Leslie Hammack

Single and Blended Maize Volatiles as Attractants for Diabroticite Corn Rootworm Beetles

Synthetic maize volatiles and analogs dispensed singly and blended were tested for attractiveness to western (WCR, Diabrotica virgifera virgifera) and northern corn rootworm beetles (NCR, D. barberi) in maize fields. Newly identified attractants included syn-benzaldoxime, especially for NCR, and β-caryophyllene for WCR females. (±)-Linalool was more effective than was (−)-linalool. Myrcene, (+)-β-pinene, and (−)-β-pinene were unattractive. Adding methyl salicylate to (±)-linalool, (+)-α-terpineol, or β-ionone appeared to synergistically increase capture of WCR females, but dispensing the terpenes in binary blends did not. Dose–response data for methyl salicylate, (±)-linalool, and a blend of both compounds confirmed the synergy. β-Caryophyllene, but not (−)-α-pinene, added to the latter blend produced a further synergistic increase in WCR female capture that did not vary with sesquiterpene dose from 1.0 to 100 mg. Indole addition to the same blend caused an increase in WCR female captures indicative of synergy, assuming that each did not individually lure different segments of the WCR female population. The green leaf volatiles (Z)-3-hexenyl acetate and (Z)-3-hexen-1-ol were unattractive alone and had no influence on efficacy of traps baited with 3.3 mg each of (±)-linalool, methyl salicylate, and β-caryophyllene. The latter mixture captured about half as many WCR females as did 10 mg of 4-methoxycinnamaldehyde, a potent WCR attractant standard. Substituting β-ionone for (±)-linalool yielded a ternary blend that captured more beetles than did the aldehyde and was unaffected by aldehyde addition. Olive oil, which has been used to sustain attractant volatilization, did not affect captures. The results show that the blending of maize volatiles has the potential to greatly improve efficacy of lures having promising applications in corn rootworm population management.

Sexual Dimorphism of Basitarsi in Pest Species of Diabrotica and Cerotoma (Coleoptera: Chrysomelidae)

Abstract Sexual dimorphism in basitarsal pad morphology is described for prothoracic and mesothoracic legs of Diabrotica virgifera virgifera LeConte, Diabrotica barberi Smith & Lawrence, and Diabrotica undecimpunctata howardi Barber (Coleoptera: Chrysomelidae) and for prothoracic legs of Cerotoma trifurcata (Forster) (Coleoptera: Chrysomelidae). On the indicated legs of these diabroticite beetles, the typical structure of the hairy tarsal pads of chrysomelid beetles is replaced proximally on tarsomere 1 of males by a hairless planar ovoid patch that may facilitate maintenance of the mating posture of males upon the elytra of females. This basitarsal patch proved as reliable as the standard supra-anal plate character for establishing sex of these important crop pests.

Corn volatiles as attractants for northern and western corn rootworm beetles (Coleoptera: Chrysomelidae:Diabrotica spp.).

Synthetic corn volatiles and selected analogs were tested in commercial corn fields for attractiveness to feral northern (NCR,Diabrotica barberi) and western corn rootworm beetles (WCR,D. virgifera virgifera). Two new attractants, geranylacetone and α-terpineol, were identified among corn terpenes and compared at four stages in crop development with the phenylpropanoid standards cinnamyl alcohol and 4-methoxy-cinnamaldehyde, with each component at 30 mg/trap. Dose-response relationships (0.1–100 mg/trap) and efficacy of two-component blends (30 mg/component) were also examined. More beetles were captured on traps baited with (+)- than (−)-α-terpineol, but the difference was statistically significant only for WCR. Captures with geranylacetone or (+)-α-terpineol were directly proportional to the logarithm of the attractant dose. WCR females were attracted to as little as 0.1 mg of either compound. WCR males required ≥ 1.0 mg of (+)-α-terpineol and were not attracted to geranylacetone at any dose. NCR required ≥0.3 mg of either attractant and showed less marked response differences between the sexes than did WCR. Geranylacetone and cinnamyl alcohol were equally effective attractants, whereas (+)-α-terpineol was significantly less attractive to WCR but more attractive to NCR than was 4-methoxycinnamaldehyde. Corn terpenes and phenylpropanoid standards produced similar seasonal response patterns in that captures tended to rise in each case as the season progressed, except during silking when no compound was attractive. Mixing corn terpenes or phenylpropanoid standards synergized responses of WCR females, but (+)-α-terpineol suppressed attraction of NCR females to geranylacetone.

