Effects of nutrition and density in Culex pipiens.

Mosquito larvae face numerous biotic and abiotic challenges that affect their development and survivorship, as well as adult fitness. We conducted two experiments under semi-natural conditions to evaluate the effects of intraspecific competition, nutrient limitation and sub-lethal doses of malathion on individual life history traits in adult Culex pipiens (Diptera: Culicidae). In the first experiment, larvae of Cx. pipiens were reared at different intraspecific densities and exposed to sub-lethal doses of malathion. In the second experiment, different intraspecific densities of Cx. pipiens larvae were reared under conditions of low or high larval nutrients, and subsequent adults were fed on either water or 10% sucrose solution. Malathion treatment had relatively minor effects compared with density, which had significant negative effects on development rate, survivorship to adulthood, body size (wing length) and longevity. As larval density increased, a sex ratio distortion in survivorship to adulthood emerged, in which a bias towards males was apparent. Nutrient-rich larval environments alleviated, in part, the effects of increasing density and extended the lifespan of mosquitoes fed on water and 10% sucrose. Density-dependent alterations in adult longevity attributable to the larval environment are complex and show contrasting results depending on interactions with other environmental factors. This study suggests that larval resource availability and competition influence Cx. pipiens population growth correlates and have lasting effects on traits that relate to a mosquito's ability to vector pathogens.

The effects of resource type and ratio on competition with Aedes albopictus and Culex pipiens (Diptera:Culicidae).

The introduction of Aedes albopictus (Skuse) in the United States has been associated with declines in abundance of resident mosquito species, presumably because of resource competition, as larvae of Ae. albopictus have been illustrated as superior competitors under certain resource conditions. We evaluated the hypothesis that varying the type and ratio of two food resources (Foxtail grass: American elm) alters the competitive outcome of Ae. albopictus and Culex pipiens (L.). We measured survivorship, development time, size, and adult longevity, and estimated the population growth index (A') of populations raised both alone and in equal number with the interspecific competitor, across five ratios of the two food resources. Competition was asymmetric with Ae. albopictus, the superior competitor across all resource treatments; however, the competitive advantage Ae. albopictus had over Cx. pipiens was reduced as grass became the predominant resource. With elm as the predominant resource, the population growth index (A') for both Ae. albopictus and Cx. pipiens was lower in intraspecific and interspecific competition treatments, respectively. The treatments also impacted adult life history, as life spans of both Ae. albopictus and Cx. pipiens varied when they emerged from larval conditions with different resource and competition treatments. We discuss the possible differences in the two species' efficiencies in exploiting the two resource types. Despite some resource conditions alleviating the competitive effects of Ae. albopictus on Cx. pipiens, competition remained asymmetric; thus, additional mechanisms are likely operating under field conditions when the two species coexist.

Homage to Robert Lee Metcalf (1916-1998): entomologist, environmental toxicologist, and insect chemical ecologist.

The late Professor R.L. Metcalf is being honored as one of the leading entomologists of the 20th century, whose worldwide influence on entomology, insecticide and environmental toxicology, and insect chemical ecology was enormous. His 82-year life span mirrored the transition in entomology from the early descriptive phase of insect and plant and animal interactions to the more detailed integration of the biochemical, physiological, behavioral, ecological, and environmental understanding of nature within the context of societal issues and needs. New techniques, some relatively simple but never-the-less ingenious, paved his way to fame. Metcalf was an enormously productive scientist. His 450+ research publications, numerous books and editorships, patents, internationally oriented staff of students, postdocs and associates, and his contributions to teaching and to public service let him stand out as a challenging role model for those young minds starting their careers at the beginning of the 21st century.

Isobutyric acid from the Brindley's glands of Triatoma lecticularia.

The contents of the Brindley's gland of Triatoma lecticularia (Stål) (Heteroptera: Reduviidae: Triatominae) have been identified by gas chromatography-mass spectrometry as isobutyric acid. This compound is found in similar secretions from certain other members of the Triatominae, and is suggested to play a role as a defensive pheromone and for intraspecies communication.

