Marcos Kogan

Plant volatiles as insect attractants

One of the most interesting aspects of coevolution deals with the interrelationship between the 250,000 odd species of flowering plants and the perhaps 500,000 species of insects that are associated with them in various ecosystems. These coevolutionary relationships began in the early Carboniferous period when land plants first began to diversify and insects began to diversify into modern orders. Chemical ecology lies at the interface between these two enormous groups of very different life forms. There are perhaps 100,000 different secondary plant compounds: terpenoids, alkaloids, phenyl propanoids, esters, acids, alcohols, ketones, and aldehydes produced in the chemical factories of the plant kingdom, and the great preponderance of these act as allomones, kairomones, and synomones in regulating and controlling ecology at the plant‐insect interface. This review will explore current knowledge in this area, with emphasis on the chemical communications involved between these two great groups of life forms. ...

SPECTRAL SPECIFIC RESPONSES IN THE VISUAL BEHAVIOR OF THE GREENHOUSE WHITEFLY, TRIALEURODES VAPORARIORUM (HOMOPTERA: ALEYRODIDAE)

Attraction of the greenhouse whitefly Trialeurodes vaporariorum Westw. to reflected and to transmitted light of various wavelength compositions was measured by trapping and counting adults on greased, colored surfaces. The wavelength composition of the reflecting or transmitting surfaces was spectrophotometrically determined.

Effect of soybean phytoalexins on the herbivorous insects mexican bean beetle and soybean looper

Effects of soybean phytoalexins on the feeding of the soybean looper and Mexican bean beetle were investigated to test the hypothesis that phytoalexins might be a defense mechanism of plants against insects as well as against pathogens. Short-term behavioral responses to the phytoalexins were analyzed using dual-choice tests with phytoalexin-rich and phytoalexin-poor (control) tissues. Phytoalexin production was elicited with ultraviolet radiation. Results from the dual-choice tests indicated that 6th instar soybean looper larvae fed equally on the control and phytoalexin-rich tissues. Feeding by adult and 4th instar Mexican bean beetles, however, was strongly deterred by the phytoalexins as evidenced by “single-bite” mandible scars on the phytoalexin-rich cotyledon discs. Nutritional effects of the isoflavonoid phytoalexin glyceollin on early instar soybean looper larvae were tested by incorporating the phytoalexin into an artificial medium at a level of 1% dry weight (0.15% fresh weight). The larvae were reared for 7 days from emergence on diets of control and glyceollin-containing media. Although survival on the glyceollin diets was initially less than on the control diets, under the experimental conditions glyceollin had no significant effect on the growth, development, or subsequent survival of the larvae. Efficiency of food utilization (ECI) was reduced, indicating that the phytoalexins may be a mild digestibility-reducing factor for the loopers. Implications of the results for host-plant resistance are discussed.

Influence of induced resistance in soybean on the development and nutrition of the soybean looper and the Mexican bean beetle.

Standard gravimetric technique was used to assess the effect of induced resistance in soybean on the consumption and utilization of food by the Mexican bean beetle (MBB), Epilachna varivestis, and the soybean looper (SBL), Pseudoplusia includens. Induced resistance had significant retarding effects on the development and growth of both SBL and MBB. SBL fed leaves of previously injured soybean plants had a 8.5% longer developmental time through the entire larval stage and a 10.4% lower pupal weight than larvae fed leaves from uninjured plants. MBB fed on leaves from previously injured plants through the first three instars had a 9.1 % longer developmental time and a 16.5% lower final weight than those fed on leaves from uninjured plants. Induced resistance showed no significant effect on total food consumed by either SBL or MBB. Nutritional indices including relative consumption rate (RCR), relative growth rate (RGR), efficiency of conversion of ingested food (ECI), approximate digestibility (AD), and efficiency of conversion of digested food (ECD) were calculated on dry weight measurements. In general, induced resistance had greater impacts on the performance of MBB than on that of SBL.

