Baseline susceptibility to imidacloprid and cross resistance patterns in Colorado potato beetle (Coleoptera: Chrysomelidae) populations

During 1995-1998, we tested 134 geographically discrete populations of Colorado potato beetle, Leptinotarsa decemlineata (Say), from the United States, Canada, Germany, France, and Poland for susceptibility to imidacloprid. Neonates were assayed on potato-based agar diet incorporated with imidacloprid and exposed on filter paper to esfenvalerate, azinphosmethyl, and carbofuran to characterize cross-resistance. In all 4 yr, Long Island populations were the most tolerant to imidacloprid, with LC50s ranging up to 29 times higher than the most susceptible populations. Responses to imidacloprid did not change significantly on farms where populations were assayed over time, except for those from Long Island, which doubled in overall tolerance to imidacloprid since 1995. Much of this tolerance was already present before imidacloprid was used on Long Island. Correlative analysis of the populations tested over the 4 yr indicated positive cross-resistance patterns with esfenvalerate and azinphosmethyl. This response was probably caused by preexisting metabolic and excretion mechanisms selected by previous exposure. There was no significant pattern of cross-resistance with carbofuran or bensultap. Regression slopes were also significantly negatively correlated with LC50 values for imidacloprid, indicating higher heterogeneity, which could lead in further resistance development. We discuss the relative sensitivity of diet-incorporated assays with neonates compared with other bioassay studies. Based on a pooled group of susceptible populations tested in 1995, a baseline LC50 of 0.39 ppm and a discriminating concentration of 8 ppm were suggested to detect early stages of resistance in "suspect" populations. We also suggest application strategies for imidacloprid that reduce selection pressure.     

Genetic improvement of Amblyseius finlandicus (Acari: Phytoseiidae): laboratory selection for resistance to azinphosmethyl and dimethoate

Amblyseius finlandicus (Oudemans) was selected in the laboratory for resistance to azinphosmethyl and dimethoate by subjecting adult females to increasing concentrations of dried residues of dimethoate and azinphosmethyl on detached bean leaves. The first eight selections were done with dimethoate. Slide-dip bioassays indicated selection with dimethoate increased dimethoate resistance 1.8-fold and azinphosmethyl resistance 2.6-fold. These resistances appeared to be quite stable: a 1.2 to 1.3-fold decrease in resistance ratios was observed in a subculture after 10 months without selections. No decrease was observed after 9 months without selections in a pooled colony that consisted of both resistant and susceptible mites. The dimethoate-selected colony was subsequently selected eight times with azinphosmethyl. About 15 % of the mites survived the last selection round with 2,500 ppm, which is 2.5 times the highest recommended field rate in Finnish apple orchards. At the end of the selection program, based on slide-dip bioassays, the total increase in resistance to dimethoate was about two-fold and to azinphosmethyl about 5.4-fold compared to the unselected base colony from which the selected colony was derived. The LC₅₀ value for azinphosmethyl was 14 times higher in the selected colony (451.3 ppm a.i.) compared to the most susceptible colony tested. A similar level of resistance to both pesticides was achieved after six azinphosmethyl selections on a mixed colony that was initiated by pooling mites from five field-collected colonies and the dimethoate-selected lines. Year-to-year variation in azinphosmethyl LC₅₀ values of the unselected base colony was high, with values varying from 83.8 to 348.7 ppm a.i., demonstrating the need to test a reference strain in each bioassay. Results of the azinphosmethyl selections and the subsequent slide-dip bioassays suggest that the resistant strain could tolerate field rates of azinphosmethyl (300–950 ppm a.i.) used in Finnish apple orchards.     

