Energy allocation during the maturation of adults in a long-lived insect: implications for dispersal and reproduction

Flight-reproduction trade-offs are weak in a field cage experiment across multiple Drosophila species

Flight-reproduction trade-offs, such that more mobile individuals sacrifice reproductive output (e.g., fecundity) or incur fitness costs, are well-studied in a handful of wing-dimorphic model systems. However, these trade-offs have not been systematically assessed across reproduction-related traits and taxa in wing monomorphic species despite having broad implications for the ecology and evolution of pterygote insect species. Here we therefore determined the prevalence, magnitude and direction of flight-reproduction trade-offs on several fitness-related traits in a semi-field setting by comparing disperser and resident flies from repeated releases of five wild-caught, laboratory-reared Drosophila species, and explicitly controlling for a suite of potential confounding effects (maternal effects, recent thermal history) and potential morphological covariates (wing-loading, body mass). We found almost no systematic differences in reproductive output (egg production), reproductive fitness (offspring survival), or longevity between flying (disperser) and resident flies in our replicated releases, even if adjusting for potential morphological variation. After correction for false discovery rates, none of the five species showed evidence of a significant fitness trade-off associated with increased flight (sustained, simulated voluntary field dispersal). Our results therefore suggest that flight-reproduction trade-offs are not as common as might have been expected when assessed systematically across species and under the relatively standardized conditions and field setting employed here, at least not in the genus Drosophila. The magnitude and direction of potential dispersal- or flight-induced trade-offs, and the conditions that promote them, clearly require closer scrutiny. We argue that flight or dispersal is either genuinely cheaper than expected, or the costs manifest differently than those assessed here. Lost opportunities (i.e., time spent on mate-finding, mating or foraging) or nutrient-poor conditions could promote fitness costs to dispersal in our study system and that could be explored in future.

Physiological Differences Between Seasonal Dimorphs of Agonoscena pistaciae (Hemiptera: Aphalaridae) Elicit Distinct Host Plant Responses, Informing Novel Pest Management Insights

We examined differences in the physiology and life history between dimorphs of the common pistachio psyllid, Agonoscena pistaciae (Burckhardt and Lauterer) (Hemiptera: Aphalaridae), and how they differ in elicitating host plant production of key metabolites and volatile compounds involved in the recruitment of herbivores and natural enemies. Summer morphs had higher activities of glutathione S-transferase, carboxylesterase, acetylcholinesterase, and cytochrome P450 monooxygenase, superoxide dismutase, catalase, peroxidase, phenoloxidase, and a higher total protein content compared to winter morphs, whereas the latter had higher amounts of lipid, carbohydrate, and glycogen. Winter morphs were heavier, with a higher chitin content and longer preoviposition period, but greater fecundity and longevity than summer morphs. A lower LC50 to thiamethoxam for winter morphs resulted in higher mortality following exposure to the recommended rate of this insecticide in a greenhouse trial. Feeding by winter morphs elicited more strongly the release of volatile compounds known to be attractive to other herbivores, whereas feeding by summer morphs elicited more strongly the release of volatiles implicated in the attraction of natural enemies. Feeding by psyllids increased the concentrations of nitrogenous compounds, carbohydrates, vitamins, and amino acids in plants, the winter morph eliciting larger changes and more improved host plant quality. We conclude that winter morphs are more vulnerable targets for chemical control in early spring, whereas management of summer morphs could rely more on conservation biological control.

Octopamine modulates insect mating and Oviposition

The neuro-mechanisms that regulate insect reproduction are not fully understood. Biogenic amines, including octopamine, are neuromodulators that have been shown to modulate insect reproduction in various ways, e.g., promote or inhibit insect mating or oviposition. In this study, we examined the role of octopamine in regulating the reproduction behaviors of a devastating underground insect pest, the dark black chafer (Holotrichia parallela). We first measured the abundance of octopamine in different neural tissues of the adult chafer pre- and post-mating, demonstrating that octopamine decreased in the abdominal ganglia of females but increased in males post-mating. We then fed the adult H. parallela with a concentration gradient of octopamine to test the effects on insect reproductive behaviors. Compared with its antagonist mianserin, octopamine at the concentration of 2 µg/mL resulted in the highest increase in males' preference for sex pheromone and females' oviposition, whereas the mianserin-treatment increased the survival rate and prolonged the lifespan of H. parallela. In addition, we did not observe significant differences in egg hatchability between octopamine and mianserin-treated H. parallela. Our results demonstrated that octopamine promotes H. parallela mating and oviposition with a clear low dosage effect, illustrated how neural substrates modulate insect behaviors, and provided insights for applying octopamine in pest management.

Size-dependent flight capacity and propensity in a range-expanding invasive insect

For capital-breeding insects, all resources available for adult metabolic needs are accumulated during larval feeding. Therefore, body size at adult eclosion represents the total energetic capacity of the individual. For female capital breeders, body size is strongly correlated with lifetime fecundity, while in males, body size, which correlates with fitness, is less understood. In capital-breeding species with wingless, flightless, or dispersal-limited females, flight potential for male Lepidoptera has important implications for mate-finding and may be correlated with body size. At low population densities, failure to mate has been identified as an important Allee effect and can drive the success or failure of invasive species at range edges and in species of conservation concern. Th capital-breeding European subspecies of Lymantria dispar (L.), was introduced to North America in 1869 and now ranges across much of eastern North America. In L. dispar, females are flightless and mate-finding is entirely performed by males. We quantified male L. dispar flight capacity and propensity relative to morphological and physiological characteristics using fixed-arm flight mills. A range of male body sizes was produced by varying the protein content of standard artificial diets while holding other dietary components constant. Wing length, a proxy for body size, relative thorax mass, and forewing aspect were all important predictors of total flight distance and maximum speed. These results have important implications for mate-finding and invasion dynamics in L. dispar and may apply broadly to other capital-breeding insects.