Reproductive Traits of Northern Corn Rootworm (Coleoptera: Chrysomelidae) in Relation to Female and Male Body Size

ABSTRACT Diabrotica spp. are serious pests of maize, Zea mays L., and have evolved resistance to cultural and chemical management practices. Transgenic maize producing a rootworm-toxic protein derived from the bacterium Bacillus thuringiensis Berliner provides a new approach to Diabrotica spp. management. Its use requires a refuge of nontransgenic maize to produce susceptible beetles able to mate with any resistant individuals developing on the transgenic variety to slow the evolution of resistance. Such evolution may simultaneously affect fitness related traits such as longevity, fecundity, and body size. We examined the mating behavior and reproductive biology of Diabrotica barberi Smith & Lawrence in relation to male and female body size. Large and small males were reciprocally paired to large and small females for comparison with average sized beetles. Neither the proportion of pairs that copulated nor the precopulation duration varied significantly with size category; however, the duration of copulation was shortest for large males crossed with small females and longest for the reciprocal cross. Large females lived the longest regardless of mating partner. Although small females mated to small males tended to lay the fewest eggs, size category did not significantly affect egg numbers per week of life during a 12-wk oviposition period. Egg production peaked during the first 4 to 5 wk and then steadily declined. These results suggest that resistance to transgenic maize, if associated with small body size, could provide a reproductive disadvantage for resistant females but not males that could prolong efficacy of the transgenic maize.

Field Capture of Northern and Western Corn Rootworm Beetles Relative to Attractant Structure and Volatility

We used field assays to study attraction of feral northern and western corn rootworm beetles (Diabrotica barberi and D. virgifera virgifera) to a series of mostly nitrogenous and benzenoid synthetic compounds allied with host plant and floral aromas. Vaporization rates were obtained for most field-tested compounds and selected additional lures under both ideal and field-representative, but constant, conditions. Although many test compounds showed at least trace activity for one or both species, methyl benzoate and some of its derivatives, notably methyl anthranilate and methyl 4-methoxybenzoate, merited emphasis as effective new lures for females. Structural alteration of methyl benzoate had consistently negative effects on northern corn rootworm captures despite variable effects on release rate, whereas western corn rootworm was more strongly attracted to methyl anthranilate and methyl 4-methoxybenzoate than to the considerably more volatile parent compound. Phenylacetaldoxime was attractive to females of both species, but no more so than syn-benzaldoxime, included as reference. Release rate was disproportionately low for benzaldoxime, as well as other nitrogenous lures, under field compared with ideal conditions. The attractiveness of salicylaldoxime to northern corn rootworm, despite its low field release rate, and the unattractiveness of methyl salicylate, having a methyl ester in place of the oxime group, similarly highlighted importance of the oxime moiety for reactivity of this species.

Volatile semiochemical impact on trapping and distribution in maize of northern and western corn rootworm beetles (Coleoptera: Chrysomelidae)

Abstract 1 Field studies evaluated plant attractants and analogues as tools to move corn rootworm beetles (Diabrotica spp.) into areas to be treated with toxic baits for population suppression via mass removal/annihilation of reproductive adults.

Multiple Mating, Fecundity, and Longevity in Female Northern Corn Rootworm (Coleoptera: Chrysomelidae) in Relation to Body Size

ABSTRACT Diabroticite corn rootworms are significant maize, Zea mays L., pests that have evolved resistance to cultural and chemical management methods. Transgenic maize synthesizing a rootwormtoxic protein originating from the bacterium Bacillus thuringiensis Berliner is an important new management technology. Its use requires a refuge of nontransgenic maize to delay evolution of resistance by generating susceptible beetles capable of copulating with any resistant individuals surviving on the transgenic crop. The evolution of such resistance may concurrently influence a variety of fitness-related characters. Here, we examined multiple mating by female Diabrotica barberi Smith & Lawrence (Coleoptera: Chrysomelidae) in relation to the following fitness-related traits: female longevity, fecundity, and body size of males and females at the first copulation. For the first copulation, large and small males were reciprocally paired to large and small females for comparison with average-sized beetles. Once-mated females were then maintained under conditions conducive to oviposition and paired with averaged-sized males at weekly intervals until death. Although female age at second copulation varied significantly with size category, female age at first copulation, longevity and fecundity did not. Females that mated multiple times lived longer and laid more eggs than did those that mated once. The results suggest that resistance management models may need to consider those females deriving fitness benefits from a second mating.