Resistance levels ofTyphlodromus occidentalis (Acari: Phytoseiidae) from Washington apple orchards to ten pesticides

Nine Washington populations ofTyphlodromus (=Metaseiulus) occidentalis Nesbitt collected from commercial apple orchards were surveyed for resistance to ten pesticides. A susceptible population collected from wild blackberry which had no history of pesticide exposure was used in estimating resistance development. All populations from apple orchards were tolerant to high concentrations of azinphosmethyl, diazinon, endosulfan and propargite. Resistance was also apparent to these materials, especially for azinphosmethyl which produced over 100-fold resistance levels for several populations. Moderate to low levels of tolerance and resistance development were seen to field concentrations of cyhexatin, formetanate and carbaryl. Fenvalerate, methomyl and methidathion were all very toxic at field concentrations and little evidence of resistance development was apparent. The use of fenvalerate, methomyl or methidathion at a time whenT. occidentalis is active would likely abrogate favorable biological control of pestiferous orchard mites.Scientific Paper No. 7502     

Correlated insecticide cross-resistance in azinphosmethyl resistant codling moth (Lepidoptera: Tortricidae)

Resistance to several classes of insecticides was correlated with azinphosmethyl resistance in codling moth, Cydia pomonella (L.), in California. In tests of laboratory and field populations, cross-resistance was positively correlated with azinphosmethyl and two organophosphates (diazinon, phosmet), a carbamate (carbaryl), a chlorinated hydrocarbon (DDT), and two pyrethroids (esfenvalerate and fenpropathrin). Additionally, negatively correlated cross-resistance was identified between azinphosmethyl and two other organophosphates, chlorpyrifos and methyl parathion. Patterns of resistance observed in laboratory colonies were confirmed with field bioassays. In bioassays of field populations, azinphosmethyl resistance was observed to increase from 1991 to 1993, although levels of resistance remained < 13-fold. Because orchards with azinphosmethyl resistance have had difficulties with suppression of codling moth, and cross-resistance was found for all tested classes of insecticides, strategies for managing resistance will need to be developed so as to protect current and future control tactics. The two insecticides with negatively correlated cross-resistance are discussed as potential tools for resistance management.     

Resistance and cross-resistance to four insecticides in populations of obliquebanded leafroller (Lepidoptera: Tortricidae)

Populations of obliquebanded leafroller, Choristoneura rosaceana (Harris), were collected from organic and conventionally managed orchards located in the Okanagan and Similkameen Valleys of British Columbia Neonate F1 progeny were assayed for resistance to azinphosmethyl, tebufenozide, methoxyfenozide, and indoxacarb using a leaf disk bioassay. Significant differences in resistance levels among populations were observed for all four insecticides. Insects collected from organic sites were more susceptible to all insecticides than were insects collected from conventional sites. Resistance to the benzoylhydrazine insect growth regulators tebufenozide and methoxyfenozide was highly correlated with resistance to azinphosmethyl across populations, indicating cross-resistance between these compounds. The highest levels of resistance were observed with indoxacarb, but resistance levels to indoxacarb did not correlate with those for azinphosmethyl. Dose-response regression lines for tebufenozide were parallel across populations, suggesting that the resistance mechanism(s) were quantitatively, but not qualitatively, different. Cross-resistance between azinphosmethyl and benzoylhydrazine insecticides indicates that a resistance management strategy for obliquebanded leafroller involving the rotation of these materials is not likely to be successful.     

Influence of mixtures of kaolin particle film and synthetic insecticides on mortality of larval obliquebanded leafrollers (Lepidoptera: Tortricidae) from resistant and susceptible populations

Experiments were conducted to determine potential interactions between kaolin particle film and three insecticides on neonate larvae of the obliquebanded leafroller, Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae). Kaolin did not significantly affect the toxicity of azinphosmethyl or indoxacarb to an insecticide-susceptible population when applied simultaneously with either insecticide in a 7-d leaf disk bioassay. Methoxyfenozide was slightly more toxic to the same leafroller population when coapplied with kaolin. When these bioassays were repeated on a multiresistant laboratory strain of C. rosaceana, mixtures of kaolin with either azinphosmethyl or indoxacarb were significantly more toxic than the insecticides alone, 3.1- and 7.7-fold more toxic for azinphosmethyl:kaolin and indoxacarb:kaolin, respectively. Mixtures of kaolin and methoxyfenozide did not differ in toxicity to the resistant leafroller population from the toxicity of methoxyfenozide alone. Kaolin alone had no effect on leafroller mortality over the 7-d duration of the bioassay. Although the toxicities of mixtures of kaolin with azinphosmethyl or indoxacarb are only moderately higher than those of the insecticides alone, they may be high enough to provide control of leafroller populations that have become difficult to manage due to the development of insecticide resistance.     

