with artificial exposure by injection. Chipmunks exposed to infected mosquitoes had higher and longer viremias than the ones produced by intramuscular injection of an LACV suspension. These findings show the importance of using LACV infected mosquitoes for transmission experiments in mammals.

Potential use of scrap expanded polystyrene beads for the control of Aedes triseriatus.

The potential use of expanded polystyrene (EPS) beads for control of Aedes triseriatus was tested in the laboratory and the field. Laboratory studies showed that beads present in amounts which persisted throughout a season significantly reduced the emergence of Ae. triseriatus adults by preventing normal eclosion from the pupae. In the field, tree holes containing EPS beads had significantly fewer larvae present than untreated controls. These field data suggest that EPS beads may mechanically prevent oviposition by mosquitoes.

Residual toxicity of four insecticides to Aedes triseriatus in scrap tires.

Four insecticides were tested for residual activity to Aedes triseriatus in scrap tires. Abate (temephos) granules applied at 10 ppm (AI) resulted in 100% mortality of 4th instar larvae for more than one year. The other insecticides caused no mortality within 4 wk after application.

A field evaluation of two suggested Aedes triseriatus oviposition attractants.

Two reported oviposition attractants for Aedes triseriatus, fish oil emulsion and water of high optical density, were evaluated in ovitraps in the field. Solutions of fish oil emulsion at 1% repelled ovipositing mosquitoes, whereas water containing vegetable dye increased oviposition up to 4-fold over control traps. Laboratory bioassays with fish oil emulsion at both 1 and 5% confirmed the field results.

Spatial distribution of Aedes triseriatus eggs in a site endemic for La Crosse encephalitis virus.

Egg laying behavior in Aedes triseriatus was studied in an oak woodlot endemic for La Crosse encephalitis virus in southwestern Wisconsin. Daily counts from oviposition traps allowed the calculation of spatial distribution parameters for eggs during 1988. Egg distribution along an ellipsoidal transect of 25 traps was clumped with some traps being more attractive to ovipositing female Ae. triseriatus than others. Females were estimated to deposit a mean of 31 +/- 9.8 eggs per oviposition.

Use of a four-parameter logistic model to evaluate the quality of the protein from three insect species when fed to rats.

The quality of three insect protein sources [Mormon cricket meal (MCM), house cricket meal (HCM) and Eastern tent caterpillar meal (TCM)] was evaluated relative to that of lactalbumin (LA) and soy protein (SP) by using both amino acid analysis and a rat bioassay. The amino acid pattern of the three insect meals indicated that methionine should be the first limiting amino acid for growing rats. In the rat bioassay, weanling Sprague-Dawley rats were fed graded levels of the five proteins in purified diets and the response (weight or nitrogen gain) evaluated as a function of nitrogen intake. The individual nitrogen intake-animal response results could be described by a series of curves using a four-parameter logistic model. The use of parameter sharing permitted the full range of responses to be described so that statistical differences between the dose-response curves could be identified. When used for either weight maintenance, nitrogen equilibrium, maximum weight gain or maximum nitrogen retention, the five protein sources could be ranked in the following order: LA greater than HCM greater than MCM = SP greater than TCM. Relative to lactalbumin, the value of all four protein sources decreased with increasing nitrogen intake. The low values obtained for TCM may have been related to factors other than protein quality. The results of this study indicate that some insect proteins are equivalent or superior to soy protein as a source of amino acids for growing rats.

California serogroup virus infections in Wisconsin domestic animals.

