Grass Hosts of Cereal Aphids (Hemiptera: Aphididae) Between Wheat-Cropping Cycles in South Dakota

Several grasses may serve as alternative hosts for cereal aphids during the interim between small-grain crops in South Dakota, but field studies to determine which grasses are important have not been undertaken. We sampled annual and perennial grasses for cereal aphids in 18 counties in South Dakota in the month of August over three years. Eighty-five of 240 site samples had one or more species of cereal aphids, including 61 of 65 corn sites and 12 of 13 sorghum and sudangrass sites. Four species of cereal aphids were found during the survey: corn leaf aphid, 74 times; bird cherry-oat aphid, 27 times; greenbug, eight times; and English grain aphid, seven times. Abundance of corn leaf aphid on host plants was rated high seven times, moderate 11 times, and low 50 times, and presence only was noted at six other sites. Abundance of bird cherry-oat aphid was rated high four times, moderate four times, and low 19 times. Abundance of English grain aphid and greenbug was always rated low. All high ratings of corn leaf aphid and of bird cherry-oat aphid occurred on field corn. Nine moderate ratings for corn leaf aphid and three for bird cherry-oat aphid occurred on corn. Low frequencies of cereal aphids were found on volunteer small-grains and among weedy grass species such as rough barnyard grass, yellow foxtail, and green foxtail. Cereal aphids were not found on other weedy grasses or on noncultivated grasses. The results suggest that corn and, to less degree, sorghum served as predominant grass hosts of cereal aphids during August in South Dakota. Recent trends of expanding corn acreage in South Dakota may potentially lead to concomitant increases of cereal aphids and intensify the risk of fall infestation of winter grains by cereal aphids

Farmers' Awareness and Use of IPM for Soybean Aphid Control: Survey Results for the 2004, 2005, and 2006 Crop Years

In response to the introduction and rapid spread of soybean aphid as a major new invasive pest of soybean in North America, farmers who attended winter crop meetings in four states in North Central US were surveyed about their treatment of and knowledge about soybean aphids for crop years 2004, 2005, and 2006. Thirteen percent, 84%, and 35% of the farmers indicated they had treated for soybean aphid in 2004, 2005, and 2006, respectively. The average of the soybean acreage treated in each year was 50%, 87%, and 81%, respectively. Overall, the farmers showed a good understanding of soybean aphids and their impact on soybeans. Over 80% knew soybean aphids could repopulate and cause yield damage after an insecticide treatment. Seventy-five percent knew aphids damaged soybeans by sucking sap. Almost 80% said the frequency with which aphids should be treated for profitable control depends on aphid counts, weather conditions, and plant stage. On average, just under 70% considered an average of 250 aphids per plant to be the lowest density for profitable insecticide spraying. Scouting reports were selected by 84 to 94% of the farmers as very important information for the treatment decision; plant growth stage was the second most frequent selection.Crop Production/Industries,

The effect of within-crop habitat manipulations on the conservation biological control of aphids in field-grown lettuce

Within-crop habitat manipulations have the potential to increase the biological control of pests in horticultural field crops. Wildflower strips have been shown to increase the abundance of natural enemies, but there is little evidence to date of an impact on pest populations. The aim of this study was to determine whether withincrop wildflower strips can increase the natural regulation of pests in horticultural field crops. Aphid numbers in plots of lettuce grown adjacent to wildflower strips were compared with those in plots grown in the absence of wildflowers. The presence of wildflower strips led to a decrease in aphid numbers on adjacent lettuce plants during June and July, but had less impact in August and September. The decrease in aphid numbers was greatest close to the wildflower strips and, the decrease in aphid numbers declined with increasing distance from the wildflower strips, with little effect at a distance of ten metres. The main natural enemies found in the crop were those that dispersed aerially, which is consistent with data from previous studies on cereal crops. Analysis and interpretation of natural enemy numbers was difficult due to low recovery of natural enemies, and the numbers appeared to follow changes in aphid abundance rather than being directly linked to the presence of wildflower strips. Cutting the wildflower strips, to remove floral resources, had no impact on the reduction in aphid numbers achieved during June and July, but decreased the effect of the wildflower strips during August and September. The results suggest that wildflower strips can lead to increased natural regulation of pest aphids in outdoor lettuce crops, but more research is required to determine how this is mediated by natural enemies and how the impact of wildflower strips on natural pest regulation changes during the growing season

Fungal Pathogens Infecting Soybean Aphid and Aphids on Other Crops Grown in Soybean Production Areas of Michigan

Seasonal prevalence of fungal pathogens infecting soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), was assessed from 2004 to 2006 in two Michigan soybean production areas. In 2005 and 2006 field-collected soybean aphids were incubated, and fungal infection was detected at both sites early in August 2005 during soybean pod development and high soybean aphid densities. Significantly higher proportions of winged aphid morphs were infected (20 and 90% infection at the two sites) than wingless aphid morphs (1 and 3% infection). All cases of mycosis examined involved one pathogen species, Pandora neoaphidis (Remaudiére & Hennebert) Humber (Entomophthorales: Entomophthoraceae). In 2004 and 2005, we surveyed for pathogens of the soy- bean aphid in soybean as well as pathogens in other aphid species feeding on other crop plants (alfalfa, clover, corn, and wheat) by inspecting for sporulating aphid cadavers every 2 to 3 wk during the soybean growing season. Aphid ca- davers were most abundant in alfalfa, especially in August; were less common in clover, corn, and soybean; and were not found in wheat. Pandora neoaphidis was associated with cadavers of Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae) in alfalfa and clover during the same period when soybean aphid infection was detected. Overall, mortality of soybean aphid and other aphid species due to fungal infection was confirmed in Michigan. The results also implicate infected winged soybean aphid morphs as potential agents for fungal dispersal, and A. pisum in alfalfa and clover as a source of fungal propagules for soybean aphid