Evaluation of methylated soy oil and water-based formulations of Bacillus thuringiensis var. Israelensis and Golden Bear Oil (GB-1111) against anopheles quadrimaculatus larvae in small rice plots.

The efficacy of formulations containing methylated soybean oil (MSO) alone and with technical-grade Bacillus thuringiensis var. israelensis (Bti) were compared to Golden Bear Oil (GB-1111) and a water-based Bti formulation against 3rd- to 4th-stage Anopheles quadrimaculatus larvae confined to sentinel cages in small rice plots. Three replicates each of MSO with 2% Pyroter added as a surfactant (MSO + PYR), MSO with 2% Pyroter and 4 g of Bti technical powder (MSO + PYR + Bti), GB-1111, a water-based formulation with 4 g of Bti technical powder (Bti + water), and untreated controls were performed. Mosquito larvae were introduced on the 1st day of treatment and at 4 days posttreatment. Mortality was recorded at 24 and 48 h posttreatment for the 1st installation and at 5 days posttreatment for the 2nd installation. The Bti + water formulation provided 71% control and the MSO + PYR + Bti formulation achieved 64% control, whereas MSO + PYR and GB-1111 produced 16 and 18% control, respectively, at 24 h posttreatment. With the exception of MSO + PYR + Bti, which decreased by 2%, the mean percent control increased slightly at 48h posttreatment across remaining treatments, with Bti + water obtaining 72% control. This was significantly higher than GB-1111, which achieved 23% control at 48 h posttreatment. The MSO + PYR and MSO + PYR + Bti formulations yielded 56 and 62% control, respectively, during the same interval and were not significantly different from one another. Formulations containing MSO + PYR exhibited delayed activity similar to GB-1111, with all formulations except MSO + PYR + Bti providing greatest control at 48 h posttreatment. Both MSO formulations (MSO + PYR + Bti and MSO + PYR) were statistically comparable to Bti + water and GB-1111, respectively, at 24 and 48 h posttreatment. None of the formulations exhibited a residual activity adequate enough to control An. quadrimaculatus larvae for up to 5 days.

Aedes albopictus and Ae. triseriatus eggs survive waste tire processing.

Tires that were either crudely chopped or more finely processed into shreds contained viable eggs. Field-collected remnants of 2-3 chopped tires contained viable Aedes albopictus eggs. After shredding tires seeded with mosquito eggs, 34 (4.6%) of an estimated 746 Ae. albopictus eggs and 21 (2.7%) of an estimated 774 Aedes triseriatus eggs survived. Chopped and shredded tire remnants may serve as a means of dispersing mosquitoes.

Oviposition preferences of Culex pipiens and Culex restuans for infusion-baited traps.

The number of egg rafts oviposited by Culex pipiens and Culex restuans in infusion-baited ovitraps varied with the type of infusion substrate, infusion age, method of infusion preparation, and calendar date. In one or more tests, more Culex egg rafts were collected from water infused with Kentucky bluegrass sod, mixed grass clippings, straw, or a commercial rabbit chow than from a water control. Infusions prepared with oak leaves, maple leaves, and sod soil were ineffective as Culex oviposition attractants; however, alfalfa infusions ranged from marginally effective to unattractive. Rabbit chow infusions required one or more reinfusions before becoming active oviposition lures when prepared in unconditioned (unused) ovitraps. Infusions prepared in conditioned ovitraps (those that had previously contained the same type of infusion) had shorter delay periods. Effective oviposition lures for Culex species included continuous infusions, such as sod and sod grass, and those in which the substrate was infused in the water for only a brief period (24-48 h), such as infusions of rabbit chow and mixed grass clippings. The percentage of egg rafts from Cx. restuans was usually greater in sod and grass infusions than in rabbit chow infusions, whereas Cx. pipiens showed a slight preference for rabbit chow infusions over sod and grass infusions. The temporal shift in relative oviposition activity of the 2 Culex species (cross-over) varied from year to year and between sites in one year.

