Growth compensation and faster development of Colorado potato beetle (Coleoptera: Chrysomelidae) feeding on potato foliage expressing oryzacystatin I

Feeding, growth, development, and food conversion efficiency of Colorado potato beetle larvae reared on foliage from a “Kennebec” potato line expressing oryzacystatin I (OCI) at about 1% of its total soluble proteins were compared to those of larvae feeding on untransformed foliage from the same line. During stages L1 to L3, larvae feeding on OCI consumed leaf material 14% faster, gained weight 28% faster, and weighed 20% more at the end of the L3 stage, compared to controls. Continued exceptional performance on OCI during the final L4 stage was expressed as faster development than controls, an effect that persisted during pupal development and resulted in emergence of similar weight adults 1 day earlier than controls. Larvae initially maintained on control foliage and switched to OCI foliage during L4 did not overcompensate as those on OCI foliage throughout development, but performed similarly to larvae on control foliage throughout. Total azocaseinase activity in midgut extracts from these 4th instars 1 d after switching to OCI foliage was sensitive to inhibition by a recombinant form of OCI expressed in Escherichia coli, but was no longer sensitive 4 d after switching, indicating a gradual adaptation of the insect digestive protease system, based on the production of OCI insensitive proteases. Despite OCI potato foliage being consumed faster by small larvae using it for food, there was no indication that it was less efficient than untransformed foliage as food protein. Arch. Insect Biochem. Physiol. 40:69–79, 1999. © 1999 Wiley‐Liss, Inc.     

Molecular interactions between an insect predator and its herbivore prey on transgenic potato expressing a cysteine proteinase inhibitor from rice

Transgenic plants expressing resistance to herbivorous insects may represent a safe and sustainable pest control alternative if they do not interfere with the natural enemies of target pests. Here we examined interactions between oryzacystatin I (OCI), a proteinase inhibitor from rice genetically engineered into potato (Solanum tuberosum cv. Kennebec, line K52) to increase resistance to insect herbivory, and the insect predator Perillus bioculatus. This stinkbug is a relatively specialized predator of caterpillars and leaf-beetle larvae, and may also include plant sap in its predominantly carnivorous diet. One of its preferred prey is Colorado potato beetle (Leptinotarsa decemlineata), a major target of insect resistance development for potato field crops. Gelatin/sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) confirmed that a major fraction of proteinase (gelatinase) activity in P. bioculatus extracts is OCI-sensitive. Among five gelatinolytic bands detected, the slowest-moving one (proteinase I) was inhibited strongly by purified OCI expressed in Escherichia coli or by OCI-transgenic potato extracts, while three other proteinases were partly sensitive to these treatments. There was also evidence of slight inhibition of proteinase I by untransformed potato foliage, suggesting the presence of a natural inhibitor related to OCI at low level in potato foliage. Interestingly, only about 50% of the maximum potential activity of proteinase I was recovered in extracts of P. bioculatus feeding on L. decemlineata larval prey on a diet of OCI-potato foliage, indicating that the predator was sensitive to OCI in the midgut of its prey. However, P. bioculatus on OCI-prey survived, grew and developed normally, indicating ability to compensate prey-mediated exposure to the OCI inhibitor. Confinement of P. bioculatus to potato foliage provided no evidence that potato plant-derived nutrition is a viable alternative to predation, restriction to potato foliage in fact being inferior to free water for short-term survival of nonfeeding first-instar larvae. These results support the view that OCI, an effective inhibitor of a substantial fraction of digestive enzymatic potential in P. bioculatus, should not interfere with its predation potential when expressed in potato plants fed to its prey at a maximum level of approximately 0.8% of total soluble proteins in mature foliage.     