Male Reproductive Competition and Components of Female Fitness in Relation to Body Size in Northern Corn Rootworm (Coleoptera: Chrysomelidae)

ABSTRACT In insects, larger males generally have a reproductive advantage over smaller males when competing for mating partners. We examined male reproductive competition together with precopulation and copulation durations, female longevity, and fecundity in the northern corn rootworm in relation to the body size of males and females that were combined for mating. Longevity and fecundity were determined for individually caged, mated females. Of the females in 108 combinations of two males and one female, 35 chose not to mate. Of the females in the 73 combinations that resulted in copulation, 38 were small and 35 were large. The proportions of large and small males that mated did not vary significantly with female size, but large males were more than twice as likely as small males to mate. The precopulation duration did not vary with either male or female size, and no interaction occurred between male and female size for either the precopulation or copulation duration. However, both male and female size affected the duration of copulation, with small males copulating longer than large males and large females copulating longer than small females.Nofemale longevity or egg number differences occurredamongthe body size categories of the mating pairs. The implications of the results for insect resistance management are discussed, considering that the evolution of resistance to certain management strategies, such as resistance to the use of insecticides or of Bt maize, may be accompanied by changes in body size.

Spermatophore Size in Relation to Body Size and Pairing Duration in Northern Corn Rootworm (Coleoptera: Chrysomelidae)

ABSTRACT Female insects may choose to mate with males providing the largest nuptial gift via the spermatophore, which may correlate with fitness related characters such as body size. Here, we examined spermatophore size of northern corn rootworm, Diabrotica barberi Smith & Lawrence (Coleoptera: Chrysomelidae), in relation to body size of males and females and in relation to pairing duration. Virgin males and females of known ages were weighed before and after pairing. Pairs were noted as copulating or not copulating. Copulating males lost significantly more weight than did noncopulating males, whereas copulating females gained significantly more weight than did noncopulating females. For copulating pairs, male and female weight before pairing correlated positively. Spermatophore weight correlated positively with male weight before pairing and was estimated to be 0.37 or 0.38 mg, depending on whether weight change data from males or females were used for estimation. Spermatophore mass accounted for ≈4.4% of male body weight. An effect of pairing duration on spermatophore weight was demonstrable only when weight change data from females were used. Implications of the results for management of rootworm resistance to genetically modified maize are discussed.

Mating Success, Longevity, and Fertility of Diabrotica virgifera virgifera LeConte (Chrysomelidae: Coleoptera) in Relation to Body Size and Cry3Bb1-Resistant and Cry3Bb1-Susceptible Genotypes

Insect resistance to population control methodologies is a widespread problem. The development of effective resistance management programs is often dependent on detailed knowledge regarding the biology of individual species and changes in that biology associated with resistance evolution. This study examined the reproductive behavior and biology of western corn rootworm beetles of known body size from lines resistant and susceptible to the Cry3Bb1 protein toxin expressed in transgenic Bacillus thuringiensis maize. In crosses between, and within, the resistant and susceptible genotypes, no differences occurred in mating frequency, copulation duration, courtship duration, or fertility; however, females mated with resistant males showed reduced longevity. Body size did not vary with genotype. Larger males and females were not more likely to mate than smaller males and females, but larger females laid more eggs. Moderately strong, positive correlation occurred between the body sizes of successfully mated males and females; however, weak correlation also existed for pairs that did not mate. Our study provided only limited evidence for fitness costs associated with the Cry3Bb1-resistant genotype that might reduce the persistence in populations of the resistant genotype but provided additional evidence for size-based, assortative mating, which could favor the persistence of resistant genotypes affecting body size.