Selection for pesticide resistance in Aphytis

Field-collected populations of Aphytis holoxanthus DeBach (Hymenoptera: Aphelinidae), a parasite of Chrysomphalus aonidum (L.) (Homoptera: Diaspididae), were tested for malathion and for azinphosmethyl tolerance, and selected for increased resistance. Initial tolerance for malathion was not significantly different between populations, and could not be significantly increased by 30 selection cycles. Two field populations showed relatively high levels of azinphosmethyl tolerance, which were further increased by selection to 24–48 times that of a susceptible laboratory population.The differences in response to the two organophosphorus insecticides are discussed in relation to differences in their modes of application, detoxification by insects and the genetic bottleneck experienced by an imported species.     

Pyrethroid resistance and mechanisms of resistance in field strains of Helicoverpa armigera (Lepidoptera: Noctuidae)

Pyrethroid resistance was found in 54 field strains of Helicoverpa armigera collected between 1995 and 1999 from 23 districts in seven states of India. LD50 values of the field strains ranged from 0.06 to 72.2 microg/larva with slopes of 0.5-3.1. Resistance was highest in regions where pyrethroid use was frequent (four to eight applications per season). Resistance to deltamethrin was exceptionally high with resistance ratios of 13,570 and 27,160 in two strains collected during February 1998 in central India. Resistance to cypermethrin, fenvalerate and cyhalothrin also was high with resistance ratios of >1,000 in four strains collected from central and southern India. Resistance ratios were below 100 in >50% of the strains tested. Pyrethroid resistance was high in strains collected from the districts in Andhra Pradesh where a majority of the cotton farmer suicide cases in India were reported. Resistance to pyrethroids appeared to have increased over 1995-1998 in most of the areas surveyed. Studies carried out through estimation of detoxification enzyme activity and synergists indicated that enhanced cytochrome p450 and esterase activities were probably important mechanisms for pyrethroid resistance in field strains. Pyrethroid nerve insensitivity also was found to be a major mechanism in some parts of the country where the use of pyrethroids was high. The information presented illustrates the importance of proper insect management programs to avoid the consequences associated with improper insecticide use.     

Influence of three resistance sources in winter wheat derived from TAM 107 on yield response to Russian wheat aphid

A study to determine yield response to the Russian wheat aphid, Diuraphis noxia (Mordvilko), was conducted during the 1997-1998 and 1998-1999 growing seasons at three eastern Colorado locations, Akron, Fort Collins, and Lamar, with three wheat lines containing either Russian wheat aphid-resistant Dn4 gene, Dn6 gene, or resistance derived from PI 222668, and TAM 107 as the susceptible control. Russian wheat aphids per tiller were greater on TAM 107 than the resistant wheat lines at the 10x infestation level at Fort Collins and Akron in 1999. Yield, seed weight, and number of seeds per spike for each wheat line were somewhat affected by Russian wheat aphid per tiller mainly at Fort Collins. The infested resistant wheat lines harbored fewer Russian wheat aphids and yielded more than the infested susceptible wheat lines. Wheat lines containing the Dn4, Dn6, and PI 222668 genes contain different levels of antibiosis or antixenosis and tolerance. Although differences existed among sites and resistance, there is a benefit to planting resistant wheat when there is a potential for Russian wheat aphid infestations.     

Genetic analysis of resistance to azinphosmethyl in the pear psylla Cacopsylla pyri

Laboratory selection with azinphosmethyl had little effect on the chemical resistance in Cacopsylla pyri strains, in comparison to the original wild populations. The resistance ratio relative to a susceptible strain varied from 10- to 40-fold depending on the generation studied. Crosses between two resistant strains and the susceptible strain show resistance to be autosomally inherited and semi-dominant in expression. Backcrosses between F1 and the susceptible strain were unable to distinguish unabigously between monogenic and polygenic inheritance. In the majority of experiments, however, the overall dose-response relationship for backcross progeny was consistent with a single gene hypothesis. Additional bioassays showed azinphosmethyl-resistant strain to cross-resistant monocrotophos and phosmet, but not carbamates, pyrethroids, amitraz or the organophosphates chlorpyrifos and mevinphos.     