Fitness and feeding are affected in the two-spotted stinkbug,Perillus bioculatus,by the cysteine proteinase inhibitor,oryzacystatin I

Plant resistance to insect pests based on recombinant proteinase inhibitors (Pis) could interfere with natural enemies of target pests, as their own proteolytic systems may also be sensitive to large spectrum PIs. Oryzacystatin I (OCI) is a potential insect pest resistance factor currently engineered into a variety of crop plants, including potato Solanum tuberosum. Potential for OCI interfering with female reproduction in Perillus bioculatus, a stinkbug predator of Colorado potato beetle, Leptinotarsa decemlineata, was studied by chronic feeding for 18 days on prey loaded with 1–16 μg OCI/day. Mortality of treated females was negligible, but fertility was reduced by up to 50%. Additional dose-dependent effects in reproducing females included delayed oviposition, reduced fecundity, lower egg mass size, and reduced egg eclosion incidence. Females fed for 18 days on OCI at ≤4 μg/day returned to normal oviposition when switched to prey without OCI after 18 days of treatment, but negative effects persisted for at least 10 days at higher doses. Affected reproduction in P. bioculatus is consistent with the use of OCI-sensitive digestive proteinases by this stinkbug. However, azocaseinase activity in whole body extracts of OCI-fed females increased about twofold indicating compensation, and OCI-sensitive proteinases were still present in extracts. When timed for delay to trigger attack on Colorado potato beetle larvae under controlled conditions, stinkbugs feeding on OCI appeared consistently hungrier than controls fed at similar rate, suggesting that predation by stinkbugs exposed to OCI-recombinant foliage would be higher than normal. Arch. Insect Biochem. Physiol. 38:74–83, 1998. © 1998 Wiley-Liss, Inc.     

Reproductive status and flight activity of the overwintered Colorado potato beetle

Mating behavior of post-diapause Colorado potato beetles, Leptinotarsa decemlineata (Say), was observed within an overwintering site, a rotated potato field, newly colonized potato plants, and under laboratory conditions. The influence of spring mating on beetle flight in the presence and in the absence of host plants was investigated using a computer-linked flight mill system. Diapause was terminated simultaneously in male and female beetles, and the first matings were observed as early as within the first 24 h after the beetles emerged from the soil (60–90 DD accumulated). The beetles mated within the overwintering site, the potato field, and the fields rotated out of potatoes. Mating status did not affect flight behavior of overwintered beetles; however, unfed beetles displayed higher flight activity than fed beetles. Most flight activity took place soon after flight muscle regeneration, and then declined sharply by the 5th day after flight initiation. Mating in or near overwintering sites soon after diapause termination might be an important factor in providing gene flow between insecticide-resistant and insecticide-susceptible Colorado potato beetle populations, and should be considered in designing resistance management plans.     

Colorado potato beetle (Coleoptera: Chrysomelidae) feeding, development, and survival to adulthood after continuous exposure to Bacillus thuringiensis subsp. tenebrionis-treated potato foliage from the field

Colorado potato beetle, Leptinotarsa decemlineata (Say), feeding, development, and survival to adulthood were examined after continuously exposing large larvae to Bacillus thuringiensis subsp. tenebrionis-treated potato foliage from the field. In laboratory assays, the overall consumption and the length of period to become prepupae were determined for larvae, which began as 3rd and 4th instars, that were offered potato leaf disks with naturally declining levels of B. thuringiensis residue. In small-cage field experiments, survival to adulthood and the period to adult emergence for beetles confined to potato plants treated with B. thuringiensis beginning as 3rd and 4th instars also were examined. Third instars remaining on plants after a B. thuringiensis application were unlikely to feed and 4th instars consumed only approximately 50% as much foliage as those fed untreated foliage. Many late instars subjected to B. thuringiensis-treated foliage failed to survive to adulthood; 58-83% of these beetles died during the larval stage. Reduced feeding and poor survival of late instars suggest that counts of large larvae after application do not provide a complete picture of the efficacy of the B. thuringiensis treatment. Late instar Colorado potato beetles that were exposed continually to naturally declining levels of B. thuringiensis-treated potato foliage took an average of 1.8-4.5 d longer to become prepupae and 4-8 d longer to emerge as adults compared with those provided with untreated foliage. Delayed emergence of adults that fed on B. thuringiensis-treated potatoes as late instars indicated that development was prolonged in these insects because of ingestion of a sublethal dose of B. thuringiensis.     