A serologic survey and experimental virus transmission studies were done to assess the role of domestic animals as amplifier hosts of La Crosse (LACV) and Jamestown Canyon (JCV) viruses. Serum from 319 cows, 88 dogs, 122 equines, 47 swine, 10 goats, and 4 cats were tested for neutralizing antibody to LACV, JCV, trivittatus (TVTV), and snowshoe hare (SSHV) viruses. Antibody prevalences of LACV, TVTV, and SSHV were less than 10% in all species. Antibody to JCV was detected in all species except cats. Prevalence ranged from 10% in goats and swine to 29% in dogs. No age-associated trends in JCV prevalence were noted. Two of 6 adult dogs, and 2 of 4 pigs inoculated with 6.3-6.5 log10 suckling mouse intracerebral 50% lethal doses (SMICLD50) of LACV developed viremias ranging of less than 1.0-2.9 log10 SMICLD50/ml 1-3 days after inoculation. Of 4 puppies inoculated with LACV, 3 developed fatal infections. Viremias were not detected in 4 cows, 4 ponies, 7 cats, or 6 sheep. Two cats fed LACV infected suckling mice shed virus from the oropharynx for 1 day each. All animals except 1 cow, 1 cat, and 1 sheep had greater than or equal to 4-fold rise in antibody titers. Five additional dogs fed upon by LACV-infected Aedes triseriatus mosquitoes did not develop viremias or antibody and uninfected Ae. triseriatus engorging on the dogs 1-5 days after feeding by infected mosquitoes failed to become infected. Five ponies, 6 calves, 2 ewes, 6 dogs, and 5 piglets were inoculated with 3.6-7.3 log10 SMICLD50 of JCV. None developed detectable viremias, although greater than or equal to 4-fold rises in antibody titers developed in 60% of the ponies, 17% of the calves, 50% of the dogs, and 1 of 2 ewes. None of the pigs developed corresponding rises in antibody titers. We conclude that juvenile and adult animals of the species tested are not efficient amplifier hosts of LACV or JCV, but may be useful sentinels of local virus transmission.

Adult body size and survivorship in a field population of Aedes triseriatus.

Aedes triseriatus pupae, host-seeking, and ovipositing females were collected at a southern Wisconsin site endemic for La Crosse encephalitis virus. The host-seeking and ovipositing females were age-graded by the Detinova and Polovodova techniques, respectively. Wing lengths were determined for all mosquitoes. Wing lengths of the mosquitoes collected as pupae were predicted from pupal weight by a simple regression equation. There was significant seasonal variation in body size of adult females, but no strong evidence that increased size was advantageous to survival. It is concluded therefore that the potential length of infective life is not affected by the size of the adult female.

Use of simultaneous curve fitting and a four-parameter logistic model to evaluate the nutritional quality of protein sources at growth rates of rats from maintenance to maximum gain.

A four-parameter logistic model was used to describe the dose-response relationship of rats fed diets containing 12 levels of casein, peanut meal or wheat gluten. The model was capable of accurately describing the entire response curve of rats fed diets containing each of the three protein sources. Incorporation of a technique known as parameter sharing into the curve-fitting process facilitated convergence of the parameter estimates for b (the response of rats fed a protein-free diet) and Rmax (maximum response) for all curves when compared with the values observed experimentally. Parameter sharing also provided a method by which the curves could be differentiated on a statistical basis. These data indicate that the relative value of a protein source is dependent on the concentration of the protein in the diet. The application of nonlinear models combined with parameter sharing provides a technique by which protein values can be evaluated at levels of animal response from maintenance to maximum growth.

Use of a four-parameter logistic model to evaluate the protein quality of mixtures of Mormon cricket meal and corn gluten meal in rats.

Weanling Sprague-Dawley rats were fed diets containing corn gluten meal (CGM), Mormon cricket meal (MCM), MCM supplemented with methionine (MCM + Met) or CGM-MCM mixtures as the sole source of dietary protein in purified diets. Animal response (weight or nitrogen gain) was analyzed as a function of nitrogen intake and described by a series of curves using a four-parameter logistic model. Parameter sharing was used to differentiate statistically between the response curves. When used for maximum nitrogen retention the quality of the protein sources could be ranked as follows: MCM + Met greater than 40 CGM-60 MCM greater than 50 CGM-50 MCM greater than 60 CGM-40 MCM greater than MCM greater than CGM. When used for maximum weight gain the ranking was as follows: MCM + Met greater than 40 CGM-60 MCM greater than 50 CGM-50 MCM greater than 60 CGM-40 MCM greater than MCM greater than CGM. The rankings of the protein sources when used for weight maintenance or nitrogen equilibrium were similar to those seen for maximum weight or nitrogen gain except for the ranking of MCM, which changed from fifth to first. These results show MCM to be a good quality protein source and that methionine is the first limiting amino acid when used for growth but not for maintenance. The shape of the response curves was dependent upon the response criteria as well as the source of dietary protein. The factors that may affect the shape of the dose-response curves and the application of nonlinear models toward animal feeding programs are discussed.