Susceptibility of leafrollers (Lepidoptera: Tortricidae) from organic and conventional orchards to azinphosmethyl,spinosad, and Bacillus thuringiensis

Populations of obliquebanded leafroller, Choristoneura rosaceana Harris, and three-lined leafroller, Pandemis limitata Robinson, were obtained from seven sites in the Okanagan and Similkameen Valleys of British Columbia and assayed for their responses to three insecticides using a leaf disk bioassay. Lethal concentration ratios (LCRs) were calculated for all populations compared with a susceptible laboratory colony of C. rosaceana; significant variation was detected in response to all three insecticides. LCRs were 0.86-15.52 for azinphosmethyl, 0.38-2.37 for spinosad (Success), and 0.58-4.89 for Bacillus thuringiensis (Foray). Correlation analysis indicated no cross-resistance among the three insecticides. Leafroller populations obtained from apple orchards managed with organic production practices were more susceptible to azinphosmethyl than leafrollers obtained from conventionally managed sites. Conversely, the highest levels of tolerance to B. thuringiensis were observed in the populations from organic sites, possibly reflecting usage patterns; B. thuringiensis is one of the few insecticides allowed under organic production guidelines. All populations were highly susceptible to spinosad, which may be a useful tool for resistance management programs if used judiciously.     

Survey of susceptibilities to monosultap, triazophos, fipronil, and abamectin in Chilo suppressalis (Lepidoptera: Crambidae)

To provide a foundation for national resistance management of the Asiatic rice borer, Chilo suppressalis (Walker) (Lepidoptera: Crambidae), a study was carried out to determine dose-response and susceptibility changes over a 5-yr period in the insect from representative rice, Oryza sativa L., production regions. In total, 11 populations were collected from 2002 to 2006 in seven rice-growing provinces in China, and they were used to examine their susceptibility levels to monosultap, triazophos, fipronil, and abamectin. Results indicated that most populations had increased tolerance to monosultap. Several field populations, especially those in the southeastern Zhejiang Province, were highly or extremely highly resistant to triazophos (resistance ratio [RR] = 52.57-899.93-fold), and some populations in Anhui, Jiangsu, Shanghai, and the northern rice regions were susceptible or had a low level of resistance to triazophos (RR = 1.00-10.69). Results also showed that most field populations were susceptible to fipronil (RR < 3), but the populations from Ruian and Cangnan, Zhejiang, in 2006 showed moderate levels of resistance to fipronil (RR = 20.99-25.35). All 11 field populations collected in 2002-2006 were susceptible to abamectin (RR < 5). The tolerance levels in the rice stem borer exhibited an increasing trend (or with fluctuation) over a 5-yr period for different insecticides, and they reached a maximal level in 2006 for all four insecticides. Analysis of regional resistance ratios indicated that the history and intensity of insecticide application are the major driving forces for the resistance evolution in C. suppressalis. Strategic development of insecticide resistance management also is proposed.     

Enhanced esterase gene expression and activity in a malathion-resistant strain of the tarnished plant bug, Lygus lineolaris