Sublethal Effects of Diamide Insecticides on Development and Flight Performance of Chloridea virescens (Lepidoptera: Noctuidae): Implications for Bt Soybean Refuge Area Management

High-dose and refuge are the most important strategies for delaying resistance evolution in Bt crops. Insecticide sprays in refuge areas could be necessary and may limit refuge effectiveness. Here, we evaluated the sublethal effects of two diamide insecticides (chlorantraniliprole and flubendiamide) on Chloridea virescens life history traits and flight performance. Sublethal concentrations of chlorantraniliprole and flubendiamide increased larval and pre-pupal development times and decreased larval weight; flubendiamide increased pupal development times. Chlorantraniliprole increased adult male longevity and reduced female fertility, while flubendiamide reduced fecundity. Overall life table parameters were negatively impacted by both treatments. Males exposed to either insecticide showed significant reductions in flight duration and distance for unsustained flights (<30 min). The duration and distance of the first flights were reduced when exposed to chlorantraniliprole. Sustained flights (>30 min) were generally unaffected by insecticide exposure and both sexes flew >6400 m in a single flight. The sublethal effects of flubendiamide and chlorantraniliprole on C. virescens' population dynamics could lead to generation asynchrony and provide insufficient susceptible moths when sprayed on refuge crops. However, the distance and duration of flight may still be sufficient to ensure mixing of potentially resistant and susceptible populations from refuge plots.

Factors That Influence Flight Propensity in Anoplophora glabripennis (Coleoptera: Cerambycidae)

The effects of mating status, sex, beetle age, host quality, temperature, and wind speed on the propensity of Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae) to take flight were evaluated using a free flight test in the laboratory. Time to initiate flight, the angle of flight, and flight capability (when beetles were enticed to take flight) were also evaluated. Host quality, mating status, beetle age, sex, temperature, and the interactions between one or more of these were all found to be significant predictors of flight in A. glabripennis in one or more of the experiments. Female flight propensity peaked at sexual maturity and declined thereafter. Both sexes had a higher propensity to take flight from a stem section of dry host material than from a fresh one. Most (78%) males flew at least once during the four mating status/ages tested from a fresh host stem section, while only 43% of the females flew at least once after chewing an oviposition pit. Flight propensity and distance flown increased with temperature and there was no voluntary flight at 15°C. Flight propensity did not increase with wind speeds 0.0-1.0 m/s, but no ascending flight was observed at 0.5 or 1.0 m/s. Time to flight initiation did not vary with the factors evaluated. Implications these results could have on the success of eradication programs are discussed. Specifically, what factors increase the propensity of mated females to disperse, effectively expanding the infestation zone.

Assessing Flight Potential of the Invasive Asian Longhorned Beetle (Coleoptera: Cerambycidae) With Computerized Flight Mills

The Asian longhorned beetle, Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae: Lamiinae), is an invasive woodborer that poses a serious threat to urban and natural landscapes. In North America, this beetle is a quarantine pest, and populations are subject to eradication efforts that consist of the identification, removal, and destruction of infested host material, and removal or prophylactic treatment of high-risk host plant species. To enhance Asian longhorned beetle eradication protocols in landscapes with extensive host availability, we assessed the dispersal potential of male and female adults of varying age, mating, and nutritional status using computerized flight mills. In total, 162 individuals were tethered to computerized flight mills for a 24-h trial period to collect information on total distance flown, flight times and velocities, and number and duration of flight bouts. Adult Asian longhorned beetles (in all treatments) flew an average of 2,272 m within a 24-h period, but are capable of flying up to 13,667 m (8.5 miles). Nutrition and age had the greatest impacts on flight, with Asian longhorned beetle adults >5 d of age that had fed having greater overall flight performance than any other group. However, mating status, sex, and body size (pre-flight weight and elytron length) had a minimal effect on flight performance. This information will be useful for refining quarantine zones surrounding areas of infestation, and for providing greater specificity as to the risk the Asian longhorned beetle poses within invaded regions.

The Role of Sex and Mating Status in the Expansion Process of Arhopalus rusticus (Coleoptera: Cerambycidae)-an Exotic Cerambycid in Argentina

In Córdoba province, central Argentina, there is an area of introduced pine trees, in which an invading Cerambycid, Arhopalus rusticus (L.), was detected in this region for the first time in 2006. The species has since expanded its range until it now occupies the whole area. Arhopalus rusticus is a common species in pine forests of the northern hemisphere. In this paper, we analyze how sex and mating status affects flight performance and the potential distribution of this species. The study was performed with individuals collected from introduced pine forests in the center-west of Córdoba Province (Argentina). The dispersal capability of A. rusticus was determined by measuring flight speed and distance traveled by recently emerged mated and unmated A. rusticus in flight mills. Data of preflight body weight, postflight body weight, body length, and elytron size were obtained from the individuals that were flown in the flight mill. We found that females had a greater body length, weighed more, had longer elytra, and were stronger flyers than males. We also found that mated individuals flew faster and longer distances than unmated individuals, and consumed a smaller fraction of their body weight. A positive ratio was observed between elytra size and flight speed. A map of males' and females' dispersal distances was produced for the study region, using the adjusted dispersal distance distribution of males and females. The flight performance showed that, as females disperse after copulation, they increase the chances of establishing the species in unoccupied areas.