Aedes triseriatus and La Crosse virus: similar venereal infection rates in females given the first bloodmeal immediately before mating or several days after mating.

Venereal infection rates of Aedes triseriatus females mated to males transovarially infected with La Crosse virus were determined in 6 cage-mating trials. In trials 1-4, venereal infection rates averaged 46% and 45% in F2 females bloodfed 6-8 hr before and 7 days after exposure, respectively, to transovarially-infected males. These rates were similar to rates previously reported only in mosquitoes receiving a bloodmeal 6-8 days prior to mating. Lower rates (24%-31%) were obtained using F4 and F7 generation mosquitoes in trials 5B and 6. In most trials, oral and transovarial transmission rates by venereally infected females were less than 25%. In trial 5B, however, the transovarial transmission rates reached 60% and 94% in the second and third ovarian cycles, respectively, with filial infection rates of 46% and 65%, respectively. The oral transmission rate in this trial reached 38% after 32 days. LAC virus was not detected in first ovarian cycle progeny. It is concluded that higher venereal infection rates must be found and/or first ovarian cycle progeny shown to become infected, before venereal transmission can be considered to make more than a modest contribution to offsetting the erosion of virus prevalence during TO transmission.

Changing patterns in mosquito-borne arboviruses.

Research leading to the current state of knowledge on the epidemiology of La Crosse virus (LACV), Jamestown Canyon virus (JCV) and dengue (DEN) viruses is summarized in relation to the generally recognized criteria for incriminating vectors. The importance of vector biology and local ecological conditions is emphasized as is the necessity of a good balance between laboratory and field-based studies. The influence of human activity in shaping the epidemiological patterns of all three of these arboviruses is readily apparent.

Oral infection and transmission of La Crosse virus by an enzootic strain of Aedes triseriatus feeding on chipmunks with a range of viremia levels.

The susceptibility of Aedes triseriatus to oral infection with La Crosse (LAC) virus resulting from feeding on chipmunks with viremia titers of 0.6 to 4.6 log10SMICLD50/0.025 ml was determined. Results indicated that viremia titers must exceed 3.2 log10SMICLD50/0.025 ml before a significant proportion (greater than or equal to 50%) of mosquitoes are infected and capable of transmitting LAC virus. Mosquitoes which fed on chipmunk blood-LAC virus mixtures through a membrane feeder had significantly lower infection rates at virus titers of 1.8 to 4.4 log10SMICLD50/0.025 ml and transmission was also significantly reduced. Application of these data to LAC viremia titers measured in chipmunks in an earlier study indicate that viremias sufficiently high to ensure transmission by the mosquitoes becoming orally infected average only about 1 day per infective bite delivered to the susceptible portion of the amplifier population. Oral infection and transmission rates were also determined for Ae. triseriatus feeding on chipmunk blood containing LAC virus neutralizing (N) antibodies and for Ae. triseriatus feeding on deer blood containing Jamestown Canyon (JC) virus N antibodies. Infection rates were similar to those observed in mosquitoes imbibing blood free of N antibody at the virus titers tested, but, oral transmission was reduced in females feeding on chipmunk blood-LAC virus mixtures containing LAC N antibodies and there was no transmission by females feeding on deer blood-LAC virus mixtures containing JC N antibodies. These data suggest that high LAC antibody prevalences in chipmunk populations and high LAC or JC antibody prevalences in deer populations may be antagonistic to horizontal LAC virus transmission.