Extensive use of insecticides on cotton in the mid-South has prompted resistance development in the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois). A field population of tarnished plant bugs in Mississippi with 11-fold higher resistance to malathion was used to examine how gene regulation conferred resistance to this organophosphate insecticide. In laboratory bioassays, synergism by the esterase inhibitors S,S,S,-tributylphosphorotrithioate (DEF) and triphenylphosphate (TPP) effectively abolished resistance and increased malathion toxicity by more than 80%. Esterase activities were compared in vitro between malathion susceptible and resistant (selected) strains. More than 6-, 3- and 10-fold higher activities were obtained with the resistant strain using alpha-naphthyl acetate, beta-naphthyl acetate, and p-nitrophenyl acetate, respectively. Up to 95% and 89% of the esterase activity in the susceptible and resistant strains, respectively, was inhibited by 1 mM DEF. Inhibition of esterase activity up to 75% and 85% in the susceptible and resistant strains, respectively, was obtained with 0.03 mM TPP. Esterase activities in field populations increased by up to 5.4-fold during the fall season. The increase was synchronized with movement of the insect into cotton where exposure to pesticides occurred. Esterase cDNA was cloned and sequenced from both malathion susceptible and resistant strains. The 1818-nucleotide cDNA contained a 1710-bp open reading frame coding a 570 amino acid protein which was similar to many insect esterases conferring organophosphate resistance. No amino acid substitution was observed between susceptible and resistant strains, indicating that esterase gene mutation was not involved in resistance development in the resistant strain in Mississippi. Further examination of esterase gene expression levels using quantitative RT-PCR revealed that the resistant strain had a 5.1-fold higher level of esterase mRNA than the susceptible strain. The results of this study indicated that up-regulation of the esterase gene appeared to be related to the development of resistance in the tarnished plant bug.     

In-season changes in resistance to insecticides in Helicoverpa armigera (Lepidoptera: Noctuidae) in India

Discriminating doses of fenvalerate, cypermethrin, quinalphos, and endosulfan were determined with an insecticide-susceptible Helicoverpa armigera (Hübner) strain. In-season changes in insecticide resistance were monitored with discriminating dose assays at weekly intervals throughout the cropping season for 6 yr from 1993 to 1999 in central India. Resistance to pyrethroids was high throughout all seasons. Resistance to 0.75 microg of quinalphos was consistent, with seasonal averages ranging from 23 to 27% survival over the 6 yr. Resistance to 10.0 microg of endosulfan was moderately high at an average of 40-47% survival during 1993-1994 and in 1997-1998. It was lower in 1996-1997 at 27%, and in 1998-1999 at 33%. The weekly monitoring data for all seasons were pooled and the consolidated 6-yr seasonal average profile indicated that resistance to quinalphos and endosulfan was low during September at 21 and 27% survival, respectively, but increased to 28 and 37% by the end of November. Resistance levels to organophosphates and endosulfan increased during the season, depending on the use of these compounds. At almost all monitoring sites, the within-season changes in quinalphos resistance for all seasons through the study period followed a trend similar to that of endosulfan. The results suggest the possibility of cross-resistance between these compounds. Based on this study and the existing information on cotton pest management, we have developed a "window strategy" for cotton pest management with specific emphasis on the management of insecticides for effective control of H. armigera. This strategy has contributed to improved control at reduced costs in extensive trials.     

Genetic and diurnal variation in the juvenile hormone titer in a wing-polymorphic cricket: implications for the evolution of life histories and dispersal

The wing-polymorphic cricket, Gryllus firmus, contains (1) a flight-capable morph (LW(f)) with long wings and functional flight muscles, (2) a flightless morph with reduced wings and underdeveloped flight muscles (SW), and (3) a flightless morph with histolyzed flight muscles but with fully developed wings (LW(h)). The LW(f) morph differed genetically from the SW morph and phenotypically from the LW(h) morph in the size of flight muscles, ovarian growth during the first week of adulthood, and the hemolymph titer of juvenile hormone (JH). This is the first study to document that phenotypes that differ genetically in morphological aspects of dispersal capability and in ovarian growth also differ genetically in the titer of a hormone that potentially regulates those traits. The JH titer rose 9-100-fold during the photophase in the flight-capable LW(f) morph but did not change significantly during this time in either flightless morph. Prolonged elevation of the in vivo JH titer in flight-capable females, by topical application of a hormone analogue, caused a substantial increase in ovarian growth and histolysis of flight muscles. The short-term, diurnal rise in the JH titer in the dispersing morph may be a mechanism that allows JH to positively regulate nocturnal flight behavior, while not causing maladaptive histolysis of flight muscles and ovarian growth. This is the first demonstration of naturally occurring, genetically based variation for diurnal change in a hormone titer in any organism.     