Bioassays for Measuring Quality of Insect Food

Measurement of food quality requires evaluation of the effects of a diet on physiological processes that maximize progeny production and survival, the key parameters of fitness (Williams, 1966). Slansky (1982) suggested that the amount, rate, and quality of food consumed by larvae affected growth rate, developmental time, final body weight, movement, and survival. Amount, rate, and quality of food for adults influence fecundity, longevity, movement, and competitive ability. Larval food quality may additionally affect pupal and adult phenotypic characteristics. Obvious effects of inadequate larval diets are pupal distortions and wing malformations in the imago. For example, such effects characterize the toxicity of L-canavanine to Manduca sexta L., the tobacco hornworm (Rosenthal and Dahlman, 1975).

Attachment of the potato leafhopper to soybean plant surfaces as affected by morphology of the pretarsus

The pulvilli of the potato leafhopper, Empoasca fabae (Harris), seem to provide a suitable mechanism for the attachment of the insect to smooth leaf surfaces. Based on morphological structure of the pretarsal and direct observations, we propose that primary orientation of the leafhoppers on smooth surfaces is achieved through a series of motions involving mainly the pulvilli. The highly irregular surface produced by the trichomes of pubescent soybean cultivars impedes normal attachment for feeding or oviposition. This impediment explains in part the near immunity of pubescent soybean and the converse susceptibility of glabrous soybean plants to the potato leafhopper.

Chemoreceptors of adult Mexican bean beetles: External morphology and role in food preference

The Mexican bean beetle, Epilachna varivestis Mulsant (Coleoptera; Coccinellidae), is an oligophagous insect that accepts leaves of soybean, Glycine max (L.) Merrill, as food but exhibits distinct preferences among varieties. It is believed that the basis for discrimination between the resistant PI 229358 and the susceptible cv. ‘Williams’ is chemical. By the ablation of chemosensilla on antennae, maxillary palpi, labial palpi, and foretarsi, followed with leaf disc preference tests, we found antennal and maxillary palp chemosensilla to be almost entirely responsible for Mexican bean beetles discrimination between foliage of the resistant and susceptible genotypes. All appendages, and the epipharynx, were observed by scanning electron microscopy and, except for foretarsi, were found to bear several types of presumably olfactory and gustatory sensilla, which are figured and described. Since behavioral observations show that olfaction is usually sufficient to cause rejection of PI 229358, we conclude that olfactory sensilla mainly on antennae and maxillary palpi are critical in food discrimination in this system.

Techniques and Applications of Measurements of Consumption and Utilization of Food by Phytophagous Insects

Applications of measurements of consumption and utilization of food by insects are at the interface between alimentary physiology and host selection behavior. It is, therefore, in the basic fields of nutrition, community ecology, and behavior, and in the applied fields of host plant resistance and biological control that one finds studies using consumption indices as analytical criteria.

A contribution to the knowledge of the Brazilian Strepsiptera: (Insecta)

Neste trabalho procuramos atualizar e acrescentar observacoes novas ao conhecimento dos Strepsiptera do Brasil. Descrevemos 4 especies novas da familia Myrmecolacidae, representados apenas por machos e uma especie nova da familia Halictophagidae, representada por macho, femea e hospedador. Registramos a ocorrencia, no Brasil, de uma especie da familia Stylopidae, conhecida anteriormente da Argentina e fornecemos dados adicionais sobre uma especie da familia Mengeidae, Triozocera paulistana Kogan, 1958. Baseados em HOFENEDER & FULMEK (1942-43) damos a lista dos hospedadores encontrados estilopizados no Brasil.

Economic Impact of Public Pest Information: Soybean Insect Forecasts in Illinois

Previous agricultural pest management information studies have focused on the consequences of providing pest information to farmers without access to other sources of pest information. In view of the proliferation of commercial scouting services, this paper uses a preposterior decision model of pest management to examine the outcomes likely to follow from introduction of public pest information into an area with an existing commercial pest information market. Empirical estimates of the impact of a soybean insect forecast system in Illinois demonstrate that although farmers can benefit from public pest information, the implications for pesticide use depend on the reliability of public forecasts.