Silencing of two insulin receptor genes disrupts nymph-adult transition of alate brown citrus aphid

Insulin receptors play key roles in growth, development, and polymorphism in insects. Here, we report two insulin receptor genes (AcInR1 and AcInR2) from the brown citrus aphid, Aphis (Toxoptera) citricidus. Transcriptional analyses showed that AcInR1 increased during the nymph-adult transition in alate aphids, while AcInR2 had the highest expression level in second instar nymphs. AcInR1 is important in aphid development from fourth instar nymphs to adults as verified by dsRNA feeding mediated RNAi. The silencing of AcInR1 or/and AcInR2 produced a variety of phenotypes including adults with normal wings, malformed wings, under-developed wings, and aphids failing to develop beyond the nymphal stages. Silencing of AcInR1 or AcInR2 alone, and co-silencing of both genes, resulted in 73% or 60%, and 87% of aphids with problems in the transition from nymph to normal adult. The co-silencing of AcInR1 and AcInR2 resulted in 62% dead nymphs, but no mortality occurred by silencing of AcInR1 or AcInR2 alone. Phenotypes of adults in the dsInR1 and dsInR2 were similar. The results demonstrate that AcInR1 and AcInR2 are essential for successful nymph-adult transition in alate aphids and show that RNAi methods may be useful for the management of this pest

The Aphids (Homoptera: Aphididae) Associated With Bell Peppers and Surrounding Vegetation in Southern Illinois

Outbreaks of cucumber mosaic virus (CMV) disease, caused by an aphid- transmitted pathogen, greatly reduced yields of bell pepper in southern Illinois in the mid-1990s. To provide the basis for further studies of the roles of individual apbid species in virus transmission, we surveyed aphid flights in and around pepper fields in 1996 and 1997 by using suction traps, interception nets, landing traps, sweep nets, and hand-picking. We collected 78 species of aphids, 15 of which have been reported to transmit CMV to peppers. The most abundant species taken from suction traps and interception nets in combination were Lipaphis erysimi, Rhopalosiphum padi, Rhopalosiphum maidis, Schizaphis graminum, and Aphis craccivora. All of these species are known to transmit CMV to peppers, but the phenology of R. maidis in Illinois suggests it is not the vector that brings CMV to pepper fields to initiate disease outbreaks. Brachycaudus helichrysi was relatively abundant in 1996 in May and June when a CMV outbreak may have been initiated; it was absent in 1997, and CMV infections were rare that season. Two species, Carolinaia carolinensis and Myzus hemerocallis were recorded for the first time in Illinois

Indian Bt cotton varieties do not affect the performance of cotton aphids.

Cotton varieties expressing Cry proteins derived from the soil bacterium Bacillus thuringiensis (Bt) are grown worldwide for the management of pest Lepidoptera. To prevent non-target pest outbreaks and to retain the biological control function provided by predators and parasitoids, the potential risk that Bt crops may pose to non-target arthropods is addressed prior to their commercialization. Aphids play an important role in agricultural systems since they serve as prey or host to a number of predators and parasitoids and their honeydew is an important energy source for several arthropods. To explore possible indirect effects of Bt crops we here examined the impact of Bt cotton on aphids and their honeydew. In climate chambers we assessed the performance of cotton aphids, Aphis gossypii Glover (Hemiptera: Aphididae) when grown on three Indian Bt (Cry1Ac) cotton varieties (MECH 12, MECH 162, MECH 184) and their non-transformed near isolines. Furthermore, we examined whether aphids pick up the Bt protein and analyzed the sugar composition of aphid honeydew to evaluate its suitability for honeydew-feeders. Plant transformation did not have any influence on aphid performance. However, some variation was observed among the three cotton varieties which might partly be explained by the variation in trichome density. None of the aphid samples contained Bt protein. As a consequence, natural enemies that feed on aphids are not exposed to the Cry protein. A significant difference in the sugar composition of aphid honeydew was detected among cotton varieties as well as between transformed and non-transformed plants. However, it is questionable if this variation is of ecological relevance, especially as honeydew is not the only sugar source parasitoids feed on in cotton fields. Our study allows the conclusion that Bt cotton poses a negligible risk for aphid antagonists and that aphids should remain under natural control in Bt cotton fields

Controlling sap-sucking insect pests with recombinant endophytes expressing plant lectin

We developed a novel pest management strategy, which uses endophytes to express anti-pest plant lectins. Fungal endophyte of Chaetomium globosum YY-11 with anti-fungi activities was isolated from rape seedlings, and bacterial endophytes of SJ-10 (Enterobacter sp.) and WB (Bacillus subtilis) were isolated from rice seedlings. Pinellia ternate agglutinin gene was cloned into SJ-10 and WB for expression by a shuttle vector, and YY-11 was mediated by Agrobacterium tumefaciens. Positive transformants were evaluated using PCR and Western blot assay. Recombinant endophytes colonized most of crops, and resistance of rice seedlings, which were inoculated with the recombinant endophytic bacteria, to white backed planthoppers was dramatically enhanced by decreasing the survival and fecundity of white backed planthoppers. Rape inoculated with recombinant endophytic fungi significantly inhibited the growth and reproduction of aphids. Recombinant endophytes expressing PTA may endow hosts with resistance against sap-sucking pests