Changes in timing, duration, and symmetry of molt of Hawaiian forest birds

Food limitation greatly affects bird breeding performance, but the effect of nutritive stress on molt has barely been investigated outside of laboratory settings. Here we show changes in molting patterns for an entire native Hawaiian bird community at 1650-1900 m elevation on the Island of Hawaii between 1989-1999 and 2000-2006, associated with severe food limitation throughout the year beginning in 2000. Young birds and adults of all species took longer to complete their molt, including months never or rarely used during the 1989-1999 decade. These included the cold winter months and even the early months of the following breeding season. In addition, more adults of most species initiated their molt one to two months earlier, during the breeding season. Suspended molt, indicated by birds temporarily not molting primary flight feathers during the months of peak primary molt, increased in prevalence. Food limitation reached the point where individuals of all species had asymmetric molt, with different primary flight feathers molted on each wing. These multiple changes in molt, unprecedented in birds, had survival consequences. Adult birds captured during January to March, 2000-2004, had lower survival in four of five species with little effect of extended molt. Extended molt may be adaptive for a nutrient stressed bird to survive warm temperatures but not cool winter temperatures that may obliterate the energy savings. The changing molt of Hawaiian birds has many implications for conservation and for understanding life history aspects of molt of tropical birds.     

Monitoring and characterization of diamondback moth (Lepidoptera: Plutellidae) resistance to spinosad

Fourteen populations of the diamondback moth, Plutella xylostella (L.), were collected from fields of crucifer vegetables in the United States, Mexico, and Thailand in 1999 and 2000 for susceptibility tests with spinosad. Most populations were susceptible to spinosad and similar to earlier baseline values, but populations from Thailand and Hawaii showed high levels of tolerance. A statewide survey in Hawaii in 2000 and 2001 indicated resistance problems on several islands. One colony collected in October 2000 from Pearl City, HI, was subjected to further selection pressure, using spinosad in the laboratory, and then was used as the resistant strain (Pearl-Sel) for other tests. Spray tests using the recommended field rates of spinosad on potted broccoli plants in the greenhouse confirmed that field control failures due to resistance were possible in the areas of these collections. Analysis of probit lines from F1 reciprocal crosses between the Pearl-Sel and S strain indicated that resistance to spinosad was inherited autosomally and was incompletely recessive. A direct test of monogenic inheritance based on the F1 x Pearl-Sel backcrosses suggested that resistance to spinosad was probably controlled by one locus. The synergists S,S,S-tributyl phosphorotrithioate and piperonyl butoxide did not enhance the toxicity of spinosad to the resistant colony, indicating metabolic mediated detoxification was probably not responsible for the spinosad resistance. Two field colonies in Hawaii that were resistant to spinosad were not cross-resistant to emamectin benzoate or indoxacarb. Resistance developed in Hawaii due to the continuous cultivation of crucifers in which as many as 50 applications of spinosad per year may have been made to a common population of P. xylostella in sequential plantings, although each grower might have used the labeled restrictions for resistance management. Resistance management strategies will need to address such cropping and pest management practices.     

Seasonal development and variation in abundance among four annual flight periods in a butterfly: a 20‐year study of the speckled wood (Pararge aegeria)

Insects typically spend the winter in a species‐specific diapause stage. The speckled wood butterfly, Pararge aegeria, is unique in having two alternative diapause stages, hibernating as larvae or pupae. In southern Sweden this creates a seasonal flight pattern with four annual adult flight periods: the first in May (pupal diapause), the second in June (larval diapause), and the third and fourth directly developing offspring generations in July and August, respectively. We address the raison d'être of the two diapause pathways by (1) outdoor rearing of cohorts, and (2) performing transect censuses throughout the season for 20 years. We contend that an early start of next season provides a benefit accruing to pupal diapause; conversely, a large proportion of the offspring from adults of the fourth flight peak are unable to reach the pupal stage before winter, providing a benefit accruing to larval winter diapause. The results obtained show that the two hibernation pathways are unlikely to be genetically distinct because of a strong overlap between the two offspring generations, and because sibling offspring from the third and fourth flight periods are likely to choose either of the two hibernation pathways, thereby resulting in a genetic mixing of the pathways. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 635–649.     