Host plant choice experiments of Colorado potato beetle (Coleoptera: Chrysomelidae) in Virginia

Field and laboratory-choice experiments were conducted to understand aspects of host plant orientation by the Colorado potato beetle, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), in Virginia. In laboratory bioassays, L. decemlineata oriented to volatiles emitted by potato, Solanum tuberosum L., foliage over both tomato, Lycopersicon esculentum L., and eggplant, Solanum melongena L., foliage, and eggplant over tomato foliage, all of which had been mechanically damaged. Field choice tests revealed more L. decemlineata adults, larvae, and egg masses on eggplant than on tomato. In other experiments, counts of live L. decemlineata on untreated paired plants and counts of dead beetles on imidacloprid-treated plants did not differ between potato and eggplant. L. decemlineata was significantly attracted to eggplant over both tomato and pepper. To determine whether feeding adults affected orientation to host plants, an imidacloprid-treated eggplant or potato plant was paired with an untreated eggplant or potato plant covered in a mesh bag containing two adult male beetles. Significantly more adults were attracted to eggplant with feeding male beetles paired with another eggplant than any other treatment combination. These results indicate that the presence of male L. decemlineata on plants affects host plant orientation and suggests that the male-produced aggregation pheromone may be involved.     

Modifications in dispersal and oviposition of Bt-resistant and Bt-susceptible Colorado potato beetles as a result of exposure to Bacillus thuringiensis subsp. tenebrionis Cry3A toxin

Laboratory strains of Colorado potato beetle, Leptinotarsa decemlineata (Say), physiologically resistant and susceptible to Bacillus thuringiensis (Berliner) subsp. tenebrionis Cry3A toxin were reared to adults on caged potato plants. Influence of three different diets (transgenic potatoes, regular potatoes, and regular potatoes followed by the transgenic potatoes) on beetle mortality, fecundity, and flight behavior were tested under laboratory conditions. A computer-linked flight mill system was used to quantify beetle flight, and dissections were performed to determine the level of flight muscle development. Susceptible beetles continuously fed on transgenic foliage suffered heavy mortality, did not develop flight muscles, and did not produce any eggs. Resistant beetles continuously fed on transgenic foliage were capable of flight and reproduction; however, it took them longer to initiate flight behavior, and their fecundity was lower than fecundity of other treatments. In both strains, detrimental effects became significantly less severe when the beetles were allowed to feed on regular foliage prior to toxin ingestion. In the resistant strain, ingestion of Cry3A toxin significantly increased flight activity, indicating that physiological resistance was probably reinforced by the behavioral escape from toxic environments. No such response was observed for susceptible beetles. When fed on regular foliage, resistant Colorado potato beetles engaged in significantly fewer flights than susceptible beetles. Behavioral differences between resistant and susceptible beetles observed in the present study are likely to affect gene flow between transgenic crops and adjacent refugia, and should be taken in consideration when designing resistance management plans for transgenic potato crops.     

Co‐expression of the proteinase inhibitors oryzacystatin I and oryzacystatin II in transgenic potato alters Colorado potato beetle larval development