Attraction of Aedes albopictus adults in sod infusion.

Aedes albopictus adults were recovered from sod-baited gravid traps at 7 sites in 5 counties of southern and southwestern Illinois in areas ranging from suburban to rural. The attraction of this species to a lure usually associated with members of the Culex pipiens complex was investigated under laboratory and field conditions. Olfactometer and oviposition preference tests in the laboratory showed that Ae. albopictus is attracted to sod infusion and females readily oviposit on substrates in contact with the infusion. Both males and females responded to the sod infusion in the olfactometer. The attraction of multiple mosquito species to sod-baited gravid traps was demonstrated at a waste tire site in Jasper County, Illinois. Females of Ae. albopictus, Aedes triseriatus, and Culex species were collected from gravid traps placed along the edge of woods at distances ranging from 100 to 200 m from the tire site. Only a small percentage of the Ae. albopictus females appeared to be gravid (less than 5%), unlike the majority of Culex and Ae. tristeriatus females.

Notes on the biology of Orthopodomyia in Illinois.

The principal habitats of immature Orthopodomyia alba and Orthopodomyia signifera are tree holes, though they are occasionally encountered in artificial containers. We collected 929 Or. alba and 17 Or. signifera from 2 plastic trash cans, 2 scrap tires, and a tree hole. All collections were made in an urban residential area in central Illinois.

Indole as an olfactory synergist for volatile kairomones for diabroticite beetles.

Olfactory synergism, where combinations of plant volatile kairomones are quantitatively more attractive to insects than the sum of attraction of the individual components, is an important but little-studied phenomenon in host plant selection and feeding and in pollination ecology. Diabroticite beetles (Coleoptera: Chrysomelidae) are strongly attracted toCucurbita blossoms, and 2- to 3-fold olfactory synergism has been demonstrated in four species by combinations of the key blossom volatiles, 1,2,4-trimethoxybenzene, indole, and (E)-cinnamaldehyde. This TIC mixture represents an optimizedCurcurbita blossom volatile kairomone mixture useful in monitoring Diabroticite populations and in studying their behavior and ecology. Indole, which exhibits a spectrum of attraction to these beetles ranging from moderate forDiabrotica virgifera virgifera andAcalymma vittatum to very weak forD. barberi, is the primary synergistic component. Indole combined with 4-methoxycinnamaldehyde was significantly synergistic toD. v. virgifera at a ratio of 1:300 and produced 4-fold synergism at a ratio of 1:1. Indole combined with 4-methoxyphenethanol was less synergistic toD. barberi with 1.5- to 2-fold synergism at a 1:1 ratio. These consistent variations in diabroticite beetle olfactory responses presumably indicate evolutionary divergences in the numbers of relict indole antennal receptors.

Statistical appraisal of the weight-wing length relationship of mosquitoes.

The relationship between wing length and body weight of mosquitoes was examined by comparing the fit of regressions using logarithmic and cubic transformations. A two-parameter line using a double logarithmic transformation provided the best fit, and we found no evidence to justify the use of wing length cubed as a transformation. Wing length was not directly proportional to body weight, but rather increased at a lesser rate than did body weight. Equations that predict body weight from wing length may not be an appropriate substitute for weighing mosquitoes, when studying the extremes of size in populations.

Evolution of diabroticite rootworm beetle (Chrysomelidae) receptors for Cucurbita blossom volatiles.