Metabolic mechanisms only partially explain resistance to pyrethroids in Australian broiler house populations of lesser mealworm (Coleoptera: Tenebrionidae)

The susceptibility of six Australian broiler house populations and an insecticide susceptible population of lesser mealworm, Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae), to cyfluthrin, beta-cyfluthrin, gamma-cyhalothrin, and deltamethrin was investigated. One broiler house population had equivalent susceptibility to the susceptible to beta-cyfluthrin and beta-cyhalothrin, with higher susceptibility to cyfluthrin and deltamethrin. The remaining five populations demonstrated strong resistance to cyfluthrin (19-37-fold), the insecticide used most widely for management of A. diaperinus in Australia. Each cyfluthrin-resistant population demonstrated reduced susceptibility to beta-cyfluthrin (resistance ratios were 8-17-fold), deltamethrin (2.5-8-fold), and gamma-cyhalothrin (6-12-fold) compared with the laboratory population, but cross-resistance patterns varied considerably between populations. Adding piperonyl butoxide (PBO) had no effect on the susceptibility of the susceptible population to any of the insecticides, but it increased the susceptibility of each of the five cyfluthrin-resistant populations: to cyfluthrin (synergism ratio range, 1.9-5.0-fold), beta-cyfluthrin (1.6-4.1-fold), and y-cyhalothrin (1.7-2.0-fold). PBO had a more variable effect on susceptibility to deltamethrin, with three of the cyfluthrin-resistant populations being more susceptible to deltamethrin in the presence of PBO, but susceptibility of the remaining two populations was unaffected by adding PBO (synergism ratio range, 0.9-2.5-fold). Overall, the addition of PBO to the four pyrethroids had variable effects on their susceptibility. This variability indicated the presence of other resistance mechanisms in beetle populations apart from metabolic resistance. In addition, the relative importance of metabolic resistance in each beetle population varied widely between pyrethroids. Thus, it cannot be assumed that PBO will reliably synergize pyrethroids against cyfluthrin-resistant lesser mealworm populations when using it to mitigate insecticide resistance.     

Field and storage testing Bt potatoes for resistance to potato tuberworm (Lepidoptera: Gelichiidae)

Potato tuberworm, Phthorimaea operculella (Zeller), is the most serious insect pest of potatoes worldwide. The introduction of the Bacillus thuringiensis (Bt) toxin gene through genetic engineering offers host plant resistance for the management of potato tuberworm. We report on the field and storage studies to evaluate Bt-cry5 potato lines for resistance to potato tuberworm in Egypt under natural infestations and their agronomic performance in both Egypt and Michigan. From 1997 to 2001, field experiments were conducted at the International Potato Center (CIP) Research Station, Kafr El-Zyat, Egypt, and/or Agricultural Genetic Engineering Institute (AGERI), Giza, Egypt, to evaluate resistance to tuberworm. A total of 27 Bt-transgenic potato lines from six different Bt constructs were evaluated over a 5-yr period. After harvest and evaluation of the agronomic trials, storage evaluation of potato tuberworm damage was done at the CIP Research Station. The 1997 field trial was the first field test of genetically engineered crops in Egypt. Field tests to assess potato tuberworm resistance in Egypt were able to differentiate between the Bt-transgenic lines and the nontransgenic lines/cultivars in 1999, 2000, and 2001. The Bt-cry5-Spunta lines (Spunta-G2, Spunta-G3, and Spunta-6a3) were the most resistant lines in field with 99-100% of tubers free of damage. In the 2001 storage study, these lines were also over 90% free of tuberworm damage after 3 mo. NYL235-4.13, which combines glandular trichomes with the Bt-cry5/gus fusion construct, also had a high percentage of clean tubers in the field studies. In agronomic field trials in Michigan from 1997 to 2001, the Bt-transgenic lines in most instances performed similar to the nontransgenic line in the agronomic trials; however, in Egypt (1998-1999), the yields were less than one-half of those in Michigan. Expression of the Bt-cry5 gene in the potato tuber and foliage will provide the seed producer and grower a tool in which to reduce potato tuberworm damage to the tuber crop in the field and storage.