Colorado potato beetle (CPB; Leptinotarsa decemlineata Say, Coleoptera: Chrysomelidae) has shown a remarkable adaptability to a variety of control measures. Although oryzacystatin I and II (OCI and OCII) have potential in controlling pests that use cysteine proteinases for food digestion, expression of a single OC gene in potato exhibited a minimal or no effect on CPB fitness traits. The aim of this study was to examine the effect of coexpressed OCI and OCII in potato (Solanum tuberosum L.) cultivars Desiree, Draga?evka and Jelica on CPB larvae. Growth parameters, consumption rates and food utilization, as well as activity of proteases of CPB larvae were assayed. Second and third instar larvae fed on transformed leaves molted earlier and had higher relative growth and consumption rates than larvae fed on nontransformed leaves, while efficiency of food utilization was unaffected. In contrast, fourth instar maximum weight gain and amount of leaves consumed were about 20% lower for the larvae fed on transgenic potato. Analysis of total protease activity of third instar larvae revealed reduction in overall proteolytic activity measured by azocasein hydrolysis, accompanied with inhibition of cysteine proteinase activity 24 h after ingestion of potato leaves expressing OCI and OCII. However, after long‐term feeding on transformed leaves proteolytic activities of larvae became similar to the controls. Although feeding on OCI/OCII leaves did not affect larval survival, coexpression of OC genes reduced the development time and thus significantly decreased plant damage caused by CPB larvae.     

Host acceptance behaviour of Colorado potato beetle larvae influenced by potato glandular trichomes

ABSTRACT. In no-choice tests, larvae of the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), avoided contact with, and were less frequently observed feeding on, excised foliage of the resistant wild potato Solanum berthaultii Hawkes than on leaves of the cultivated potato, S.tuberosum L. For older larvae, reduced feeding was a consequence of less frequent contact with S.berthaultii leaves. However, first instars appeared unable to penetrate the adhesive barrier presented by glandular trichomes of S. berthaultii , and those that remained on the leaflets fed less often than did first instars on S. tuberosum. Removal of the trichome barrier by wiping leaflets with tissue paper did not attenuate the apparent repellent effect of S. berthaulti foliage, but led to increased incidence of feeding by first instars. Inhibition of larval feeding may therefore rely on a mechanical barrier provided by the glandular trichomes of S.berthaultii.     

Survival and fecundity of Bt-susceptible Colorado potato beetle adults after consumption of transgenic potato containing Bacillus thuringiensis subsp. tenebrionis Cry3A toxin

Survival and fecundity of Colorado potato beetle adults, Leptinotarsa decemlineata (Say), that had or had not fed previously on non-transgenic potato before exposure to transgenic potato containing the Bacillus thuringiensis subsp. tenebrionis Cry3A toxin (Bt) was investigated. In the laboratory, < 5% of first-generation adults survived after two weeks when restricted to Bt foliage since eclosion, but over 85% of adults that had fed initially on non-Bt potato survived exposure to Bt potato for two weeks. In field experiments, less than 0.5% of adults that were exclusively provided Bt potato plants survived overwinter, whereas 44% to 57% survived overwinter when fed non-Bt potato plants for two weeks before being provided Bt potato as a final pre-overwintering host. Survival through the winter increased as the duration of initial feeding on non-Bt potato increased and was similar for beetles provided either tubers or Bt potato plants as a final pre-overwintering host. Only overwintered beetles that fed initially on non-Bt potato before encountering either tubers or Bt potato as a final pre-overwintering host laid eggs the following spring. Survival and reproduction of potato beetle adults after colonizing Bt potato fields should not be adversely affected as long as they have had sufficient time to feed initially on non-Bt potato. Implications for how potato production practices in the Mid-Atlantic US may affect the utility of general resistance management plans for Bt potato are discussed.     

Long-term reduction of cold hardiness following ingestion of ice-nucleating bacteria in the Colorado potato beetle,Leptinotarsa decemlineata

