Dear Anya,

You may be right. However, is not it easier to examine the genitalia?

Determining sex was much easier than getting the wing lengths, yes! All of my specimen are already sexed, measured, and weighed. I guess the dilemma is along these lines: females are heavier, males are longer - so which is larger? I realize this seems a bit arbitrary, but I was curious if anyone had a preference on the matter as I see both units being used without being linked to one another.

Dear Anya,

The best form is to study the genitalia, this procedure allows easily to distinguish the males of the females.

Also if one has experience and in most of the cases, the males of the females can separate observing the final part of the abdomen.

Best regards.

Lewpidopteran dimorphsim is based on following points, size of sucking canal, antennae, wing spots and color, stripes on thorax and abdomen, abdominal T-A legth, body weight,  genitalia, anal cirrus.

Many creatures grow allometrically, and that relationship can be different for males versus females. So try simple correlation analysis: what features correlate with body size for males and for females? If wing length is highly correlated, then try modeling body size = constant + m*wing length. Test if the slope is different for males versus females. This approach should probably be restricted to quantitative data. Something like "the number of stripes on thorax" could be quantitative if there was some range to the data. The technique might not work if the answer is either 4 stripes or 5 stripes.

Different characters often show different allometries. This is particularly true if you compare sexually selected characters with characters that are not sexually selected. Normally, sexual dimorphism is a result of these different allometries.Thus, it is to be expected to "get different stories" when analysing different characters. Also sex related differences in behaviour might lead to sexual dimorphism only in certain traits (cfr. https://www.researchgate.net/publication/233860421_Sexual_dimorphism_in_wing_cell_patterns_in_Xanthocnemis_zealandica_McLachlan_%28Zygoptera_Coenagrionidae%29

Therefore I suggest to analyse more than one variable, preferably characters which are not too closely correlated and to analyse the relatvie allometries to investigate sexual dimorphism.

Article Sexual dimorphism in wing cell patterns in Xanthocnemis zeal...

I think what Sonke means in the last paragraph is that you need to examine several models. For example:

Body weight = wing size for males versus females.

Body weight = canal size for males and females.

And make several more statistical models like the two above.

However, also check to see if a model like Canal size = Wing size is significant. If the model is significant, then only use one model.

An alternate approach would be to use a multivariate model. Try principle component analysis to identify independent variables. Also try discriminant analysis. This approach builds a model to predict gender, and then tests the model's accuracy. Out of this you can get a Mehalanobis distance with is a measure of how far apart males are from females. This is a useful statistic if you have different populations. So I want to know if the difference between males and females changes with elevation. I collect from two elevations. I can then make separate models for each elevation and compare them by testing if the Mahalanobis distance is different between the two populations using a randomization test.

for the sexual dimorphism in the fresh collected insects may be easier in respect of weight, however, pinned insects are not good for this parameter. if you exclude weight from the list; I would like draw your attention toward dr.Ravi Kant Upadhyay's indication, that: Lepidopteran dimorphsim is based on, size of sucking canal, antennae, wing spots and color, stripes on thorax and abdomen, abdominal T-A legth, body weight, genitalia, anal cirrus.

You can have fresh weight and dry weight. In the latter case I would dry the insects in an oven at something like 35C. Make sure that you weigh them quickly as they will absorb moisture as soon as they are removed from the oven. You might transfer them to a different container to weigh them because weight will change as things cool. Try other parameters: femur length (pro-, meso-, metathoracic), tibia length, head capsule width, and so forth. Most of these traits will be highly correlated with body size and with each other. The more data that you have the better your chances of finding important differences and the more complete your picture. This includes both the number of measurements per insect and the number of insects examined.

alright dr.Timothy A Ebert ,but you see for this type of study one consider  insects over the world museums even some time centuries old insects are taken into account (you know every where circumstances are different) therefore, for the weight parameter, freshly collected insects are good whether dry or wet , however;  practically, for the preserved insects weight determination doesn't seem good.

It seems that we are making two different assumptions. I assumed that this was a laboratory or field study, and Anya had full control over her insects. It seems that you are assuming this is a taxonomic study where museum specimens are important. If this is a taxonomic study I would agree with you that weight is a poor character because one cannot control storage conditions. I also would agree that weight is a difficult variable to measure. Fresh weight depends on when the insect last had access to water. If the insect was killed, it also depends on how the insect was stored prior to weighing. Weight may depend on age, especially if the males do not feed. Drying the insect removes these variables. If drying is done according to an exact protocol you can avoid introducing other errors.

Depends on your objectives/hypotheses. If 'body size' overall is of interest (meaning a surrogate of the amount of energy acumulated) body weight would be pertinent. Females probably invest much more into soma (basically reserves for eggs). The differences in wing size vary from one taxón to another, in some genera and families the males are larger, in others is the opposite; wing size may be well suite for intra-sex comparisons...

cheers

I agree with yopu dr.Timothy A Ebert

and I add to the view of dr.Enrique García-Barros that for the synovigenic females you would get different weight at different time even for the pro-ovigenic female you get different weight after different intervals of emergence

In Lepidoptera body size is not a reliable measure of analysis because the size of adults vary depending on the quality and quantity of food obtained during larval development. I better suggest the analysis of the genitalia which is more reliable to verify the sex of the specimen