The diabroticite rootworm beetles coevolved with plants of the family Cucurbitaceae as demonstrated by their feeding dependence on the tetracyclic triterpenoid cucurbitacins. These beetles also exhibit strong attraction to phenylpropanoid volatile components of Cucurbita blossoms. A mixture of 1,2,4-trimethoxybenzene, indole, and (E)-cinnamaldehyde, all blossom components, is highly attractive to the several species of diabroticite cucumber beetles and corn rootworms and is considered a simplified Cucurbita blossom kairomone odor. The evolutionary divergence in antennal receptor complementarity is best understood by comparing the species-specific responses of several Diabrotica to structural analogues of (E)-cinnamaldehyde, the major attractant for Diabrotica undecimpunctata howardi. Cinnamyl alcohol is a strong attractant for Diabrotica barberi, and 4-methoxycinnamaldehyde is an exceptional attractant for Diabrotica virgifera. The very closely related species D. barberi and Diabrotica cristata are most strongly attracted to 4-methoxyphenethanol, which is unattractive to the other species studied.

Extractable hydrocarbons and kin recognition in honeybee (Apis mellifera L.).

Hydrocarbons of worker honeybees of known pedigree were extracted and analyzed using gas chromatography and mass spectrometry. Variability in hydrocarbon extracts of individual workers is determined at least in part genetically. Correlations in hydrocarbon composition of extracts were highest among more closely related individuals. Individuals maintained in groups exchange hydrocarbons but still maintain enough self-produced compounds to retain genetically determined individual characteristics. These results demonstrate that extractable hydrocarbons of bees provide sufficiently reliable genetic information to function as labels for use during kin recognition.

Olfactory responses ofOrius insidiosus (Hemiptera: Anthocoridae) to volatiles of corn silks.

A synomone present in hexane extracts of corn silks was found to attractOrius insidiosus (Say). The attraction was a diurnal, innate behavior, independant of sex. A portion of the prey-searching behavior ofO. insidiosus apparently relies on olfactory perception when corn is the prey's host.

Semiochemical attractants ofDiabrotica undecimpunctata howardi barber, southern corn rootworm, andDiabrotica virgifera virgifera leconte, the western corn rootworm (Coleoptera: Chrysomelidae).

During the summers of 1984 and 1985, a variety of structurally related benzenoid compounds was evaluated in sweet corn plots as attractants for adult southern corn rootworms (SCR), western com rootworms (WCR), and northern corn rootworms (NCR). Field response to the volatiles was measured by beetle counts on baited cylindrical sticky traps placed inside the corn plots at a height of l m above ground level. SCR adults were attracted late in the season (last week of August through September, 1984 and 1985) to numerous aromatic compounds, including phenylacetaldehyde, benzyl acetone, phenethyl alcohol, phenyl acetate, indole, veratrole, methyl eugenol, methyl isoeugenol, eugenol, and isoeugenol. Although many compounds attracted SCR adults late in the season, only veratrole, phenylacetaldehyde, and chavicol were significantly active in early and middle August 1985. WCR adults were attracted to a different group of compounds, namely estragole,trans-anethole, and indole. Estragole (4-methoxy-1-allylbenzene) was an effective WCR attractant from corn tasseling in early August 1985, until the end of the trapping period in late September and early October 1985. Indole andtrans-anethole (4-methoxy-1-propenylbenzene) were less effective attractants than estragole and were most active at the beginning and/or end of the corn season. Traps baited with 100 mg of estragole caught an average of 20 times more WCR adults than unbaited control traps, and the females outnumbered the males in the baited traps. Estragole dosage tests were conducted in three sweet corn plots on different dates in 1985 and the minimum effective dose ranged between 5 and 30 mg/trap. Field tests with structural analogs revealed the importance of the site of unsaturation in the allylic side chain of estragole and the effect of different ring substituents on WCR response. The phenylpropanoids, eugenol and isoeugenol, significantly attracted NCR adults, even though these beetles were in low abundance in the test corn plots. Field tests indicate there is no cross-species response by WCR and NCR adults to their related phenylpropanoid attractants. However, in late August, SCR adults do respond to some WCR and NCR attractants (indole and several eugenol analogs). Electroantennographic analysis of SCR males revealed they can perceive peripherally a wide range of benzenoid compounds.