We investigated the effect of ingestion of ice-nucleating bacteria on the supercooling capacity and cold hardiness of the Colorado potato beetle (Leptinotarsa decemlineata Say), a freeze-intolerant species that overwinters as adults in shallow, terrestrial burrows. Ingestion of ice-nucleating bacteria (Enterobacter agglomerans, Pseudomonas fluorescens, Pseudomonas putida, Pseudomonas syringae), fed on slices of potato tuber, caused an abrupt decrease in supercooling capacity. No change occurred in the supercooling capacity of beetles fed Escherichia coli, as this species lacks ice-nucleating activity. Ingestion rates showed that tubers treated with different species were equally palatable. During diapause induction beetles evacuated food from their guts, but nevertheless retained sufficient ice-nucleating bacteria to diminish supercooling. Beetles fed P. fluorescens and P. putida exhibited reduced supercooling even after an 8-wk exposure to simulated winter conditions. Furthermore, P. fluorescens was isolated 10-wk post-ingestion from diapausing beetles. Our data suggest that ingested bacteria may be retained by insects during entry into diapause and that the cold hardiness of candidate crop pests, such as L. decemlineata, may be reduced by feeding them ice-nucleating bacteria prior to winter diapause.     

Feeding behaviour and reproductive biology of Colorado potato beetle adults fed transgenic potatoes expressing the Bacillus thuringiensis Cry3B endotoxin

Colorado potato beetle (Leptinotarsa decemlineata Say) adult longevity and fecundity were studied on transgenic potato clones expressing a Cry3B endotoxin of Bacillus thuringiensis (Bt). Adult longevity and fitness were studied for the first 3 weeks after emergence. Beetle reproductive biology on highly resistant clones, intermediary resistant clones and control potato plants was monitored by dissecting females after 7–15 days of feeding and also by analysing haemolymph protein content after 3 days of feeding. Feeding behaviour on transgenic plants expressing high toxin concentrations and on control plants was monitored individually for 36 newly emerged adult beetles feeding on leaf disks during the first two meals. Lethal Time₅₀ for adult beetles feeding on transgenic clones as the sole source of food was not significantly shorter than for beetles on control clones reared in a growth chamber. Differences tended to be larger when the experiment was conducted in a greenhouse with a less optimal temperature range (LT₅₀ = 9.52 and 10.45 days for two transgenic clones and 13.86 for control). In contrast, female egg production on transgenic plants was almost totally inhibited. Dissection studies indicated that adult males living on high-level Bt-expressing transgenic potatoes were still able to mate and produce mobile sperm, but the females were impaired in their reproductive ability since their ovaries were generally not fully developed. An examination of the haemolymph revealed the protein concentration in females living on transgenic plants to be dramatically reduced ( 50%), and electrophoresis showed a reduced content of vitellogenin in these samples.Feeding behaviour of adult Colorado potato beetles was not affected by the different food plants; this indicates that transgenic potato plants were readily accepted as host plants by beetles. The effects of these findings on the use of transgenic plants as a means of L. decemlineata control are discussed.     

Random movement pattern of fed and unfed adult Colorado potato beetles in bare‐ground habitat

• 1 Although the successful management of the Colorado potato beetle Leptinotarsa decemlineata (Say) depends on the prevention of its dispersal, its walking pattern in the landscape remains poorly understood. In the present study, post‐diapause, early summer, late summer and colony adult beetles, both fed and unfed before release, were tracked with a harmonic radar to establish their walking movement pattern in a bare‐ground field.
• 2 The random walk model successfully described the dispersal of all beetle types, whether fed or unfed.
• 3 The diverse life history of this species was manifested by an increased distance travelled and deviations of individual paths from the random model. Starved post‐diapause beetles travelled furthest and individual paths deviating from random were both local and directed, probably aiming to maximize opportunities for host colonization. Starved early summer beetles also travelled further than fed beetles but relied more on random movement to disperse in the habitat. Starving had little impact on the distance travelled or the path deviations of late summer beetles that are searching for overwintering site rather than hosts.
• 4 The increased displacement of starving beetles over fed beetles corresponded with an increased walking step and index of straightness.
• 5 The impact of starvation on travel distance was greater than expected from laboratory tests.
• 6 In conclusion, the results obtained in the present study suggest a random walking pattern to search arable land until host volatile or visual impulses trigger a more directed walk or flight.

     

Oryzacystatin I expressed in transgenic potato induces digestive compensation in an insect natural predator via its herbivorous prey feeding on the plant

We observed recently that the rice cysteine proteinase inhibitor, oryzacystatin I (OCI) expressed in transgenic potato does not affect growth and development of the two-spotted stinkbug predator (Perillus bioculatus) via its herbivorous prey feeding on the plant. Here we monitored the inhibitory activity of recombinant OCI along this potato --> herbivore --> predator continuum, to determine if the absence of effect was associated with a digestive compensatory response of the predator following inhibition of its proteinases by the recombinant cystatin. After confirming that OCI is present in the plant, and ingested in an active form by potato beetle larvae, quantitative and electrophoretic assays allowed us to determine that the recombinant cystatin (representing about 0.8% of total soluble proteins in leaves) was entirely bound to a approximately 30-kDa target proteinase in the prey's midgut, forming a sodium dodecyl sulphate (SDS)-stable complex detected on immunoblots with an anti-OCI polyclonal antibody. Despite the apparent absence of free, residual OCI in the beetle's midgut, digestive protease activity in the predator, known to include OCI-sensitive activity, was altered negatively when the prey was fed the modified plant. This inhibitory process at the third trophic level was accompanied by a compensatory response in the predator, by which serine-type proteinases were synthesized de novo. Overall, our data suggest that the affinity between OCI and the predator's OCI-sensitive proteinases is: (i) as strong as (or stronger than) the affinity between OCI and the potato beetle 30-kDa-sensitive proteinase; and (ii) stronger than the affinity between these enzymes and the plant endogenous homologue of OCI, potato multicystatin, induced in the plant by potato beetle feeding. Our results also show that predatory organisms can adapt their digestive metabolism to the presence of plant antidigestive proteins ingested by their herbivorous preys. In a broader context, this study stresses the need to monitor the inhibitory effects of PI-expressing plants not only on the herbivorous insects targeted, but also on the organisms likely to consume these pests in the environment.     

Influence of fertilization on the Colorado potato beetle, Leptinotarsa decemlineata, in organic potato production

The abundance of the Colorado potato beetle, Leptinotarsa decemlineata (Say), in organically grown potato did not change significantly in response to increasing rates of dehydrated poultry manure. However, peaks of abundance of larvae were shifted forward in time in response to the high rate of organic fertilizer. Tests using excised foliage showed that the shift was not caused by differential larval mortality or longer developmental times. Time allocation to resting, walking, and feeding by adults was similar regardless of fertilizer rate. Adult foliage consumption was unaffected by organic fertilizer rates in no choice tests and significantly affected in few choice tests. A 22% longer larval development time on plants treated with low fertilizer rate than on plants with high rate was the most significant effect. Even though maximum plant height, canopy, biomass, and yield were significantly smaller in the organic than in conventional plots, the suitability of the plants was not affected except for reduced feeding by summer beetles. Summer adults spent less time feeding and consumed two to five times less foliage on organic potato than on inorganically fertilized and conventionally produced plants. The overall influence of fertilizer on Colorado potato beetle populations was limited and therefore can only play a secondary role in management strategies for organic potato. Avoidance of excessive organic fertilizer that promotes short larval development time and extension of the period over which large Colorado potato beetle larvae are present should be recommended.     

Response of potato aphid (Homoptera: Aphididae) to synthetic potato-derived Colorado potato beetle (Coleoptera: Chrysomelidae) attractant and natural potato odor

A recently synthesized kairomone blend, based on the volatiles produced by potato (Solanum spp.) plants, has been demonstrated to be attractive to both adult and larval stages of the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae). It was subsequently formulated in a viscous inert carrier for field applications and showed potential for aggregating beetles in treated areas of the field. We investigated effects of this kairomone formulation on the potato aphid, Macrosiphum euphorbiae (Thomas) (Homoptera: Aphididae). The response of both winged and wingless adults to natural potato foliage and synthetic kairomone was tested in a Y-tube olfactometer. Aphid response to untreated potato foliage, foliage treated with the kairomone blend, and foliage treated with blank inert carrier also was tested in petri dishes. In addition, aphid densities on field plots treated with kairomone and blank inert carrier were compared with the control plots. The untreated potato foliage was found to be attractive to wingless, but not winged, potato aphids. In the olfactometer, the foliage treated with synthetic Colorado potato beetle kairomone was not attractive to either winged or wingless aphids. In petri dishes, aphids avoided leaflets treated with both kairomone formulation and its blank carrier. There was no statistical difference between any treatments compared in the field.     

Monitoring diapause development in the Colorado potato beetle, Leptinotarsa decemlineata, under field conditions using molecular biomarkers

A multiplex PCR protocol was developed using five diapause-regulated genes to monitor diapause development of the Colorado potato beetle under field conditions. A total of 870 beetles from the Red River valley of North Dakota and Minnesota, USA, were screened for three consecutive years. Out of the 32 possible expression profiles, eight could be arranged in chronological order of diapause development. These eight profiles account for over 92% of the beetles surveyed. Intra-population variation in diapause phenotypes was observed in the field. Some beetles were already in the diapause initiation phase in June when the day length was greater than 17 h. Inter-seasonal variation in the timing of diapause development was also noted. The greatest differences were before the day length decreased to less than 15 h. Anomalies in the results, e.g., the presence of the diapause maintenance phase profiles in beetles collected on the potato plants, argue that laboratory results are not always equivalent with what is observed under field conditions.     

Combining genetic engineering and traditional breeding to provide elevated resistance in potatoes to Colorado potato beetle

The sustainable deployment of resistant crop varieties is a critical issue for the implementation of biotechnology in crop pest management. Feeding, biomass accumulation, and mortality were evaluated for susceptible, insecticide‐resistant, and Bacillus thuringiensis (Bt) Cry 3A‐selected Colorado potato beetle (Leptinotarsa decemlineata Say) (Coleoptera, Chrysomelidae) larvae fed on: cultivated potato, a Solanum chacoense line expressing leptine glycoalkaloids, a transformed line expressing Bt toxin, or the leptine line transformed to express Bt toxin. Larvae selected for resistance to Bt‐Cry3A performed better on Bt foliage, but not as well on the leptine foliage, compared to susceptible or insecticide‐resistant larvae. Neither leptine nor Bt toxin completely inhibited the feeding and growth of 3rd and 4th instars of all three strains of Colorado potato beetle. However, for all three strains of Colorado potato beetle on leptine + Bt foliage, feeding was almost zero, growth was zero or negative, and mortality was near 100%.     

Effect of diet and feeding history on flight of Colorado potato beetle, Leptinotarsa decemlineata

We evaluated the hypothesis that Colorado potato beetle (Leptinotarsa decemlineata Say) (CPB) flight frequency is related to diet, and that it changes with duration of food unavailability or exposure to poor quality food by exposing adult overwintered and summer CPB populations to an acceptable host plant (conventional foliage), a poor host (insect resistant transgenic foliage expressing Bacillus thuringiensis tenebrionis[Btt] Cry3a toxin) and no host. Exposure to poor host and no host treatments (with or without water) decreased mean daily flight frequencies and the overall number of overwintered CPB flying, but increased the mean daily flight frequency and number of summer population CPB that flew. Overwintered CPB did not react to an absence of plants at emergence whereas summer CPB increased mean daily flight frequencies when plants and water were not available. The flight response to insect resistant foliage was similar to that for starvation treatments in both populations indicating that flight may not be triggered by Btt toxins but by starvation brought on by feeding on poor quality food. Flight was observed in all treatments for the duration of the test with two exceptions; overwintered beetles fed insect resistant foliage ceased flying after day 17 and summer beetles starved without water ceased after day 8 of a 29‐day study.